RU2799400C2 - Audio signal processing device for stereo signal encoding into bitstream signal and method for bitstream signal decoding into stereo signal implemented by using audio signal processing device - Google Patents

Abstract

FIELD: audio signal processing.

SUBSTANCE: technical result consists in providing the possibility of combining PS-coding using the residual signal and adaptive perceptual stereo L/R-or M/S-coding. The technical result is achieved by generating the first signal and the second signal by perceptual decoding of the bitstream signal; generating, in a frequency-dependent or frequency-independent manner, a downmix signal and a residual signal based on: the sum of the first signal and the second signal and the difference of the first signal and the second signal, or the first signal and the second signal; generating an average stereo signal by performing an upmix operation in response to the downmix signal, the residual signal, and parametric stereo coding parameters, wherein the residual signal indicates an error associated with displaying the first signal and the second signal by the downmix signal and parametric stereo coding parameters; and generating a stereo signal by performing an SBR stereo decoding operation in response to the average stereo signal and the SBR stereo parameters.

EFFECT: possibility of combining PS-coding using the residual signal and adaptive perceptual stereo L/R-or M/S-coding.

10 cl, 26 dwg

Description

Scope of technical application

The application relates to the coding of audio signals, in particular to the coding of stereo audio signals, combining parametric coding and waveform coding technologies.

Background of the invention

Joint coding of the left (L) and right (R) channels of a stereo signal allows for more efficient coding compared to independent coding of L and R. The traditional approach to joint stereo coding is mid/side (M/S) coding. In this case, the average (M) signal is formed by adding the L and R signals, for example, the M signal can be of the form

.

.

Similarly, the side (S) signal is formed by subtracting the L and R channels, for example, the S signal has the form

.

.

In the case of M/S coding, instead of the L and R signals, the M and S signals are encoded.

In the MPEG (Moving Picture Experts Group) AAC (Advanced Audio Coding) standard (see ISO/IEC standard document 13818-7), stereo L/R coding and stereo M/S coding can be selected as time dependent and frequency dependent. way. Thus, a stereo encoder may apply L/R encoding to some frequency bands of the stereo signal, while M/S encoding is used to encode other frequency bands of the stereo signal (frequency dependent method). In addition, the encoder may switch between L/R encoding and M/S encoding over time (time dependent method). In MPEG AAC, stereo coding is done in the frequency domain, more specifically in the MDCT (Modified Discrete Cosine Transform) domain. This allows adaptive selection between L/R coding and M/S coding in a frequency-dependent manner as well as in a time-dependent manner. The decision to choose between L/R stereo coding and M/S stereo coding can be based on side signal estimation: when the side signal energy is small, M/S stereo coding, which is more efficient, should be used. Alternatively, deciding between two coding schemes, both of these schemes may be tested, and the selection may be based on the resulting quantization attempts, i.e. on the observed perceptual entropy.

An alternative approach to joint stereo coding is parametric stereo (PS) coding. In this case, the stereo signal is transmitted as a mono downmix signal after encoding the downmix signal with a conventional audio encoder such as an AAC encoder. The downmix signal is a superposition of the L and R channels. The mono downmix signal is transmitted in combination with additional time- and frequency-dependent PS encoding parameters such as inter-channel intensity difference (IID) and inter-channel cross-correlation (ICC). In the decoder, based on the decoded downmix signal and parametric stereo encoding parameters, a stereo signal is reconstructed that is an approximation of the perceived spatial image of the original stereo signal. For reconstruction, the decorrelator generates a decorrelated version of the downmix signal. Said decorrelator may be implemented by means of an appropriate phase filter. PS encoding and decoding is described in "Low Complexity Parametric Stereo Coding in MPEG-4", H. Purnhagen, Proc. Of the 7th Int. Conference on Digital Audio Effects (DAFx'04), Naples, Italy, October 5-8, 2004, pages 163-168. The disclosure from this document is incorporated herein by reference.

The MPEG Surround standard (see document ISO/IEC 23003-1) uses the concept of PS encoding. In an MPEG Surround decoder, a plurality of output channels is created based on a smaller number of input channels and control parameters. MPEG Surround decoders and encoders are built by cascading parametric stereo modules, which in the MPEG Surround standard are called OTT (One-to-Two) modules for the encoder, and R-OTT (Reverse One-to-Two) modules for encoder. The OTT module defines two output channels through a single input channel (downmix) followed by PS encoding parameters. The OTT module corresponds to the PS decoder, and the R-OTT module corresponds to the PS encoder. Parametric stereo coding can be implemented using MPEG Surround with one OTT module on the decoder side and one R-OTT module on the encoder side; this is also called "MPEG Surround 2-1-2" mode. The bitstream syntax may differ, but the underlying theory and signal processing are the same. Therefore, in the following description, all references to PS coding also include parametric stereo coding based on "MPEG Surround 2-1-2" or MPEG Surround.

In a PS encoder (eg, an MPEG Surround PS encoder), a residual signal (RES) may be defined that is transmitted in addition to the downmix signal. This residual signal indicates the error associated with displaying the original channels through their downmix and PS encoding parameters. At the decoder, the residual signal may be used instead of a decorrelated version of the downmix signal. This makes it possible to better reconstruct the waveforms of the original L and R channels. The use of an additional residual signal is described, for example, in the MPEG Surround standard (see document ISO/EEC 23003-1) and in the article "MPEG Surround - The ISO/MPEG Standard for Efficient and Compatible Multi-Channel Audio Coding”, J. Herre et al., Audio Engineering Convention Paper 7084, 122 ^nd Convention, May 5-8, 2007. Disclosures from both documents, in particular their remarks relating to residual signal, are referenced included in this description.

PS residual coding is a more general stereo joint coding approach than M/S coding: M/S coding performs signal rotation when converting L/R signals to M/S signals. Residual PS encoding also performs signal rotation when converting L/R signals to downmix and residual signals. However, in the latter case, the signal rotation is variable and depends on the PS encoding parameters.

Because of the greater generality of the residual PS coding approach, residual PS coding allows certain types of signals, such as a panned mono signal, to be encoded more efficiently than M/S coding. Thus, the proposed encoder makes it possible to efficiently combine parametric stereo coding technologies with stereo coding technologies based on waveform coding.

Often, perceptual stereo encoders, such as the MPEG AAC perceptual stereo encoder, can decide between stereo L/R encoding and stereo M/S encoding, where in the latter case the middle/side signal is generated based on the stereo signal. This choice may be frequency dependent, i.e. some frequency bands may use stereo L/R encoding, while other frequency bands may use stereo M/S encoding.

In a situation where the L and R channels are essentially independent signals, the specified perceptual stereo encoder will generally not use stereo M/S coding, since in this situation this coding scheme does not provide any improvement in coding compared to stereo L /R-encoding. The encoder will go back to the level of simple stereo L/R encoding essentially processing L and R independently.

In the same situation, a PS encoder system will produce a downmix signal that contains both the L and R channels, which prevents the L and R channels from being processed independently. For residual PS encoding, this may mean less efficient encoding compared to stereo encoding, where the stereo L/R coding or stereo M/S coding is adaptively selected.

Thus, there are situations in which the PS encoder outperforms the perceptual stereo encoder with adaptive selection between stereo L/R coding and stereo M/S coding, while in other situations the latter encoder outperforms the PS encoder.

Brief description of the invention

The present application describes an audio encoder system and coding method that is based on the idea of combining PS coding using a residual signal and adaptive perceptual stereo L/R or M/S coding (e.g. AAC perceptual stereo coding in the MDCT domain). This allows you to combine the benefits of adaptive stereo L/R or M/S coding (eg used in MPEG AAC) with the benefits of PS coding with residual signal (eg used in MPEG Surround). In addition, the application describes a corresponding audio signal decoder system and a decoding method.

The first aspect of the application relates to an encoder system for encoding a stereo signal into a bitstream signal. According to one embodiment of the encoder system, the encoder system includes a downmix step for generating a downmix signal and a residual signal based on the stereo signal. The residual signal may cover all or only part of the usable frequency range of the audio signal. In addition, the encoder system includes a parameter determination step for determining PS encoding parameters such as inter-channel intensity difference and inter-channel cross-correlation. Preferably, the PS encoding parameters are frequency dependent. These steps of downmixing and parameter determination are typically part of a PS encoder.

In addition, the encoder system includes means for perceptual coding in the downstream direction relative to the downmix stage, where a choice is made between two coding schemes:

- coding based on the sum of the downmix signal and the residual signal and on the basis of the difference between the downmix signal and the residual signal; or

- coding based on the downmix signal and based on the residual signal.

It should be noted that in the case of encoding based on the downmix signal and the residual signal, the downmix signal and the residual signal may be encoded, or signals proportional to these signals may be encoded. In the case of sum and difference based coding, the sum and difference may be encoded, or may be encoded signals proportional to these signals.

The choice may be frequency dependent (or time dependent), i.e. for the first frequency band, coding based on the sum signal and the difference signal may be selected, while for the second frequency band, coding based on the downmix signal and the residual signal may be selected.

Such an encoder system has the advantage of being able to switch between stereo L/R encoding and PS encoding with residual signal (preferably in a frequency dependent manner): if the perceptual encoding means make a choice (for a specific band or for the entire frequency range) in favor of coding, based on downmix and residual signals, the coding system behaves like a system using standard PS coding with residual signal. However, if the perceptual encoding means make a choice (for a specific band or for the entire frequency range) in favor of coding, based on the sum signal of the downmix signal and the residual signal and the difference signal of the downmix signal and the residual signal, under certain conditions, the summation and subtraction operations are largely compensate for the previous downmix operation (except in the case of a possibly different gain) and thus the overall system can actually L/R encode the entire stereo signal or one of its frequency bands. For example, such conditions occur when the L and R channels of a stereo signal are independent and have the same level, which will be explained in more detail later.

Preferably, the adaptation of the coding scheme is time and frequency dependent. Thus, preferably, some frequency bands of the stereo signal are encoded with an L/R coding scheme, while other frequency bands of the stereo signal are encoded with a PS coding scheme with a residual signal.

It should be noted that in the case of encoding based on the downmix signal and the residual signal, as discussed above, the actual signal that is input to the core encoder can be generated by two successive operations on the downmix signal and the residual signal, which are inverse (except in the case , possibly a different gain). For example, the downmix signal and the residual signal are supplied to the M/S to L/R conversion stage, and then the output signal of the conversion stage is supplied to the L/R to M/S conversion stage. The resulting signal (which is then used for encoding) corresponds to the downmix signal and the residual signal (except in the case of a possibly different gain).

The following embodiment of the invention uses this idea. According to one embodiment of the encoder system, the encoder system, as discussed above, includes a downmix step and a parameter determination step. In addition, the encoder system includes a transformation step (eg, forming part of the encoding means described above). The conversion step generates a pseudo-L/R stereo signal by performing a conversion on the downmix signal and the residual signal. The conversion step preferably performs sum-and-difference conversions where the downmix and residual signal are summed to generate one channel of the pseudo-stereo signal (the sum is possibly multiplied by some factor), and subtract one from the other, generating a second channel of the pseudo-stereo signal ( the difference is possibly multiplied by some factor). Preferably, the first channel (eg, pseudo-left channel) of the pseudo stereo signal is proportional to the sum of the downmix and residual signals, where the second channel (eg, pseudo-right channel) of the pseudo stereo signal is proportional to the difference between the downmix and residual signals. Thus, the downmix signal DMX and the residual signal RES from the PS encoder can be converted to a pseudo-stereo signal L _p , R _p according to the following equations:

_Lp =g(DMX+RES)

_Rp = g(DMX-RES).

.In the above equations, the normalization gain g, for example, has the value

.

The pseudo stereo signal is preferably processed by a perceptual stereo encoder (eg, part of the encoding means). For encoding, select L/R stereo encoding or M/S stereo encoding. The adaptive perceptual stereo L/R or M/S encoder may be an AAC-based encoder. Preferably, the choice between stereo L/R encoding and stereo M/S encoding is frequency dependent; thus, the choice may vary for different frequency bands, as discussed above. In addition, the choice between L/R encoding and M/S encoding is preferably time dependent. The choice between L/R encoding and M/S encoding is preferably made by the perceptual stereo encoder.

The specified perceptual stereo encoder for M/S encoding has the ability to internally calculate (pseudo-) M and S signals (in the time domain or in selected frequency bands) based on the pseudo-stereo L/R signal. The indicated M and S signals correspond to the downmix and the residual signals (except in the case of a possibly different gain). Thus, if a perceptual stereo encoder opts for M/S encoding, then it actually encodes the downmix and residual signals (which correspond to pseudo M and S signals) as might be done in a system using standard PS encoding with residual signal.

In addition, under specific conditions, the transform step largely compensates for the previous downmix operation (except in the case of a possibly different gain), and thus the encoder system as a whole can actually L/R encode the entire stereo signal, or one from its frequency bands (if L/R encoding is selected by the perceptual encoder). This case corresponds, for example, to the case where the L and R channels of a stereo signal are independent and have the same level, which will be explained in more detail later. Thus, for a given frequency band, a pseudo-stereo signal matches or is substantially proportional to a stereo signal if - for that frequency band - the left and right channels of the stereo signal are substantially independent and have substantially the same level.

Thus, the encoder system actually allows switching between stereo L/R encoding and PS encoding with residual signal in order to be able to adapt to the properties of a given stereo input signal. Preferably, the adaptation of the coding scheme is time and frequency dependent. Thus, preferably, some frequency bands of the stereo signal are encoded with an L/R coding scheme, while other frequency bands of the stereo signal are encoded with a PS coding scheme with a residual signal. It should be noted that M/S encoding is essentially a special case of PS encoding with residual signal (because L/R to M/S conversion is a special case of PS encoding downmix operation), and thus the system encoder can also perform full M/S encoding.

This embodiment, comprising the step of converting downstream to the PS encoder and upstream to the perceptual stereo L/R or M/S encoder, has the advantage that a conventional PS encoder and traditional perceptual encoder. However, the PS encoder, or perceptual encoder, in this case can be adapted for a specific use.

The new concept improves the efficiency of stereo coding by allowing PS coding and joint stereo coding to be efficiently combined.

In accordance with an alternative embodiment of the invention, the coding means discussed above includes a transform step for performing a sum and difference transform based on the downmix signal and the residual signal for one or more frequency bands (for example, for the entire usable frequency band or only for one frequency band). This transformation may be performed in the frequency domain or in the time domain. The conversion step generates a pseudo-left/right stereo signal for one or more frequency bands. One channel of the pseudo-stereo signal corresponds to the sum, and the second channel of the pseudo-stereo signal corresponds to the difference.

Thus, in the case where the encoding is based on the sum and difference signals, the output signal of the transformation step can be used for encoding, while in the case where the encoding is based on the downmix and the residual signal, upstream signals relative to coding stage. Thus, this embodiment does not use two successive sum and difference conversions on the downmix and residual, resulting in the downmix and residual (except in the case of a possibly different gain).

When selecting encoding based on the downmix signal and the residual signal, the parametric stereo encoding of the stereo signal is selected. When sum-and-difference coding is selected (ie pseudo-stereo coding), L/R coding of the stereo signal is selected.

The transform step may be an L/R to M/S transform step that is part of a perceptual encoder with an adaptive choice between stereo L/R and M/S encoding (possibly unlike the traditional L/R to M/S transform step). , the gains are different). It should be noted that the decision to choose between stereo L/R and M/S encoding should be reversible. Thus, an encoding based on the downmix signal and a residual signal is selected (i.e., the encoded signal does not pass the transform stage) when the decision means decides on perceptual M/S decoding, and the encoding based on pseudo-stereo of the signal generated by the transform step is selected (ie, the encoded one passes the transform step) when the decision means make a decision about perceptual L/R decoding.

An encoder system according to any of the embodiments of the invention discussed above may include an additional SBR (spectral band replication) encoder. SBR is a form of HFR (High Frequency Reconstruction). The SBR encoder determines additional information for reconstructing the higher frequency range of the audio signal in the decoder. The perceptual encoder encodes only the lower frequency range, which reduces the bit rate. Preferably, the SBR encoder is connected upstream of the PS encoder. Thus, the SBR encoder may be in the stereo region and generate SBR parameters for the stereo signal. This will be discussed in more detail in connection with the graphics.

Preferably, the PS encoder (ie, the downmix step and the parameter determination step) operates in the resampled frequency domain (the PS encoder, which is discussed below, also preferably operates in the resampled frequency domain). For upstream time-to-frequency conversion with respect to the PS encoder, a hybrid complex-valued filter bank containing a QMF (quadrature mirror filter) and a Nyquist filter can be used as described in the MPEG Surround standard (see ISO/IEC 23003-1 document). This allows adaptive signal processing in time and frequency in the absence of audible aliasing artifacts. Adaptive L/R or M/S coding, on the other hand, is preferably performed in the region of the critically sampled MDCT (eg, as described in AAC) in order to provide an efficient representation of the quantized signal.

The conversion between the downmix and residual signals and the pseudo L/R stereo signal can be done in the time domain, since the PS encoder and the perceptual stereo encoder are usually coupled in the time domain anyway. Thus, the conversion step for generating the pseudo-L/R signal can perform operations in the time domain.

In other embodiments of the invention, which are discussed in connection with the drawings, the transform step performs operations in the oversampled frequency domain or critically sampled MDCT domain.

The second aspect of the application relates to a decoder system for decoding a bitstream signal generated by the encoder system discussed above.

According to one embodiment of a decoder system, the decoder system includes perceptual decoding means for decoding based on a bitstream signal. The decoding means is configured to generate by decoding the (internal) first signal and the (internal) second signal, and to output the downmix signal and the residual signal. The downmix signal and the residual signal are selectively based on

- the sum of the first signal and the second signal and on the difference between the first signal and the second signal

or

- on the first signal and on the second signal.

As discussed above in connection with the encoder system, in this case, the choice can also be frequency dependent and frequency independent.

In addition, the system includes an upmix step for generating a stereo signal based on the downmix signal and the residual signal, where the upmix operation of the upmix step depends on one or more parametric stereo coding parameters.

Similar to the encoder system, the decoder system actually allows switching between L/R decoding and PS decoding with residual signal, preferably in a time and frequency dependent manner.

According to another embodiment of the invention, the decoder system includes a perceptual stereo decoder (eg, part of the decoding means) for decoding the bitstream signal, where the decoder generates a pseudo stereo signal. The perceptual decoder may be an AAC-based decoder. For a perceptual stereo decoder, perceptual L/R decoding or perceptual M/S decoding is selected in a frequency-dependent or frequency-independent manner (the actual selection is preferably controlled by the encoder's decision, which is transmitted as side information in the bitstream). The decoder makes a choice of decoding scheme based on the encoding scheme used for encoding. The coding scheme to be used may be indicated to the decoder by information contained in the received bitstream.

In addition, a conversion step is provided for generating a downmix signal and a residual signal by performing a pseudo-stereo signal conversion. In other words, the pseudo-stereo signal received from the perceptual decoder is converted back into downmix and residual signals. This conversion is a sum and difference conversion: the resulting downmix is proportional to the sum of the left channel and right channel of the pseudo stereo signal, the resulting residual signal is proportional to the difference of the left channel and right channel of the pseudo stereo signal. Thus, a quasi-conversion of L/R to M/S is carried out. A pseudo-stereo signal with two channels L _p , R _p can be converted into downmix and residual signals according to the following equations:

.

.

. Остаточный сигнал RES, используемый в декодере, может покрывать весь используемый диапазон частот звукового сигнала или только часть используемого диапазона частот звукового сигнала.In the above equations, the normalization gain g may, for example, be

. The residual signal RES used in the decoder may cover the entire usable frequency range of the audio signal, or only a portion of the usable frequency range of the audio signal.

The downmix and residual signals are then processed in the upmix step of the PS decoder to produce the final stereo output signal. The upmixing of the downmix and residual signals to a stereo signal depends on the received PS encoding parameters.

According to an alternative embodiment of the invention, the perceptual decoding means may include a sum-and-difference transform step for performing a transform based on the first signal and the second signal for one or more frequency bands (eg, for the entire usable frequency band). Thus, the conversion step generates a downmix signal and a residual signal in the case where the downmix signal and the residual signal are based on the sum of the first signal and the second signal and on the difference of the first signal and the second signal. The transform step may perform operations in the time domain or in the frequency domain.

As similarly discussed in connection with the encoder system, the transform step may be an M/S to L/R transform step forming part of a perceptual decoder with an adaptive choice between stereo L/R and M/S decoding (perhaps the gain different from the traditional M/S to L/R conversion step is different). It should be noted that the choice between stereo L/R and M/S decoding should be reversible.

The decoder system according to any of the previous embodiments of the invention may include an additional SBR decoder for decoding additional information from the SBR encoder and for generating a high frequency component of the audio signal. Preferably, the SBR decoder is located downstream of the PS decoder. This will be discussed in more detail in connection with the graphics.

Preferably, the upmixing step performs operations in the oversampled frequency domain, for example, in the upstream direction relative to the PS decoder, a hybrid filterbank can be used as described above.

The L/R to M/S conversion can be performed in the time domain, since the perceptual decoder and the PS decoder (including the upmix step) are typically time domain coupled.

In other embodiments of the invention described in connection with the drawings, L/R to M/S conversion is performed in the oversampled frequency domain (eg, QMF) or in the critically sampled frequency domain (eg, MDCT).

The third aspect of the application relates to a method for encoding a stereo signal into a bitstream signal. The method performs operations similar to the encoder system discussed above. Thus, the above remarks regarding the encoder system basically also apply to the encoding method.

The fourth aspect of the application relates to a method for decoding a bitstream signal including PS encoding parameters to generate a stereo signal. The method performs operations in the same way as the decoder system discussed above. Thus, the above remarks related to the decoder system basically also apply to the decoding method.

The invention is explained below by means of illustrative examples with reference to the accompanying drawings, where

fig. 1 illustrates one embodiment of an encoder system where, optionally, PS encoding parameters facilitate psychoacoustic control in a perceptual stereo encoder;

fig. 2 shows one embodiment of a PS encoder;

fig. 3 shows one embodiment of a decoder system;

fig. 4 shows one further embodiment of a PS encoder including a detector for deactivating PS encoding if L/R encoding is preferred;

fig. 5 shows one embodiment of a conventional PS encoder system including an additional SBR encoder for the downmix signal;

fig. 6 shows one embodiment of an encoder system comprising an additional SBR encoder for the downmix signal;

fig. 7 shows one embodiment of an encoder system comprising an additional SBR encoder in the stereo region;

fig. 8a-8d are different time-frequency representations of one of the two output channels at the output of the decoder;

fig. 9a shows one embodiment of a basic encoder;

fig. 9b shows one embodiment of an encoder that allows switching between linear prediction domain coding (typically for mono signals only) and transform domain coding (typically for both mono and stereo signals);

fig. 10 shows one embodiment of an encoder system;

fig. 11a is part of one embodiment of an encoder system;

fig. 11b is an exemplary implementation of the embodiment of the invention of FIG. 11a;

fig. 11c shows an alternative to the embodiment of FIG. 11a;

fig. 12 shows one embodiment of an encoder system;

fig. 13 shows one embodiment of a stereo encoder forming part of the encoder system of FIG. 12;

fig. 14 shows one embodiment of a decoder system for decoding a bitstream signal generated by the encoder system of FIG. 6;

fig. 15 shows one embodiment of a decoder system for decoding a bitstream signal generated by the encoder system of FIG. 7;

fig. 16a is part of one embodiment of a decoder system;

fig. 16b is an exemplary implementation of the embodiment of the invention of FIG. 16a;

fig. 16c is an alternative to the embodiment of the invention of FIG. 16a;

fig. 17 shows one embodiment of an encoder system; And

fig. 18 shows one embodiment of a decoder system.

In FIG. 1 shows an embodiment of an encoder system that combines PS coding using residual signal and adaptive perceptual stereo L/R or M/S coding. This embodiment of the invention is only an illustration of the principles of the present application. It should be understood that modifications and variations of this embodiment of the invention will be apparent to those skilled in the art. The encoder system includes a PS encoder 1 that receives an L, R stereo signal. PS encoder 1 contains a downmix stage for generating downmixed DMX and residual RES signals based on the L, R stereo signal. This operation can be described using a matrix H ^{− 1} downmix H ^–1 of size 2x2 that converts the L and R signals into a downmixed DMX signal and a residual RES signal:

.

.

Typically, the matrix H ^–1 is frequency dependent or time dependent, i.e. the elements of the H ^-1 matrix change with frequency and change from one time quantum to another. The H ^-1 matrix may be updated with each frame (eg, every 21 or 48 ms) and may have a frequency resolution of multiple bands, such as 28, 20, or 10 bands (called "parameter bands") on a perceptually oriented frequency scale (such as the Bark scale). ).

The elements of the H ^–1 matrix depend on the time- and frequency-dependent PS encoding parameters: IID (intensity difference between channels; also called CLD - channel level difference) and ICC (cross-correlation between channels). To determine PS encoding parameters 5, such as IID and ICC, PS encoder 1 includes a parameter determination step. An example of calculating the matrix elements of the inverse matrix H has the following form and is described in the MPEG Surround standard specification, document ISO/IEC 23003-1, subclause 6.5.3.2, which is incorporated herein by reference:

,

,

Where

, и

,

, And

,

Where

,

,

.and where

.

In addition, the encoder system includes a conversion step 2 that converts the downmix signal DMX and the residual signal RES from the PS encoder 1 into a pseudo-stereo signal L _p , R _p , for example, according to the following equations:

.

.

. Для

два уравнения псевдо-стереофонического сигнала L_p, R_p можно переписать как:In the above equations, the normalization gain g has, for example, the value

. For

the two pseudo-stereo signal equations L _p , R _p can be rewritten as:

.

.

The pseudo stereo signal L _p , R _p is then fed to the perceptual stereo encoder 3 which adaptively selects between stereo L/R coding and stereo M/S coding. M/S coding is a form of joint stereo coding. L/R coding may also be based on some aspect of joint coding, for example, the bits for the L and R channels may be jointly allocated from a common bit store.

The choice between stereo L/R or M/S encoding is preferably frequency dependent, ie. some frequency bands may be L/R encoded while other frequency bands may be M/S encoded. One implementation of the choice between stereo L/R or M/S encoding is described in "Sum-Difference Stereo Transform Coding", J. D. Johnston et al., IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP) 1992 , pages 569-572. The discussion of the choice between stereo L/R or M/S encoding in this document, in particular sections 5.1 and 5.2, is incorporated by reference herein.

Based on the pseudo-stereo signal L _p , R _{p ,} the perceptual encoder 3 can internally calculate the (pseudo-) middle/side signals M _p , S _p . These signals essentially correspond to the downmix DMX signal and the residual RES signal (except in the case of a possibly different gain). Then, if perceptual encoder 3 chooses to M/S-code a frequency band, then perceptual encoder 3 essentially encodes for that frequency band the downmix signal DMX and the residual signal RES (except in the case of a possibly different gain) as can also be performed in a conventional perceptual encoder system using conventional PS coding with a residual signal. The PS encoding parameters 5 and the output bit stream 4 of the perceptual encoder 3 are multiplexed into a single bit stream 6 by means of a multiplexer 7.

In addition to PS encoding the stereo signal, the encoder system of FIG. 1, as will be described below, allows L/R encoding of a stereo signal. As discussed above, the elements of the encoder downmix matrix H ^–1 (as well as the elements of the upmix matrix H used in the decoder) depend on the time- and frequency-dependent PS encoding parameters: IID (intensity difference between channels; also called CLD - difference channel levels) and ICC (cross-correlation between channels). An example of calculating the matrix elements of the upmix matrix H is described above. In the case of residual signal coding, the right column of the 2x2 upmix matrix H is:

.

.

However, instead, the right column of the 2×2 matrix H should preferably be modified as

.

.

The left column is preferably calculated as given in the MPEG Surround specification.

The modification of the right column of the upmix matrix H ensures that at IID = 0 dB and ICC = 0 (i.e. in the case when for the corresponding band the stereo channels L and R are independent and have the same level), the following matrix is obtained for the band H upmix:

.

.

It should be noted that the upmix matrix H as well as the downmix matrix H ^-1 are generally frequency dependent and time dependent. Thus, the values of the matrices are different for different time/frequency tiles (the tile corresponds to the intersection of a specific frequency band and a specific time period). In the case above, the downmix matrix H ^-1 is identical to the upmix matrix H. Thus, the pseudo-stereo signal L _p , R _p for a band can be calculated from the following equation:

.

.

Thus, in this case, PS coding with a residual signal using a downmix matrix H ^-1 followed by generation of a pseudo L/R signal in transform step 2 corresponds to an identity matrix and does not change the stereo signal at all for the corresponding frequency band, i.e. .e.

.

.

In other words, the conversion step 2 compensates the downmix matrix H ^-1 so that the pseudo-stereo signal L _p , R _p corresponds to the input stereo signal L, R.

This allows the original stereo input signal L, R to be encoded by a perceptual encoder 3 for a particular band. When L/R encoding is selected by the perceptual encoder 3 to encode a particular band, the encoder system behaves as a perceptual L/R encoder for encoding the L, R stereo input band.

The encoder system of FIG. 1 allows smooth adaptive switching between L/R coding and PS coding with residual signal in a frequency- and time-dependent manner. The encoder system avoids discontinuities in the waveform when switching between encoding schemes. This prevents artifacts from appearing. In order to achieve smooth transitions to the elements of the matrix H ^–1 in the encoder and the matrix H in the decoder for discrete values between two modifications of the stereo parameters, linear interpolation can be applied.

In FIG. 2 shows one embodiment of the PS encoder 1. The PS encoder 1 includes a downmix step 8 which, based on the stereo signal L, R, generates a downmix DMX signal and a residual signal RES. In addition, the PS encoder 1 includes a parameter estimation step 9 for estimating the PS encoding parameters 5 based on the stereo signal L, R.

In FIG. 3 shows one embodiment of a corresponding decoder system configured to decode bitstream 6 generated by the encoder system of FIG. 1. This embodiment of the invention is only an illustration of the principles of the present application. It should be understood that modifications and variations of this embodiment of the invention will be apparent to those skilled in the art. The decoder system includes a demultiplexer 10 for separating the PS encoding parameters 5 and the audio bitstream 4 generated by the perceptual encoder 3. The audio bitstream 4 is supplied to the perceptual stereo decoder 11, which is capable of selectively decoding the L/R encoded bitstream, or M/S-encoded audio bitstream. The operations of the decoder 11 are inverse to those of the encoder 3. Like the perceptual encoder 3, the perceptual decoder 11 preferably allows a frequency-dependent and a time-dependent coding scheme to be implemented. Some frequency bands L/R encoded by encoder 3 are L/R decoded by decoder 11, while other frequency bands M/S encoded by encoder 3 are M/S decoded by decoder 11. Decoder 11 outputs the pseudo-stereo signal L _p , R _p , which was previously input to the perceptual encoder 3. The pseudo-stereo signal L _p , R _p received from the perceptual decoder 11 is converted back into the downmixed DMX signal and the residual signal RES by step 12 L/R to M/S conversions. The operations of L/R to M/S conversion step 12 on the decoder side are inverse to those of the conversion step 2 on the encoder side. Preferably, conversion step 12 determines the downmix signal DMX and the residual signal RES according to the following equations:

.

.

.In the equations above, the normalization gain g is identical to the normalization gain g at the encoder side and, for example, has the value

.

The downmix signal DMX and the residual signal RES are then processed by the PS decoder 13 to obtain the final L and R output signals. converts the downmixed DMX signal and the residual RES signal back into the L and R channels:

.

.

The calculation of the elements of the upmix matrix H has already been discussed above.

The PS encoding and PS decoding processes in the PS encoder 1 and PS decoder 13 are preferably carried out in the oversampled frequency domain. For upstream time-frequency conversion with respect to the PS encoder, a hybrid complex-valued filter bank containing a QMF (Quadrature Mirror Filter) and a Nyquist filter, such as, for example, the filter bank described in the MPEG Surround standard, can be used (see ISO/IEC document 23003-1). The complex QMF representation of the signal is resampled by a factor of 2 because it is complex-valued and not real-valued. This allows time and frequency adaptive signal processing without audible aliasing artifacts. This hybrid filter bank typically provides high frequency resolution (narrow band) at low frequencies, while at high frequencies multiple QMF bands are grouped into a wider band. Article "Low Complexity Parametric Stereo Coding in MPEG-4", H. Purnhagen, Proc. of the 7th Int. Conference on Digital Audio Effects (DAFx'04), Naples, Italy, October 5-8, 2004, pages 163-168, describes an embodiment of a hybrid filter bank (see section 3.2 and FIG. 4). This disclosure is incorporated herein by reference. The referenced document allows a sampling rate of 48 kHz with a (nominal) bandwidth from a 64-band QMF block of 375 Hz. Bark's perceptual frequency scale, however, requires a bandwidth of approximately 100 Hz for frequencies below 500 Hz. Therefore, the first 3 QMF bands can be split into even narrower subbands by means of a Nyquist filter bank. The first QMF band can be split into 4 bands (plus two more for negative frequencies), and the second and third QMF bands can be split into two bands each.

On the other hand, adaptive L/R or M/S coding is preferably performed in the region of the critically sampled MDCT (as described, for example, in AAC) in order to provide an efficient representation of the quantized signal. The conversion of the downmix signal DMX and the residual signal RES into a pseudo-stereo signal L _p , R _p in the conversion step 2 can be done in the time domain since the PS encoder 1 and the perceptual encoder 3 can in any case be coupled in the time domain. In the decoding system, the perceptual stereo decoder 11 and the PS decoder 13 are also preferably coupled in the time domain. Therefore, the conversion of the pseudo-stereo signal L _p , R _p into the downmix signal DMX and the residual signal RES in the conversion step 12 can also be performed in the time domain.

An adaptive stereo L/R or M/S encoder such as encoder 3 in FIG. 1 is typically a perceptual audio encoder that incorporates a psychoacoustic model to enable high-efficiency encoding at low bit rates. An example of such an encoder is an AAC encoder that uses MDCT critically sampled domain transform coding in combination with time- and frequency-dependent quantization that is driven using a psychoacoustic model. In addition, the time- and frequency-dependent decision to choose between L/R and M/S encoding is typically driven by perceptual entropy criteria that are computed using a psychoacoustic model.

A perceptual stereo encoder (such as encoder 3 in FIG. 1) operates on a pseudo-stereo L/R signal (see L _p , R _p in FIG. 1). In order to optimize the coding efficiency of the stereo encoder (in particular, so that it makes the right choice between L/R encoding and M/S encoding), modification of the psychoacoustic control mechanism (including the control mechanism deciding between stereo L /R encoding and stereo M/S encoding, a control mechanism that controls the time- and frequency-dependent quantization) in the perceptual stereo encoder so that it takes into account signal modifications (pseudo-L/R conversion to DMX and RES followed by PS encoding) that are applied in the decoder when generating the final L, R stereo output signal. These signal modifications can affect the binaural masking effects that are exploited by the psychoacoustic control mechanisms. Therefore, psychoacoustic control mechanisms should preferably be suitably adapted. For this, it may be useful for psychoacoustic control mechanisms to have access not only to the pseudo-L/R signal (see L _p , R _p in Fig. 1), but also to the PS encoding parameters (see position 5 in Fig. 1) and/or the original L, R stereo signal. The access of the psychoacoustic control mechanisms to the PS encoding parameters and the L, R stereo signal is shown in FIG. 1 dashed line. For example, masking threshold(s) can be adapted based on this information.

An alternative approach to optimizing psychoacoustic control is to add to the encoder system a deactivation step detector that has the ability to effectively deactivate PS encoding when needed, preferably in a time and frequency dependent manner. Deactivating PS encoding is appropriate, for example, when stereo L/R encoding is expected to be more useful, or when psychoacoustic control may have difficulty encoding the pseudo-L/R signal effectively. PS encoding can be effectively deactivated by specifying the downmix matrix H ^-1 such that the downmix matrix H ^-1 with subsequent transformation (see step 2 in FIG. 1) corresponds to the identity matrix (i.e., the matching operation) or identity matrix multiplied by some factor. For example, PS encoding can be effectively disabled by forcing the PS encoding parameters IID = 0 dB and ICC = 0. In this case, as discussed above, the pseudo-stereo signal L _p , R _p corresponds to the stereo signal L, R.

Said modification control of PS encoding parameters by the detector is shown in FIG. 4. In this case, the detector 20 receives the PS encoding parameters 5 determined by the parameter estimation step 9 . When the detector does not deactivate the PS encoding, the detector 20 passes the PS encoding parameters to the downmix step 8 and to the multiplexer 7, i.e. in this case, the PS encoding parameters 5 correspond to the PS encoding parameters 5' supplied to the downmix step 8. In the event that the detector detects that the PS encoding is unfavorable and should be deactivated (for one or more frequency bands), the detector modifies the affected PS encoding parameters 5 (eg, sets the PS encoding parameters, IID and/or ICC, to IID = 0 dB and ICC = 0) and feeds the modified PS encoding parameters 5' to the downmix step 8. The detector may optionally also take into account the left and right signals L, R to decide whether to modify the PS encoding parameters (see dashed lines in FIG. 4).

In the following figures, the term QMF (quadrature mirror filter or filter bank) also includes the QMF subband filter bank in combination with the Nyquist filter bank, i.e. design of the hybrid filter unit. In addition, all quantities in the following description may be frequency dependent, for example, different downmix and upmix matrices may be derived for different frequency ranges. In addition, the residual signal encoding may cover only a portion of the usable audio frequency band (ie, the residual signal is encoded for only a portion of the usable audio frequency band). The downmixing aspects described below for some frequency bands may appear in the QMF domain (e.g., in accordance with the prior art), while for other frequency bands only, for example, the phase aspects will be in the complex QMF domain, and the conversion amplitude will be produced in the real-valued MDCT region.

In FIG. 5 shows a conventional PS encoder system. Each of the stereo channels L, R is first analyzed by a complex QMF of 30 with M subbands, eg a QMF with M=64 subbands. The subband signals are used in the PS encoder 31 to estimate the PS encoding parameters 5 and the downmix DMX signal. The downmix DMX signal is used in the SBR encoder 32 to estimate the SBR (spectral band replication) parameters 33 . The SBR encoder 32 extracts SBR parameters 33 representing the spectrum envelope of the original highband signal, possibly combined with noise and tone criteria. Unlike the PS encoder 31, the SBR encoder 32 does not affect the signal passing to the base encoder 34. The DMX downmix of the PS encoder 31 is synthesized using inverse QMF 35 with N subbands. For example, a complex QMF with N=32 can be used where only the 32 lowest subbands out of the 64 subbands used by PS encoder 31 and SBR encoder 32 are synthesized. passes to the core encoder 34 a time domain signal containing half the bandwidth of the input signal. Due to the reduced bandwidth, the sampling rate may be reduced by half (not shown). Core encoder 34 converts the perceptual encoding of the mono input signal to generate bitstream 36. The PS encoding parameters are embedded in bitstream 36 using a multiplexer (not shown).

In FIG. 6 shows a further embodiment of an encoder system that combines PS coding using a residual signal with a stereo core encoder 48, where the stereo core encoder 48 is suitable for adaptive perceptual stereo L/R and M/S coding. This embodiment of the invention is only an illustration of the principles of the present application. It should be understood that modifications and variations of this embodiment of the invention will be apparent to those skilled in the art. The L, R input channels representing the original left and right channels are analyzed by the complex QMF 30 in a manner similar to that discussed in connection with FIG. 5. In contrast to the PS encoder 31 of FIG. 5, the PS encoder 41 of FIG. 6 not only outputs the downmixed DMX signal, but also outputs the residual RES signal. The downmixed DMX signal is used by the SBR encoder 32 to determine the SBR parameters 33 of the downmixed DMX signal. In conversion step 2, a fixed DMX/RES to pseudo-L/R conversion (eg, M/S to L/R conversion) is applied to the downmixed DMX and residual RES signals. Step 2 of the conversion in FIG. 6 corresponds to conversion step 2 in FIG. 1. Transform step 2 generates the "pseudo" left and right channel signal L _p , R _p to be operated on by core encoder 48. In this embodiment, an inverse L/R to M/S transform is applied in the QMF domain prior to subband synthesis. filter banks 35. Preferably, the number N (eg, N=32) of subbands for synthesis corresponds to half the number of M (eg, M=64) subbands used for analysis, and core encoder 48 operates at half the sample rate. It should be noted that there is no limit to using 64 subband channels for QMF analysis in the encoder and 32 subbands for synthesis, and other values are possible depending on what sampling rate is desired for the signal received by the core encoder 48. Basic stereo encoder 48 performs perceptual encoding of the filter bank signal 35 to generate a bitstream signal 46 . The PS encoding parameters 5 are embedded in the bitstream signal 46 by a multiplexer (not shown). Optionally, the base encoder 48 may use the PS encoding parameters and/or the original L/R input signal. This information indicates to the base encoder 48 how the PS encoder 41 rotates in stereo space. This information may guide core encoder 48 on how to manage quantization in a perceptually optimal manner. This is shown in FIG. 6 dashed lines.

In FIG. 7 shows a further embodiment of an encoder system that is similar to the system of FIG. 6. In contrast to the embodiment of the invention according to FIG. 6, in FIG. 7, the SBR encoder 42 is attached in the upstream direction relative to the PS encoder 41. In FIG. 7, the SBR encoder 42 is placed in front of the PS encoder 41 and thus performs operations on the left and right channels (in this case, in the QMF region) instead of, as in FIG. 6, perform operations on the downmixed DMX signal.

Due to the permutation of the SBR encoder 42, the PS encoder 41 may be configured to operate not over the entire bandwidth of the input signal, but, for example, only at a frequency range below the SBR transition frequency. In FIG. 7, the SBR parameters 43 for the SBR band are in stereo space, and the output of the corresponding PS decoder, as will be discussed later in connection with FIG. 15 generates an original stereo frequency band for operation by the SBR decoder. This modification, ie. attaching the SBR encoder module 42 in the upstream direction relative to the PS encoder module 41 in the encoder system, and accordingly placing the SBR decoder module after the PS decoder in the decoder system (see FIG. 15), has the advantage that , which can reduce the use of a decorrelated signal to generate a stereo output signal. It should be noted that if there is no or no residual signal for a particular frequency band, the PS decoder uses a decorrelated version of the downmixed DMX signal instead. However, the reconstruction based on the decorrelated signal reduces the sound quality. Therefore, reducing the use of the decorrelated signal leads to an increase in audio quality.

This advantage of the embodiment of the invention according to FIG. 7 compared to the embodiment of the invention of FIG. 6 will be described in more detail with reference to FIG. 8a-8d.

In FIG. 8a shows the time-frequency representation of one of the two output channels L, R (on the decoder side). In the case of FIG. 8a, an encoder is used where the PS encoding module is placed before the SBR encoding module, as in the encoder of FIG. 5 or FIG. 6 (in the decoder, the PS decoder is placed after the SBR decoder, see FIG. 14). In addition, the residual signal is encoded only in the low bandwidth frequency band 50, which is smaller than the base encoder frequency band 51. As seen from the visualization of Fig. 8a, frequency range 52, where the decorrelated signal to be used by the PS decoder covers the entire frequency range except for the lower frequency range 50 covered by using the residual signal. In addition, the SBR covers a frequency range of 53 that starts much higher than the decorrelated signal's frequency range. Thus, the entire frequency range is divided into the following frequency ranges: in the lower frequency range (see range 50 in Fig. 8a), waveform coding is used; in the middle frequency range (see the area of intersection of frequency ranges 51 and 52), waveform coding is used in combination with a decorrelated signal; and in the higher frequency band (see frequency band 53) a regenerated SBR signal regenerated from lower frequencies is used in combination with a decorrelated signal which is generated by the PS decoder.

In FIG. 8b, a time-frequency representation of one of the two output channels L, R (at the decoder side) is rendered for the case where the SBR encoder is attached upstream of the PS encoder in the encoder system (and the SBR decoder is located after the PS decoder in the decoder system). ). In FIG. 8b shows a low bit rate scenario where the residual signal bandwidth 60 (where the residual signal is coded) is below the bandwidth of the core encoder 61. Since the SBR decoding process is performed on the decoder side after the PS decoder (see FIG. 15), the residual signal used for the low frequencies is also used to reconstruct at least a portion (see frequency band 64) of the higher frequencies in the 63 SBR band.

This advantage becomes even more pronounced when operating at intermediate bit rates, where the residual signal bandwidth approaches or becomes equal to the bandwidth of the base encoder. In this case, the time-frequency representation of FIG. 8a (using the order of PS encoding and SBR encoding of FIG. 6) results in the time-frequency representation shown in FIG. 8s. In FIG. 8c, the residual signal covers substantially the entire low-band range 51 of the core encoder; in the 53 SBR frequency band, the PS decoder uses a decorrelated signal. In FIG. 8d visualizes the time-frequency representation in the case of the preferred order of encoder/decoder modules (i.e., SBR encoding is performed on the stereo signal before PS encoding, as shown in FIG. 7). In this case, the PS decoding module in the decoder performs operations before the SBR decoding module, as shown in FIG. 15. Thus, the residual signal is part of the low frequency band used for the high frequency reconstruction. When the bandwidth of the residual signal becomes equal to the bandwidth of the downmixed mono signal, no decorrelated signal information is needed for the output decoder (see full frequency range, which is shaded in FIG. 8d).

In FIG. 9a shows an embodiment of a basic stereo encoder 48 with adaptive selection of stereo L/R or M/S coding in the MDCT transform domain. Said stereo encoder 48 may be used in FIG. 6 and 7. The basic mono encoder 34 shown in FIG. 5 can be seen as a special case of the basic stereo encoder 48 of FIG. 9a, in which only one mono input channel is processed (i.e., when there is no second input channel, shown in dashed line in FIG. 9a).

In FIG. 9b shows a more general encoder. For mono signals, the coding may switch between linear prediction domain coding (see block 71) and transform domain coding (see block 48). This type of encoder introduces several coding methods that can be used adaptively depending on the characteristics of the input signal. In this case, the encoder can choose between encoding the signal using encoder 48 with an AAC-type transform (suitable for mono and stereo signals, with adaptive selection of L/R or M/S encoding in the case of stereo signals) and using encoder 71 of the AMR-WB+ (Adaptive Multi Rate - WideBand Plus) type, suitable for mono signals only. The core AMR-WB+ encoder 71 evaluates the residual signal of the linear predictor 72 and in turn also chooses between the transform coding approach of the linear prediction residual signal and the classic ACELP (Algebraic Code Excited Linear Prediction) speech encoder approach for encoding the linear prediction residual signal. To select between AAC-type transform encoder 48 and AMR-WB+ type core encoder 71, a mode selection decision step 73 is used, which decides between encoders 48 and 71 based on the input signal.

Encoder 48 is an AAC-type MDCT-based encoder. If the mode decision step 73 directs the input signal to use MDCT-based coding, the signals, the mono input signal or the stereo input signals, are encoded by the AAC-based MDCT encoder 48 . MDCT encoder 48 performs MDCT analysis of one or two signals in MDCT steps 74. In the case of a stereo signal, step 75 also makes M/S or L/R selection based on bandwidth before quantization and encoding. Stereo L/R coding or stereo M/S coding is selected in a frequency dependent manner. Step 75 also performs L/R to M/S conversion. If an M/S encoding decision is made for a particular frequency band, step 75 outputs an M/S signal for that frequency band. Otherwise, step 75 outputs an L/R signal for that frequency band.

Thus, if a transform coding mode is used, the stereo coding function of the underlying base encoder can be used for the stereo signal with full efficiency.

If the mode decision step 73 sends the mono signal to the encoder 71 in the linear prediction domain, the mono signal is then analyzed by linear prediction analysis in block 72. It is then decided to encode the LP residual signal by the ACELP-type encoder 76 in the time domain or by the encoder 77 of the TCX (Transform Coded eXcitation) type, which performs operations in the MDCT region. The linear prediction encoder 71 does not have any inherent stereo coding capability. Therefore, in order to allow the encoder 71 in the linear prediction domain to encode a stereo signal, an encoder configuration similar to that shown in FIG. 5. In this configuration, the PS encoder generates PS encoding parameters 5 and a downmixed mono DMX signal, which is then encoded in the linear prediction domain by the encoder.

In FIG. 10 shows a further embodiment of an encoder system, where the parts of FIG. 7 and FIG. 9 combined in a new way. The DMX/RES to pseudo-L/R conversion unit 2 described in FIG. 7 is located within the AAC-type downstream encoder 70 prior to the stereo MDCT analysis step 74. This embodiment has the advantage that the 2 DMX/RES to pseudo-L/R conversion is applied only when a basic stereo MDCT encoder is used. Therefore, when the transform coding mode is used, the full performance of the stereo coding function of the underlying core encoder can be used to stereo code the frequency range covered by the residual signal.

While the mode selection decision step 73 of FIG. 9b performs operations on both the mono input signal and the stereo input signal, the decision step 73' of FIG. 10 performs operations on the downmix signal DMX and the residual signal RES. In the case of a mono input signal, the mono signal can be directly used as a DMX signal, the RES signal can be set to zero, and the default PS encoding parameters can be set to IID = 0 dB and ICC = 1.

If the mode decision step 73' sends the downmixed DMX signal to the encoder 71 in the linear prediction region, the downmixed DMX signal is then analyzed by linear prediction analysis in block 72. It is then decided whether to encode the residual LP signal by the encoder 76 ACELP- type in the time domain, or by means of an encoder 77 of the TCX (Transform Coded eXcitation) type, which performs operations in the MDCT domain. The linear prediction encoder 71 does not have any inherent stereo coding capability that could be used to encode the residual signal in addition to the downmixed DMX signal. Therefore, when encoding the downmixed DMX signal by the encoder 71 in the linear prediction region, a dedicated residual signal encoder 78 is used to encode the residual signal RES. This encoder may, for example, be a mono AAC encoder.

It should be noted that the encoders 71 and 78 of FIG. 10 can be omitted (in which case the mode decision step 73' is no longer necessary).

In FIG. 11a shows details of a further, alternative embodiment of an encoder system that achieves the same advantages as the embodiment of the invention of FIG. 10. In contrast to the embodiment of FIG. 10 in FIG. 11a, the DMX/RES to pseudo-L/R transform 2 is placed after the MDCT analysis 74 of the base encoder 70, i. e. the transformation is performed in the MDCT region. The transform in block 2 is linear and time independent and can therefore be placed after the MDCT analysis 74. The remaining blocks of FIG. 10 which are not shown in FIG. 11 may optionally be added in the same way as in FIG. 11a. Alternatively, the MDCT analysis blocks 74 may also be placed after the transform block 2.

In FIG. 11b illustrates one implementation of the embodiment of the invention of FIG. 11a. In FIG. 11b shows an exemplary implementation of step 75 of selecting between M/S encoding and L/R encoding. Step 75 includes a sum and difference conversion step 98 (more specifically, an L/R to M/S conversion step) that receives a pseudo-stereo signal L _p , R _p . The transform step 98 generates a pseudo-mid/side signal M _p , S _p by performing an L/R to M/S transform. Except for possible gain, the following equations apply: M _p =DMX, S _p =RES.

Step 75 decides between L/R encoding and M/S encoding. Based on the selection made, either the pseudo-stereo signal L _p , R _p , or the pseudo-middle/side signal M _p , S _p is selected (see selector switch), which is encoded in block 97 of the AAC. It should be noted that two AAC blocks 97 (not shown in FIG. 11b) can also be used, where the first AAC block 97 is for the pseudo stereo signal L _p , R _p , and the second AAC block 97 is for the pseudo mid/side signal. M _p , S _p . In this case, the choice of L/R or M/S is made by selecting either the output signal of the first block 97 AAC, or the output signal of the second block 97 AAC.

In FIG. 11c shows an alternative embodiment of the invention of FIG. 11a. In this case, step 2 of the transformation is not explicitly used. Instead, the conversion step 2 and step 75 are combined into a single step 75'. The downmix signal DMX and the residual signal RES are fed to a sum and difference conversion step 99 (more precisely, a DMX/RES to pseudo-L/R conversion step), which is part of step 75'. The conversion step 99 generates a pseudo-stereo signal L _p , R _p . The DMX/RES to pseudo-L/R conversion step 99 of FIG. 11c is similar to L/R to M/S conversion step 98 of FIG. 11b (except possibly for a different gain). However, in FIG. 11c, the choice between M/S decoding and L/R decoding needs to be inverted with respect to FIG. 11b. It should be noted that in FIG. 11b and 11c, the switch position for selecting L/R or M/S is shown at the L _p /R _p position, which is the top position in FIG. 11b and lower - in FIG. 11s. This visualizes the idea of the inverse meaning of choosing L/R or M/S.

It should be noted that in FIG. 11b and 11c, there is preferably a separate switch for each frequency band in the MDCT region, and thus the choice between L/R and M/S can be either time dependent or frequency dependent. In other words, the switch position preferably depends on the frequency. The conversion steps 98 and 99 may convert the entire usable frequency range or only one frequency band.

Also, note that all blocks 2, 98, and 99 can be referred to as "sum-and-difference transformation blocks" because these blocks all implement a transformation matrix of the form

.

.

The only thing that can be different in blocks 2, 98, 99 is the gain c.

ниже) и OPD (общую разность фаз, см. 

ниже), которые позволяют характеризовать фазовое соотношение между двумя каналами, L и R, стереофонического сигнала. Пример этих фазовых параметров приведен в стандарте ISO/IEC 14496-3, подпункт 8.6.4.6.3, который ссылкой включается в настоящее описание. При использовании фазовых параметров результирующая матрица

повышающего микширования (и обратная ей матрица

) становится комплекснозначной в соответствии с уравнением:In FIG. 12 describes the following embodiment of an encoder system. It uses an extended set of PS encoding parameters, which, in addition to IID and ICC (described above), includes two more parameters: IPD (Inter-Channel Phase Difference, see below).

below) and OPD (Total Phase Difference, see

below) that characterize the phase relationship between two channels, L and R, of a stereo signal. An example of these phase parameters is given in ISO/IEC 14496-3, subclause 8.6.4.6.3, which is incorporated herein by reference. When using phase parameters, the resulting matrix

upmix (and its inverse matrix

) becomes complex-valued according to the equation:

,

,

Where

,

,

and where

.

.

The PS encoder step 80, which performs operations in the complex QMF domain, takes into account only the phase dependencies of the L, R channels. ^–1 ) is taken into account in the MDCT domain, which is part of the basic stereo encoder 81. Therefore, the phase dependencies between the two channels are extracted in the complex QMF domain, while the remaining real-valued waveform dependencies are extracted in the real-valued domain of the critically sampled MDCT, which is part of the the stereo encoding mechanism of the base encoder used. This has the advantage that the extraction of linear relationships between channels can be tightly integrated into the base encoder's stereo coding (although, to prevent aliasing, in the critically sampled MDCT region, only for the frequency range covered by the residual coding, possibly minus "guard band" on the frequency axis).

регулирования фазы, которую он генерирует, может соответствовать следующему уравнению:Step 80 of adjusting the phase of the PS encoder of FIG. 12 extracts phase-related PS encoding parameters, such as IPD (inter-channel phase difference) and OPD (total phase difference) parameters. Therefore, the matrix

the phase control that it generates can correspond to the following equation:

.

.

с отрегулированной фазой в области MDCT. Этот сигнал подвергается понижающему микшированию на этапе 82 понижающего микширования посредством матрицы

низводящего вращения, которая, как обсуждалось выше, представляет собой действительнозначную часть комплексной матрицы

понижающего микширования, и, таким образом, генерируются низведенный сигнал DMX и остаточный сигнал RES. За операцией понижающего микширования следует преобразование L/R в M/S согласно настоящей заявке (см. этап 2 преобразования), и, таким образом, генерируется псевдо-стереофонический сигнал L_p, R_p. Псевдо-стереофонический сигнал L_p, R_p обрабатывается посредством алгоритма стереофонического кодирования (см. адаптивный стереофонический M/S- или L/R-кодер 83), в данном конкретном варианте осуществления изобретения механизм стереофонического кодирования, который зависит от критериев перцептуальной энтропии, принимает решение о кодировании L/R-представления сигнала или M/S-представления сигнала. Это решение предпочтительно зависит от времени и от частоты.As discussed above, the down-rotation portion of the PS encoding unit deals with the stereo encoding unit 81 of the core encoder of FIG. 12. A stereo encoding unit 81 that performs operations in the MDCT region is shown in FIG. 13. The stereo encoding module 81 receives a stereo signal

with adjusted phase in the MDCT region. This signal is downmixed in a downmix step 82 by a matrix

descending rotation, which, as discussed above, is the real-valued part of the complex matrix

downmix, and thus a downmixed DMX signal and a residual RES signal are generated. The downmix operation is followed by L/R to M/S conversion according to the present application (see conversion step 2), and thus a pseudo-stereo signal L _p , R _p is generated. The pseudo-stereo signal L _p , R _p is processed by a stereo coding algorithm (see adaptive stereo M/S or L/R encoder 83), in this particular embodiment, a stereo coding engine that depends on perceptual entropy criteria adopts deciding whether to encode the L/R representation of the signal or the M/S representation of the signal. This solution preferably depends on time and frequency.

In FIG. 14 shows an embodiment of a decoder system that is suitable for decoding bitstream 46 generated by the encoder system shown in FIG. 6. This embodiment of the invention is only an illustration of the principles of the present application. It should be understood that modifications and variations of this embodiment of the invention will be apparent to those skilled in the art. The base decoder 90 decodes the bit stream 46 into pseudo-left and pseudo-right channels, which are converted into the QMF region by filter banks 91. Then, in a conversion step 12, the received pseudo-stereo signal L _p , R _p is converted from L/R to DMX/ RES, and thus a downmixed DMX signal and a residual RES signal are created. When using SBR encoding, these signals are low-band signals, for example, the DMX downmix and the RES residual can only contain audio information for the low band up to about 8 kHz. The downmix DMX signal is used by the SBR decoder 93 to reconstruct the high frequency band based on the received SBR parameters (not shown). The output of the SBR decoder 93 (including the low and reconstructed high bands of the DMX downmix signal) and the residual signal RES are input to the PS decoder 94, which performs operations in the QMF region (in particular, in the QMF + Nyquist hybrid block region). The downmix DMX signal at the input of the PS decoder 94 also contains information about the audio signal in the high frequency band (for example, up to 20 kHz), while the residual signal RES at the input to the PS decoder 94 is a low-band signal (for example, limited frequency up to 8 kHz). Therefore, for the high frequency band (eg, the 8 kHz to 20 kHz band), the PS decoder 94 uses a decorrelated version of the downmix DMX signal instead of the bandlimited residual signal RES. Thus, the decoded signals at the output of the PS decoder 94 are based on the residual signal only up to 8 kHz. After PS decoding, both output channels of the PS decoder 94 are converted to the time domain by the filter banks 95, and thus a stereo L, R output signal is generated.

In FIG. 15 shows an embodiment of a decoding system that is suitable for decoding bitstream 46 generated by the encoder system of FIG. 7. This embodiment of the invention is solely illustrative of the principles of the present application. It should be understood that modifications and variations of this embodiment of the invention will be apparent to those skilled in the art. The principle of operation of the embodiment of the invention according to FIG. 15 is similar to the operation of the decoder system described in FIG. 14. In contrast to FIG. 14, SBR decoder 96 in FIG. 15 is located at the output of the PS decoder 14. In addition, the SBR decoder uses SBR parameters (shown) generating spectrum envelope data, unlike the mono SBR parameters of FIG. 14. The downmix and residual signals at the input of the PS decoder 94 are typically low-band signals, for example, the DMX downmix signal and the RES residual signal may only contain audio signal information for the low frequency band, for example, up to about 8 kHz. Based on the low-band DMX downmix signal and the RES residual signal, the PS encoder 94 determines a low-band stereo signal, eg up to about 8 kHz. Based on the low-bandwidth stereo signal and the SBR stereo parameters, the SBR decoder 96 reconstructs the high frequency portion of the stereo signal. Compared to the embodiment of the invention according to FIG. 14, the embodiment of the invention of FIG. 15 provides the advantage that a decorrelated signal is not required (see also FIG. 8d) and thus improved audio quality is achieved, while FIG. 14, a decorrelated signal is required for the high frequency part (see also FIG. 8c), thus degrading the sound quality.

In FIG. 16a shows an embodiment of a decoding system that is inverse to the coding system of FIG. 11a. The input bitstream signal is applied to the decoder section 100, which generates the first decoded signal 102 and the second decoded signal 103. At the decoder, M/S encoding or L/R encoding is selected. The choice is indicated in the received bitstream. Based on this information, in step 101, a selection of M/S or L/R is made. In case M/S is selected by the decoder, the first 102 and second 103 signals are converted to a (pseudo) L/R signal. In the event that L/R is selected by the decoder, the first 102 and second 103 signals may pass step 103 without being converted. The pseudo-L/R signal, L _p , R _p , at the output of step 101 is converted into a DMX/RES signal by a conversion step 12 (in this step, quasi L/R to M/S conversion is performed). Preferably, steps 100, 101 and 12 of FIG. 16a perform operations in the MDCT area. Conversion blocks 104 may be used to convert the downmixed DMX signal and the residual RES signal into the time domain. The received signal is then applied to a PS decoder (not shown) and optionally to an SBR decoder as shown in FIG. 14 and 15. Alternatively, blocks 104 may also be placed before block 12.

In FIG. 16b illustrates an implementation of the embodiment of the invention of FIG. 16a. In FIG. 16b shows an exemplary implementation of step 101 for selecting between M/S decoding and L/R decoding. Step 101 includes a sum and difference (M/S to L/R) transform step 105 that receives first 102 and second 103 signals.

Based on the encoding information provided in the bitstream, step 101 makes a choice between L/R encoding and M/S encoding. If a choice is made in favor of L/R encoding, then the output signal of the decoding block 100 is applied to the conversion step 12 .

In FIG. 16c shows an alternative to the embodiment of FIG. 16a. In this case, the conversion step 12 is not explicitly used. Instead, the conversion step 12 and step 101 are combined into a single step 101'. The first 102 and second 103 signals are applied to the sum and difference conversion stage 105' (more precisely, to the pseudo-L/R to DMX/RES conversion stage), which is part of the stage 101'. The conversion step 105' generates a DMX/RES signal. The conversion step 105' of FIG. 16c is similar to the transform step 105 of FIG. 16b or identical to it (except possibly for a different gain). In FIG. 16c, the choice between M/S decoding and L/R decoding needs to be inverted with respect to FIG. 16b. In FIG. 16c the switch is in the down position, while in FIG. 16b the switch is in the up position. This visualizes the inversion of the L/R or M/S selection (the selection signal can simply be inverted by means of an inverse converter).

It should be noted that in FIG. 16b and 16c, there is preferably an individual switch for each frequency band in the MDCT region, and thus the choice between L/R and M/S can be both time and frequency dependent. The conversion steps 105 and 105' may convert the entire usable frequency range or only a single frequency band.

In FIG. 17 shows a further embodiment of a coding system for encoding a stereo signal L, R into a bitstream signal. The coding system includes a downmix step 8 for generating a downmix DMX signal and a residual signal RES based on the stereo signal. In addition, the encoding system includes a parameter determination step 9 for determining one or more parametric stereo encoding parameters 5 . In addition, the encoding system includes means 110 perceptual encoding in the downstream direction relative to stage 8 downmixing. The following encoding modes are selectable:

- encoding, based on the sum signal of the downmix DMX signal and the residual signal RES and on the difference signal of the downmix DMX signal and the residual signal RES, or

- coding, based on the downmixed DMX signal and the residual RES signal.

Preferably, the selection is time and frequency dependent.

The encoding means 110 includes a sum-and-difference transform 111 which generates a sum and a difference signal. In addition, the encoding means 110 includes a selector 112 for selecting encoding based on the sum and difference signals, or based on the DMX downmix and the residual RES. In addition, a coding unit 113 is provided. Alternatively, two encoding units 113 may be used, where the first encoding unit 113 encodes the DMX and RES signals, and the second encoding unit 113 encodes the sum and difference signals. In this case, the selection block 112 is in the downstream direction with respect to the two encoding blocks 113 .

The sum-and-difference conversion block 111 has the form:

.

.

The transform block 111 may correspond to the transform block 99 of FIG. 11s.

The output of the perceptual encoder 110 is combined with the parameters 5 of the parametric stereo signal in the multiplexer 7 to form the resulting bit stream 6.

In contrast to the design of FIG. 17, encoding based on the downmix signal DMX and the residual signal RES can be realized by encoding the resultant signal which is generated by converting the downmix signal DMX and the residual signal RES through two successive sum and difference transformations as shown in FIG. 11b (see two conversion blocks 2 and 98). The resulting signal, after two sum-and-difference conversions, corresponds to the downmix DMX signal and the residual RES signal (except possibly for a different gain).

In FIG. 18 shows an embodiment of a decoder system which is the inverse of the encoder system of FIG. 17. The decoder system includes means 120 for perceptual decoding based on a bitstream signal. Before decoding, the PS encoding parameters are separated from the bitstream signal 6 in the demultiplexer 10. The decoding means 120 includes a base decoder 121 which (by decoding) generates a first signal 122 and a second signal 123. The decoding means outputs a downmixed DMX signal and a residual signal RES.

The downmix signal DMX and the residual signal RES are selectively

- based on the sum of the first signal 122 and the second signal 123 and on the difference between the first signal 122 and the second signal 123,

or

- based on the first signal 122 and the second signal 123.

Preferably, the selection is time and frequency dependent. The selection is made in selection step 125 .

The decoding means 120 includes a sum-and-difference transform 124 that generates the sum and difference signals.

The conversion to sum and difference in block 124 is of the form:

.

.

Transform block 124 may correspond to block 105' of FIG. 16s.

Once selected, the DMX and RES signals are fed to an upmix step 126 to generate a stereo L, R signal based on the downmixed DMX signal and the residual RES signal. The upmix operation depends on the PS encoding parameters 5 .

Preferably, the selection in FIG. 17 and 18 is frequency dependent. In FIG. 17, for example, time-to-frequency conversion (eg, by MDCT or analysis filter bank) may be performed as a first step in perceptual encoding means 110. In FIG. 18, for example, frequency-to-time conversion (eg, by inverse MDCT or synthesis filter bank) may be performed in the last step in perceptual decoding means 120.

It should be noted that in the embodiments described above, the signals, parameters, and matrices may be frequency dependent or frequency independent, and/or time dependent or time independent. The calculation steps described can be carried out for individual frequencies or for the entire bandwidth of the audio signal.

In addition, it should be noted that all the various transformations to sum and difference, i.e. DMX/RES to Pseudo L/R conversion, Pseudo L/R to DMX/RES conversion, L/R to M/S conversion, and M/S to L/R conversion, are of the form

.

.

The only thing that may differ is the gain c. Therefore, in principle, each of these transformations can be replaced by another transformation from among the indicated transformations. If the gain during the encoding process is not correct, it can be compensated during the decoding process. Also, if you place two identical or two different sum and difference transforms in series, the resulting transform will correspond to an identity matrix (perhaps multiplied by a gain).

In an encoder system including a PS encoder and an SBR encoder, various PS/SBR configurations are possible. In the first configuration shown in FIG. 6, the SBR encoder 32 is attached downstream of the PS encoder 41. In the second configuration shown in FIG. 7, the SBR encoder 42 is coupled upstream of the PS encoder 41. Depending on, for example, the desired target bit rate, properties of the core encoder, and/or one or more different factors, in order to provide the best performance, one configuration may be preferred over other configurations. Generally, for lower bit rates, the first configuration may be more preferable, while for higher bit rates, the second configuration may be more preferable. Therefore, it is desirable for the encoder system to support both of these configurations in order to be able to make a choice of the preferred configuration depending on, for example, the desired target bit rate and/or one or more other criteria.

In a decoder system including a PS decoder and an SBR decoder, various PS/SBR configurations are also possible. In the first configuration shown in FIG. 14, the SBR decoder 93 is connected in the upstream direction with respect to the PS decoder 94. In the second configuration shown in FIG. 15, the SBR decoder 96 is coupled downstream of the PS decoder 94. To achieve correct operation, the system configuration of the decoder must match the system configuration of the encoder. If the encoder is configured according to FIG. 6, the decoder is respectively configured according to FIG. 14. If the encoder is configured in accordance with FIG. 7, the decoder is respectively configured according to FIG. 15. In order to ensure correct operation, the encoder preferably signals to the decoder the PS/SBR configuration that has been selected for encoding (and thus the PS/SBR configuration that is to be selected for decoding). Based on this information, the decoder makes a selection of the proper decoder configuration.

As discussed above, in order to ensure correct operation of the decoder, there is preferably a mechanism for signaling from the encoder to the decoder the configuration to be used in the decoder. This may be done explicitly (eg, via a specialized bit or field in the bitstream configuration header, as will be discussed below) or implicitly (eg, by checking whether the SBR data is mono or stereo when PS encoding data is present).

As discussed above, a specialized element in the header of the bitstream transmitted from the encoder to the decoder can be used to signal the selected PS/SBR configuration. The specified bitstream header carries the necessary configuration information that is required to enable the decoder to correctly decode the data in the bitstream. The specialized element in the header of the bitstream may be, for example, a one-bit flag, field, or index pointing to a particular entry in a table that defines various decoder configurations.

Instead of including an additional specialized element in the header of the bitstream to signal the PS/SBR configuration, information that is already present in the bitstream can be evaluated by the decoding system to select the correct PS/SBR configuration. For example, the PS/SBR configuration selection may be inferred from the PS decoder and SBR decoder configuration information in the bitstream header. The configuration information generally indicates whether the SBR decoder should be configured for mono operations or stereo operations. If, for example, a PS decoder is enabled and the SBR decoder is configured for mono operations (as indicated in the configuration information), the PS/SBR configuration according to FIG. 14. If, for example, a PS decoder is enabled and the SBR decoder is configured for stereo operations (as indicated in the configuration information), the PS/SBR configuration according to FIG. 15.

The embodiments of the invention described above are merely illustrative of the principles of the present application. It should be understood that changes and modifications to the configurations and details described in this specification will be apparent to those skilled in the art. Therefore, it is intended that the scope of the claims of the application is not limited to the specific details presented by describing and explaining the embodiments of the invention in this specification.

The systems and methods disclosed in this application may be implemented as software, firmware, hardware, or a combination thereof. Some, or all, of the components may be implemented as software running on a digital signal processor or microprocessor, or implemented as hardware or ASICs.

Typical devices using the disclosed systems and methods are portable audio players, mobile communication devices, set-top boxes, televisions, AVRs (Audio Video Tuners), personal computers, and the like.

Claims (35)

1. An audio signal processing device for encoding a stereo signal into a bitstream signal, comprising one or more components that: generating an average stereo signal and SBR stereo parameters in response to the stereo signal; generating a downmix signal, a residual signal, and one or more parametric stereo coding parameters based on the average stereo signal, wherein the residual signal is indicative of an error associated with displaying the average signal by the downmix signal and one or more parametric stereo coding parameters; generating, in a frequency-dependent or frequency-independent manner, a first signal and a second signal based on: the sum of the downmix signal and the residual signal and the difference of the downmix signal and the residual signal, or the downmix signal and the residual signal; generating an encoded stereo signal by perceptually encoding the first signal and the second signal; And generating a bitstream signal by combining the SBR stereo parameters, the parametric stereo coding parameters, and the encoded stereo signal. 2. An audio signal processing device according to claim 1, characterized in that the perceptual encoding includes: generating, in a frequency-dependent or frequency-independent manner, an encoded stereo signal by performing: perceptual left/right coding of the first signal and the second signal; or perceptual middle/side coding of the first signal and the second signal. 3. An audio signal processing apparatus according to claim 2, wherein the perceptual encoding comprises selecting, in a frequency-dependent or frequency-independent manner, and based on the first signal and the second signal, between the perceptual left/right encoding of the first signal and the second signal and perceptual middle/side coding of the first signal and the second signal. 4. An audio signal processing device according to claim 2, characterized in that the perceptual left/right encoding of the first signal and the second signal is performed for some frequency bands, and the perceptual middle/side encoding of the first signal and the second signal is performed for other frequency bands. 5. An audio signal processing device for decoding a bitstream signal including SBR stereo parameters and one or more parametric stereo encoding parameters into a stereo signal containing one or more components that: generating a first signal and a second signal by perceptually decoding the bitstream signal; generating, in a frequency-dependent or frequency-independent manner, a downmix signal and a residual signal based on: the sum of the first signal and the second signal and the difference between the first signal and the second signal or the first signal and the second signal; generating an average stereo signal by performing an upmix operation in response to the downmix signal, the residual signal, and parametric stereo coding parameters, wherein the residual signal indicates an error associated with displaying the first signal and the second signal by the downmix signal and parametric stereo coding parameters; And generating a stereo signal by performing an SBR stereo decoding operation in response to the average stereo signal and the SBR stereo parameters. 6. An audio signal processing device according to claim 5, characterized in that the perceptual decoding of the bitstream signal includes: generating, in a frequency-dependent or frequency-independent manner, the first signal and the second signal by doing: perceptual left/right decoding of the bitstream signal; or perceptual middle/side decoding of the bitstream signal. 7. An audio signal processing apparatus according to claim 6, characterized in that perceptual left/right decoding of the bitstream signal is performed for some frequency bands, and perceptual middle/side decoding of the bitstream signal is performed for other frequency bands. 8. An audio signal processing device according to claim 5, characterized in that the parametric stereo encoding parameters include: a frequency-dependent or frequency-independent parameter indicative of the intensity difference between channels, and a frequency-dependent or frequency-independent parameter indicating cross-correlation between channels. 9. A method performed by an audio signal processor for decoding a bitstream signal including SBR stereo parameters and one or more parametric stereo coding parameters into a stereo signal, the method comprising: generating a first signal and a second signal by perceptually decoding the bitstream signal; generating, in a frequency-dependent or frequency-independent manner, the downmix signal and the residual signal based on: the sum of the first signal and the second signal, and based on the difference between the first signal and the second signal, or the first signal and the second signal; generating an average stereo signal by performing an upmix operation in response to the downmix signal, the residual signal, and parametric stereo coding parameters, wherein the residual signal indicates an error associated with displaying the first signal and the second signal by the downmix signal and parametric stereo coding parameters; and generating a stereo signal by performing an SBR stereo decoding operation in response to the average stereo signal and the SBR stereo parameters; wherein the method is performed at least in part by one or more components of the audio signal processing device. 10. A non-volatile computer-readable storage medium containing a sequence of commands, where, when executed by the audio signal processing device, the sequence of commands causes the audio signal processing device to carry out the method according to claim 9.

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