WO2010035972A2

WO2010035972A2 - An apparatus for processing an audio signal and method thereof

Info

Publication number: WO2010035972A2
Application number: PCT/KR2009/005189
Authority: WO
Inventors: Hyun Kook Lee; Sung Yong Yoon; Dong Soo Kim; Jae Hyun Lim
Original assignee: Lg Electronics Inc.
Priority date: 2008-09-25
Filing date: 2009-09-11
Publication date: 2010-04-01
Also published as: WO2010035972A3

Abstract

An apparatus for processing an audio signal and method thereof are disclosed, by which a band extension scheme can be selectively applied according to a characteristic of an audio signal. The present invention includes receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, by an audio processing apparatus, if the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme, and if the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

Description

[DESCRIPTION]

AN APPARATUS FOR PROCESSING AN AUDIO SIGNAL AND METHOD

THEREOF

TECHNICAL FIELD

The present invention relates to an apparatus for processing an audio signal and method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for encoding or decoding audio signals.

BACKGROUND ART

Generally, an audio signal has correlation between a low frequency band signal and a high frequency band signal within one frame. In consideration of the principle of the correlation, it is able to compress an audio signal by a band extension technology that encodes high frequency band spectral data using low frequency band spectral data.

DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM

However, in the related art, in case that low correlation exists between a low frequency band signal and a high frequency band signal, if an audio signal is compressed using a band extension scheme, a sound quality of the audio signal is degraded.

Specifically, in case of sibilant or the like, since the correlation is not high, the band extension scheme for the audio signal is not suitable for the sibilant or the like.

TECHNICAL SOLUTION Accordingly, the present invention is directed to an apparatus for processing an audio signal and method thereof that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an apparatus for processing an audio signal and method thereof, by which a band extension scheme can be selectively applied according to a characteristic of an audio signal.

Another object of the present invention is to provide an apparatus for processing an audio signal and method thereof, by which a suitable scheme can be adaptively applied according to a characteristic of an audio signal per frame instead of using a band extension scheme. A further object of the present invention is to provide an apparatus for processing an audio signal and method thereof, by which a quality of sound can be maintained by avoiding an application of a band extension scheme if an analyzed audio signal characteristic is close to sibilant.

ADVANTAGEOUS EFFECTS

Accordingly, the present invention provides the following effects and/or advantages.

First of all, the present invention selectively applies a band extension scheme per frame according to a characteristic of a signal per frame, thereby enhancing a quality of sound without incrementing the number of bits considerably.

Secondly, the present invention applies an LPC (linear predictive coding) scheme suitable for a speech signal, an HBE (high band extension) scheme or a scheme (PSDD) newly proposed by the present invention to a frame determined as including a sound (e.g., sibilant) having high frequency band energy therein instead of a band extension scheme, thereby minimizing a loss of sound quality. DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a block diagram of an audio signal processing apparatus according to an embodiment of the present invention; FIG. 2 is a detailed block diagram of a sibilant detecting unit shown in FIG. 1 ;

FIG. 3 is a diagram for explaining a principle of sibilant detecting; FIG. 4 is a diagram for an example of an energy spectrum for non-sibilant and an example of an energy spectrum for sibilant;

FIG. 5 is a diagram for examples of detailed configurations of a second encoding unit and a second decoding unit shown in FIG. 1 ;

FIG. 6 is a diagram for explaining first and second embodiments of a PSDD (partial spectral data duplication) scheme as an example of a non-band extension encoding/decoding scheme;

FIG. 7 and FIG. 8 are diagrams for explaining cases that a length of a frame differs in a PSDD scheme;

FIG. 9 is a block diagram for a first example of an audio signal encoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied;

FIG. 10 is a block diagram for a second example of an audio signal encoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied;

FIG. 11 is a block diagram for a first example of an audio signal decoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied; FIG. 12 is a block diagram for a second example of an audio signal decoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied;

FIG. 13 is a schematic diagram of a product in which an audio signal processing apparatus according to an embodiment of the present invention is implemented; and FIG. 14 is a diagram for relations of products provided with an audio signal processing apparatus according to an embodiment of the present invention.

BEST MODE

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for processing an audio signal according to the present invention includes receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, by an audio processing apparatus, when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme, and when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

Preferably, the higher band equal or higher than a boundary frequency is reconstructed using all or a portion of a narrow band which comprises continued bands equal or lower than the boundary frequency.

Preferably, the current frame is decoded using linear prediction coding scheme.

Preferably, the reconstructing the higher band includes receiving band extension information, wherein the higher band is reconstructed based on the band extension information. To further achieve these and other advantages and in accordance with the purpose of the present invention, an apparatus for processing an audio signal includes a demultiplexer receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, a first decoding part, when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme, and a second decoding part, when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

Preferably, the current frame is decoded using linear prediction coding scheme.

Preferably, the de-multiplexer receives band extension information and wherein the higher band is reconstructed based on the band extension information. To further achieve these and other advantages and in accordance with the purpose of the present invention, a method for processing an audio signal includes receiving a signal, by an audio processing apparatus, detecting a sibilant proportion of a current frame from the signal, generating coding scheme information indicating whether a band extension scheme is applied to the current frame, based on the sibilant proportion;, when the band extension scheme is applied to the current frame, generating band extension information using a narrow band of the current frame, and when the band extension scheme is not applied to the current frame, decoding a wide band of the current frame.

Preferably, the method further includes estimating energy per band from the signal and searching a peak band with maximum energy based on the energy per band, wherein the sibilant proportion is detected using the peak band and a threshold band.

To further achieve these and other advantages and in accordance with the purpose of the present invention, an apparatus for processing an audio signal includes a sibilant detecting part detecting a sibilant proportion of a current frame from a signal, the sibilant detecting part generating coding scheme information indicating whether a band extension scheme is applied to the current frame, based on the sibilant proportion, a first encoding part, when the band extension scheme is applied to the current frame, generating band extension information using a narrow band of the current frame, and a second encoding part, when the band extension scheme is not applied to the current frame, decoding a wide band of the current frame. Preferably, the apparatus further includes an energy estimating part estimating energy per band from the signal and a sibilant deciding part searching for a peak band with maximum energy based on the energy per band, wherein the sibilant proportion is detected using the peak band and a threshold band.

To further achieve these and other advantages and in accordance with the purpose of the present invention, a computer-readable medium includes instructions stored thereon, the instructions, if executed by a processor, enabling the processor to perform operations, the instructions including receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, by an audio processing apparatus, when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme, and when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. First of all, terminologies or words used in this specification and claims are not construed as limited to the general or dictionary meanings and should be construed as the meanings and concepts matching the technical idea of the present invention based on the principle that an inventor is able to appropriately define the concepts of the terminologies to describe the inventor's invention in best way. The embodiment disclosed in this disclosure and configurations shown in the accompanying drawings are just one preferred embodiment and do not represent all technical idea of the present invention. Therefore, it is understood that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents at the timing point of filing this application. The following terminologies in the present invention can be construed based on the following criteria and other terminologies failing to be explained can be construed according to the following purposes. First of all, it is understood that the concept 'coding' in the present invention can be construed as either encoding or decoding in case. Secondly, 'information' in this disclosure is the terminology that generally includes values, parameters, coefficients, elements and the like and its meaning can be construed as different occasionally, by which the present invention is non-limited.

In this disclosure, in a broad sense, an audio signal is conceptionally discriminated from a video signal and designates all kinds of signals that can be auditorily identified. In a narrow sense, the audio signal means a signal having none or small quantity of speech characteristics. Audio signal of the present invention should be construed in a broad sense. And, the audio signal of the present invention can be understood as a narrow-sense audio signal in case of being used by being discriminated from a speech signal. FIG. 1 is a block diagram of an audio signal processing apparatus according to an embodiment of the present invention.

Referring to FIG. 1, an encoder side 100 of an audio signal processing apparatus can include a sibilant detecting unit 110, a first encoding unit 122, a second encoding unit 124 and a multiplexing unit 130. A decoder side 200 of the audio signal processing apparatus can include a demultiplexer 210, a first decoding unit 222 and a second decoding unit 224.

The encoder side 100 of the audio signal processing apparatus determines whether to apply a band extension scheme according to a characteristic of an audio signal and then generates coding scheme information according to the determination. Subsequently, the decoder side 200 selects whether to apply the band extension scheme per frame according to the coding scheme information.

The sibilant detecting unit 110 detects a sibilant proportion for a current frame of an audio signal. Based on the detected sibilant proportion, the sibilant detecting unit 110 generates coding scheme information indicating whether the band extension scheme will be applied to the current frame. In this case, the sibilant proportion means an extent for a presence or non-presence of sibilant in the current frame. The sibilant is a consonant such as a hissing sound generated using friction of air sucked into a narrow gap between teeth. For instance, such a sibilant includes Α ', ' M ' and the like in Korean. For instance, such a sibilant includes such a consonant 's' in English. Meanwhile, affricate is a consonant sound that begins as a plosive and becomes a fricative such as ' ^ ', ' ^ ', '**', etc. in Korean. In this disclosure, 'sibilant' is not limited to a specific sound but indicates a sound of which peak band having maximum energy belonging to a frequency band higher than that of other sounds. Detailed configuration of the sibilant detecting unit 110 will be explained later with reference to FIG. 2. As a result of detecting the sibilant proportion, if it is determined that a prescribed frame has a less sibilant proportion, an audio signal is encoded by the first encoding unit 122. If it is determined that a prescribed frame has a more sibilant proportion, an audio signal is encoded by the second encoding unit 124.

The first encoding unit 122 is an element that encodes an audio signal in a frequency domain based band extension scheme. In this case, by the frequency domain based band extension scheme, spectral data corresponding to a higher band in wide band spectral data is encode using all or a portion of a narrow band. This scheme is able to reduce the bit number in consideration of the principle of correlation between a high frequency band and a low frequency band. In this case, the band extension scheme is based on a frequency domain and the spectral data is the data frequency-transformed by a QMF (quadrature mirror filter) filterbank or the like. A decoder reconstructs spectral data of a higher band from narrow band spectral data using band extension information. In this case, the higher band is a band having a frequency equal to or higher than a boundary frequency. The narrow band (or lower band) is a band having a frequency equal to or lower than a boundary frequency and is constructed with consecutive bands. This frequency domain based band extension scheme may conform with the SBR (spectral band replication) or eSBR (enhanced spectral band replication) standard, by which the present invention is non-limited.

Meanwhile, this frequency domain based band extension scheme is based on the correlation between a high frequency band and a low frequency band. And, this correlation may be strong or weak according to a characteristic of an audio signal. Specifically, in case of the above-mentioned sibilant, since the correlation is weak, if a band extension scheme is applied to a frame corresponding to the sibilant, a sound quality may be degraded. The application relation between energy characteristic of the sibilant and the frequency domain based band extension scheme will be explained in detail with reference to FIG. 3 and FIG. 4 later. The first encoding unit 122 may have the concept including an audio signal encoder explained in the following description with reference to FIG. 8, by which the present invention is non-limited.

The second encoding unit 124 is a unit that encodes an audio signal without using the frequency domain based band extension scheme. In this case, instead of not using band extension schemes of all types, the specific frequency domain based band extension scheme applied to the first encoding unit 122 is not used. First of all, the second encoding unit 124 corresponds to a speech signal encoder that applies a linear predictive coding (LPC) scheme. Secondly, the second encoding unit 124 further includes a module according to a time domain based band extension scheme as well as a speech encoder. Thirdly, the second encoding unit 124 is able to further include a module according to a PSDD (partial spectral data duplication) scheme newly proposed by this application. The corresponding details will be explained with reference to FIGs. 5 to 8 later. Meanwhile, the second time domain based band extension scheme may follow the HBE (high band extension) scheme applied to the AMR-WB (adaptive multi rate - wideband) standard, by which the present invention is non-limited.

The multiplexer 130 generates at least one bitstream by multiplexing the audio signal encoded by the first encoding unit 122 and the non-band extension encoding unit 124 with the coding scheme information generated by the sibilant detecting unit 110. The demultiplexer 210 of the decoder side extracts the coding scheme information from the bitstream and then delivers an audio signal of a current frame to the first decoding unit 222 or the second decoding unit 224 based on the coding scheme information. The first decoding unit 222 decodes the audio signal by the above-mentioned band extension scheme and the second decoding unit 224 decodes the audio signal by the above-mentioned LPC scheme (or HBE/PSDD scheme).

FIG. 2 is a detailed block diagram of the sibilant detecting unit shown in FIG. 1, FIG. 3 is a diagram for explaining a principle of sibilant detecting, and FIG. 4 is a diagram for an example of an energy spectrum for non-sibilant and an example of an energy spectrum for sibilant. Referring to FIG. 2, the sibilant detecting unit 110 includes a transforming part

112, an energy estimating part 114 and a sibilant decoding part 116.

The transforming part 112 transforms a time domain audio signal into a frequency domain signal by performing frequency transform on an audio signal. In this case, this frequency transform can use one of FFT (fast Fourier transform), MDCT (modified discrete cosine transform) and the like, by which the present invention is non-limited. The energy estimating part 114 calculates energy per band for a current frame by binding a frequency domain audio signal per several bands. The energy estimating part 114 then decides what is a peak band B_max having maximum energy in a whole band. The sibilant deciding part 116 detects a sibilant proportion of the current frame by deciding whether the band B_max having the maximum energy is higher or lower than a threshold band EW This is based on the characteristic that a vocal sound has maximum energy in a low frequency, whereas a sibilant has maximum energy in a high frequency. In this case, the threshold band Bu₁ may be a preset value set to a default value or a value calculated according to a characteristic of an inputted audio signal. Referring to FIG. 3, it can be observed that a wide band including a narrow band(or lower band) and a higher band exits. A peak band B_max having maximum energy E_max may be higher or lower than a threshold band B_th- Meanwhile, referring to FIG. 4, it can be observed that an energy peak of a signal of non-sibilant exits on a low frequency band. And, it can be also observed that an energy peak of a sibilant signal exists on a relatively high frequency band. Referring now to FIG. 3, In case of (A), since an energy peak exists in a relative low frequency, it is decided as non-sibilant. In case of (B), since an energy peak exists in a relative high frequency, it can be decided as sibilant.

Meanwhile, the formerly mentioned frequency domain based band extension scheme encodes a higher band higher than a boundary frequency using a narrow band lower than the boundary frequency. This scheme is based on the correlation between spectral data of narrow band and spectral data of higher band. Yet, in case of a signal of which energy peak exists in a high frequency, the correlation is relatively reduced. Thus, if the frequency domain based band extension scheme for predicting spectral data of higher band using spectral data of the narrow band is applied, it may degrade a quality of sound. Therefore, to a current frame decided as sibilant, it is preferable that another scheme is applied rather than the frequency domain based band extension scheme.

Referring now to FIG. 2, if a peak band B_max of an energy peak is lower than a threshold band B_th, the sibilant deciding part 116 decides a current frame as non-sibilant and then enables an audio signal to be encoded according to a frequency domain based band extension scheme by the first encoding unit. Otherwise, the sibilant deciding part 116 decides a current frame as sibilant and then enables an audio signal to be encoded according to an alternative scheme by the second encoding unit.

FIG. 5 is a diagram for examples of detailed configurations of the second encoding decoding units shown in FIG. 1. Referring to (A) of FIG. 5, a second encoding unit 124a according to a first embodiment includes an LPC encoding part 124a-l. And, a second decoding unit 224a according to the first embodiment includes an LPC decoding part 224a- 1. The LPC encoding part and the LPC decoding part are the elements for encoding or decoding an audio signal on a whole band by a linear prediction coding (LPC) scheme. The LPC (linear prediction coding) is to predict a current sample value in a manner of multiplying a predetermined number of previous sample values by a coefficient and then adding up the results. The LPC corresponds to a representative example of short term prediction (STP) for processing a speech signal on the basis of a time domain. If the LPC encoding part 124a-l generates an LPC coefficient (not shown in the drawing) encoded by the LPC scheme, the LPC decoding part 224a- 1 reconstructs an audio signal using the LPC coefficient.

Meanwhile, a second encoding unit 124b according to a second embodiment includes an HBE encoding part 124b-l and an LPC encoding part 124b-2. And, a second decoding unit 224b according to the second embodiment includes an LPC decoding part 224b- 1 and an HBE decoding part 224b-2. The HBE encoding part 124b-l and the HBE decoding part 224b-2 are elements for encoding/decoding an audio signal according to HBE scheme. The HBE (high band extension) scheme is a sort of a time domain based band extension scheme. An encoder generates HBE information, i.e., spectral envelope modeling information and frame energy information, for a high frequency signal and also generates an excitation signal for a low frequency signal. In this case, the spectral envelope modeling information may correspond to information indicating that an LP coefficient generated through time domain based LP (linear prediction) analysis is transformed into ISP (immittance spectral pair). The frame energy information may correspond to information determined by comparing original energy to synthesized energy per 64 subframes. A decoder generates a high frequency signal by shaping an excitation signal of a low frequency signal using the spectral envelope modeling information and the frame energy information. This HBE scheme differs from the above-mentioned frequency domain based band extension scheme in being based on a time domain. In aspect of time axis waveform, the sibilant is a very complicated and random noise-like signal. If the sibilant is band-extended based on a frequency domain, it may become very inaccurate. Yet, since the HBE is based on a time domain, it is able to appropriately process the sibilant. Meanwhile, if the HBE scheme further includes post-processing for reducing buzzness of a high frequency excitation signal, it is able to further enhance performance on a sibilant frame. Meanwhile, the LPC encoding part 124b-2 and the LPC decoding part 224b- 1 perform the same functions of the elements 124a-l and 224a- 1 having the same names of the first embodiments. According to the first embodiment, linear predictive encoding/decoding is performed on a whole band of a current frame. Yet, according to the second embodiment, linear predictive encoding is performed not on a whole band but on a narrow band (or lower band) after execution of HBE. After the linear predictive decoding has been performed on the narrow band, HBE decoding is performed.

A second encoding unit 124c according to a third embodiment includes a PSDD encoding part 124c-l and an LPC encoding part 124c-2. And, a second decoding unit 224c according to the third embodiment includes an LPC decoding part 224c- 1 and a PSDD decoding part 224c-2. The frequency domain based band extension scheme performed by the first encoding unit 122 shown in FIG. 1 uses all or a portion of a narrow band constructed with a low frequency band. On the contrary, PSDD (partial spectral data duplication) uses a copy band discretely distributed on a low frequency band and a high frequency band and then encodes a target band adjacent to the copy band. Corresponding details shall be explained with reference to FIGs. 6 to 8 later.

Meanwhile, the LPC encoding and decoding parts described with reference to (A) to (C) of FIG. 5 can belong to speech signal encoder and decoder 440 and 630, which will be described with reference to FIGs. 9 to 12, respectively.

FIG. 6 is a diagram for explaining first and second embodiments of a PSDD (partial spectral data duplication) scheme as an example of a non-band extension encoding/decoding scheme.

Referring to (A) of FIG. 6, there exist total n scale factor bands sfb₀ to sfb_n-1 ranging from a low frequency to a high frequency, i.e., 0^th to (n-l)*. And, spectral data corresponding to the scale factor bands sfb₀ to sfb_n-1 exist, respectively. Spectral data sdj belonging to a specific band may mean a set of a plurality of spectral data sd; o to sdi__m-1. And, it is able to generate the number m; of spectral data to correspond to a spectral data unit, a band unit or a higher unit.

In this case, a band for transferring data to a decoder includes a low frequency band (sfbo, ..., sfb_s-i) and a copy band (cb) (sfb_s, sfb_n-4, sfb_n-2) in a whole band (sfb₀, ..., sfbn-i). The copy band is a band starting from a start band (sb) or a start frequency and is used for prediction of a target band (tb) (sfb_s+i, sfb_n-3, sfb_n-1). The target band is a band predicted using the copy band and does not transfer spectral data to a decoder.

Referring to (A) of FIG. 6, since the copy band exists on a high frequency band instead of being concentrated on a low frequency band. Since the copy band is adjacent to the target band, it is able to maintain correlation with the target band. Meanwhile, it is able to generate gain information (g) that is a difference between spectral data of a copy band and spectral data of a target band. Even if a target bad is predicted using a copy band, it is able to minimize degradation of a sound quality without increasing a bit rate less than that of a band extension scheme. In (A) of FIG. 6, shown is an example that a bandwidth of a cop band is equal to a bandwidth o a target band. In (B) of FIG. 6, shown is an example that a bandwidth of a cop band is different from a bandwidth o a target band.

Referring to (B) of FIG. 6, a bandwidth of a target band is at least two times (tb, tb') greater than a bandwidth of a copy band. In this case, it is able to apply different gains (g_s, g_s+1) to a left band tb and a right band tb' among the consecutive bands constructing the target band, respectively.

FIG. 7 and FIG. 8 are diagrams for explaining cases that a length of a frame differs in a PSDD scheme. FIG. 7 shows a case that the number N_t of spectral data of a target band is greater than the number N_c of spectral data of a copy band. FIG. 8 shows a case that the number N_t of spectral data of a target band is smaller than the number N_c of spectral data of a copy band.

Referring to (A) of FIG. 7, it can be observed that the number N_t of spectral data of a target band sfb, is 36 and the number N_c of spectral data of a copy band sfb_s is 24. As the number of data gets incremented, a horizontal length of a band is represented longer. Since the data number of the target band is greater, it is able to use data of the copy band at least twice. For instance, referring to (Bl) of FIG. 7, 24 data of a copy band is preferentially padded into a low frequency of a target band. Referring to (B2) of FIG. 7, it is able to front or rear 12 data of the copy band can be padded into the rest part of the target band. Of course, it is able to apply the transferred gain information as well. Referring to (A) of FIG. 8, it can be observed that the number N_t of spectral data of a target band sfb; is 24 and the number N₀ of spectral data of a copy band sfb_s is 36. Since the data number of the target band is smaller, it is just able to partially use data of the copy band. For instance, referring to (B) of FIG. 8, it is able to generate spectral data of the target band sfbi using 24 spectral data in a front part of the copy band sfb_s only. Referring to (C) of FIG. 8, it is able to generate spectral data of the target band sfbi using 24 spectral data in a rear part of the copy band sfb_s only.

FIG. 9 shows a first example of an audio signal encoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied. And, FIG. 10 shows a second example of the audio signal encoding device. The first example is an encoding device to which the first embodiment 124a of the second encoding unit described with reference to (A) of FIG. 5 is applied. The second example is an encoding device to which the second/third embodiment 124b/ 124c of the second encoding unit described with reference to (B)/(C) of FIG. 5 is applied.

Referring to FIG. 9, an audio signal encoding device 300 includes a plural-channel encoder 305, a sibilant detecting unit 310, a first encoding unit 322, an audio signal encoder 330, a speech signal encoder 340 and a multiplexer 350. In this case, the sibilant detecting unit 310 and the first encoding unit 320 can have the same functions of the former elements 110 and 122 having the same names described with reference to FIG 1.

The plural-channel encoder 305 generates a mono or stereo downmix signal by receiving an input of a plurality of channel signals (at least two channel signals) (hereinafter named a multi-channel signal) and then performing downmixing thereon. And, the plural-channel encoder 305 generates spatial information necessary to upmix a downmix signal into a multi-channel signal. In this case, the spatial information can include channel level difference information, inter-channel correlation information, channel prediction coefficient, downmix gain information and the like. If the audio signal encoding device 300 receives a mono signal, it is understood that the mono signal can bypass the plural-channel encoder 305 without being downmixed.

The sibilant detecting unit 310 detects a sibilant proportion of a current frame. If the detected sibilant proportion is non-sibilant, the sibilant detecting unit 310 delivers an audio signal to the first encoding unit 322. If the detected sibilant proportion is sibilant, an audio signal bypasses the first encoding unit 322 and the sibilant detecting unit 310 delivers the audio signal to the speech signal encoder 340. The sibilant detecting unit 310 generates coding scheme information indicating whether a band extension coding scheme is applied to the current frame and then delivers the generated coding scheme information to the multiplexer 350.

The first encoding unit 322 generates spectral data of narrow band and band extension information by applying the frequency domain based band extension scheme, which was described with reference to FIG. 1 , to an audio signal of a wide band.

If a specific frame or segment of a downmix signal has a large audio characteristic, the audio signal encoder 330 encodes the downmix signal according to an audio coding scheme. In this case, the audio coding scheme may follow the AAC (advanced audio coding) standard or the HE-AAC (high efficiency advanced audio coding) standard, by which the present invention is non-limited. Meanwhile, the audio signal encoder 340 may correspond to an MDCT (modified discrete transform) encoder. If a specific frame or segment of a downmix signal has a large speech characteristic, the speech signal encoder 340 encodes the downmix signal according to a speech coding scheme. In this case, the speech coding scheme may follow the AMR-WB (adaptive multi-rate wide-band) standard, by which the present invention is non-limited. Meanwhile, the speech signal encoder 340 can further include the former LPC (linear prediction coding) encoding part 124a-l, 124b-l or 124c-l described with reference to FIG. 5. If a harmonic signal has high redundancy on a time axis, it can be modeled by linear prediction for predicting a present signal from a past signal. In this case, if a linear prediction coding scheme is adopted, it is able to raise coding efficiency. Meanwhile, the speech signal encoder 340 can correspond to a time domain encoder. And, the multiplexer 350 generates an audio signal bitstream by multiplexing spatial information, coding scheme information, band extension information, spectral data and the like.

As mentioned in the foregoing description, FIG. 10 shows the example of an encoding device to which the second/third embodiment 124b/ 124c of the second encoding unit described with reference to (B)/(C) of FIG. 5 is applied. This example is almost the same of the first example described with reference to FIG. 9. This example differs from the first example in that an audio signal corresponding to a whole band is encoded by an HBE encoding part 424 (or a PSDD encoding part) according to an HBE scheme or a PSDD scheme prior to being encoded by a speech signal encoder 440. As mentioned in the foregoing description with reference to FIG. 5, the HBE encoding part 424 generates HBE information by encoding an audio signal according to the time domain based band extension scheme. The HBE encoding part 424 can be replaced by the PSDD encoding part 424. As mentioned in the foregoing description with reference to FIGs. 6 to 8, the PSDD encoding part 424 encodes a target band using information of the copy band and then generates PSDD information for reconstructing the target band. The speech signal encoder 440 encodes the result, which was encoded according to the HBE or PSDD scheme, according to a speech signal scheme. Of course, the speech signal encoder 440 can further include an LPC encoding part like the first example.

FIG. 11 shows a first example of an audio signal decoding device to which an audio signal processing apparatus according to an embodiment of the present invention is applied, and FIG 12 shows a second example of the audio signal decoding device. The first example is a decoding device to which the first embodiment 224a of the second decoding unit described with reference to (A) of FIG. 5 is applied. The second example is a decoding device to which the second/third embodiment 224b/224c of the second decoding unit described with reference to (B)/(C) of FIG. 5 is applied.

Referring to FIG. 11, an audio signal decoding device 500 includes a demultiplexer 510, an audio signal decoder 520, a speech signal decoder 530, a first decoding unit 540 and a plural-channel decoder 550.

The demultiplexer 510 extracts spectral data, coding scheme information, band extension information, spatial information and the like from an audio signal bitstream. The demultiplexer 510 delivers an audio signal corresponding to a current frame to the audio signal decoder 520 or the speech signal decoder 530 according to the coding scheme information. In particular, in case that the coding scheme information indicates that a band extension scheme is applied to the current frame, the demultiplexer 510 delivers the audio signal to the audio signal decoder 520. In case that the coding scheme information indicates that a band extension scheme is not applied to the current frame, the demultiplexer 510 delivers the audio signal to the speech signal decoder 530.

If spectral data corresponding to a downmix signal has a large audio characteristic, the audio signal decoder 520 decodes the spectral data according to an audio coding scheme. In this case, as mentioned in the foregoing description, the audio coding scheme can follow the AAC standard or the HE-AAC standard. Meanwhile, the audio signal decoder 520 can include a dequantizing unit (not shown in the drawing) and an inverse transform unit (not shown in the drawing). Therefore, the audio signal decoder 520 is able to perform dequantization and inverse transform on spectral data and scale factor carried on a bitstream.

If the spectral data has a large speech characteristic, the speech signal decoder 530 decodes a downmix signal according to a speech coding scheme. As mentioned in the forgoing description, the speech coding scheme may follow the AMR-WB (adaptive multi-rate wide-band) standard, by which the present invention is non-limited. As mentioned in the foregoing description with reference to FIG. 5, the speech signal decoder 530 can include the LPC decoding part 224a- 1, 224b- 1 or 224c- 1.

The first decoding unit 540 decodes a band extension information bitstream and then generates an audio signal of a high frequency band by applying the aforesaid frequency domain based band extension scheme to an audio signal using the decoded information.

If the decoded audio signal is a downmix, the plural-channel decoder 550 generates an output channel signal of a multi-channel signal (stereo signal included) using spatial information.

As mentioned in the foregoing description, FIG. 12 shows the example of a decoding device to which the second/third embodiment 224b/224c of the second decoding unit described with reference to (B)/(C) of FIG. 5 is applied. This example is almost the same of the first example described with reference to FIG 11. This example differs from the first example in that an audio signal corresponding to a whole band is decoded by an HBE decoding part 635 (or a PSDD decoding part) according to an HBE scheme or a PSDD scheme after having been decoded by a speech signal decoder 630. As mentioned in the foregoing description, the HBE decoding part 635 generates a high frequency signal by shaping an excitation signal of a low frequency using the HBE information. Meanwhile, the PSDD decoding part 635 reconstructs a target band using information of a copy band and PSDD information. The speech signal decoder 635 decodes the result, which was decoded according to the HBE or PSDD scheme, according to a speech signal scheme. Of course, the speech signal decoder 635 can further include an LPC decoding part 224a- 1, 224b- 1 or 224c- 1 like the first example.

The audio signal processing apparatus according to the present invention is available for various products to use. Theses products can be grouped into a stand alone group and a portable group. A TV, a monitor, a settop box and the like can be included in the stand alone group. And, a PMP, a mobile phone, a navigation system and the like can be included in the portable group.

FIG. 13 is a schematic diagram of a product in which an audio signal processing apparatus according to an embodiment of the present invention is implemented. Referring to FIG. 13, a wire/wireless communication unit 710 receives a bitstream via wire/wireless communication system. In particular, the wire/wireless communication unit 710 can include at least one of a wire communication unit 710A, an infrared unit 710B, a Bluetooth unit 710C and a wireless LAN unit 710D.

A user authenticating unit 720 receives an input of user information and then performs user authentication. The user authenticating unit 720 can include at least one of a fingerprint recognizing unit 720A, an iris recognizing unit 720B, a face recognizing unit 720C and a voice recognizing unit 720D. The fingerprint recognizing unit 720A, the iris recognizing unit 720B, the face recognizing unit 720C and the speech recognizing unit 720D receive fingerprint information, iris information, face contour information and voice information and then convert them into user informations, respectively. Whether each of the user informations matches pre-registered user data is determined to perform the user authentication.

An input unit 730 is an input device enabling a user to input various kinds of commands and can include at least one of a keypad unit 730A, a touchpad unit 730B and a remote controller unit 730C, by which the present invention is non-limited.

A signal coding unit 740 performs encoding or decoding on an audio signal and/or a video signal, which is received via the wire/wireless communication unit 710, and then outputs an audio signal in time domain. The signal coding unit 740 includes an audio signal processing apparatus 745. As mentioned in the foregoing description, the audio signal processing apparatus 745 corresponds to the above-described embodiment of the present invention. Thus, the audio signal processing apparatus 745 and the signal coding unit including the same can be implemented by at least one or more processors.

A control unit 750 receives input signals from input devices and controls all processes of the signal decoding unit 740 and an output unit 760. In particular, the output unit 760 is an element configured to output an output signal generated by the signal decoding unit 740 and the like and can include a speaker unit 760A and a display unit 760B. If the output signal is an audio signal, it is outputted to a speaker. If the output signal is a video signal, it is outputted via a display.

FIG. 14 is a diagram for relations of products provided with an audio signal processing apparatus according to an embodiment of the present invention. FIG. 14 shows the relation between a terminal and server corresponding to the products shown in FIG. 13.

Referring to (A) of FIG 14, it can be observed that a first terminal 700.1 and a second terminal 700.2 can exchange data or bitstreams bi-directionally with each other via the wire/wireless communication units. Referring to FIG. (B) of FIG. 14, it can be observed that a server 800 and a first terminal 700.1 can perform wire/wireless communication with each other.

An audio signal processing method according to the present invention can be implemented into a computer-executable program and can be stored in a computer- readable recording medium. And, multimedia data having a data structure of the present invention can be stored in the computer-readable recording medium. The computer- readable media include all kinds of recording devices in which data readable by a computer system are stored. The computer-readable media include ROM, RAM, CD- ROM, magnetic tapes, floppy discs, optical data storage devices, and the like for example and also include carrier-wave type implementations (e.g., transmission via Internet). And, a bitstream generated by the above encoding method can be stored in the computer- readable recording medium or can be transmitted via wire/wireless communication network.

INDUSTRIAL APPLICABILITY Accordingly, the present invention is applicable to processing and outputting an audio signal.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.

Claims

[CLAIMS!

L A method for processing an audio signal, comprising: receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, by an audio processing apparatus; when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme; and, when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

2. The method of claim 1, wherein the higher band equal or higher than a boundary frequency is reconstructed using all or a portion of a lower band which comprises continued bands equal or lower than the boundary frequency.

3. The method of claim 1, wherein the current frame is decoded using linear prediction coding scheme.

4. The method of claim 1, wherein the reconstructing the higher band comprises: receiving a band extension information, wherein the higher band is reconstructed based on the band extension information.

5. An apparatus for processing an audio signal, comprising: a de-multiplexer receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal; a first decoding part, when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme; and a second decoding part, when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.

6. The apparatus of claim 5, wherein the higher band equal or higher than a boundary frequency is reconstructed using all or a portion of a lower band which comprises continued bands equal or lower than the boundary frequency.

7. The apparatus of claim 5, wherein the current frame is decoded using linear prediction coding scheme.

8. The apparatus of claim 5, wherein the de-multiplexer receives band extension information and wherein the higher band is reconstructed based on the band extension information.

9. A method for processing an audio signal, comprising: receiving a signal, by an audio processing apparatus; detecting a sibilant proportion of a current frame from the signal; generating coding scheme information indicating whether a band extension scheme is applied to the current frame, based on the sibilant proportion; when the band extension scheme is applied to the current frame, generating band extension information using a narrow band of the current frame; and when the band extension scheme is not applied to the current frame, decoding a wide band of the current frame.

10. The method of claim 9, further comprising: estimating energy per band from the signal; and searching a peak band with maximum energy based on the energy per band, wherein the sibilant proportion is detected using the peak band and a threshold band.

11. An apparatus for processing an audio signal, comprising: a sibilant detecting part detecting a sibilant proportion of a current frame from a signal, the sibilant detecting part generating coding scheme information indicating whether a band extension scheme is applied to the current frame, based on the sibilant proportion; a first encoding part, when the band extension scheme is applied to the current frame, generating band extension information using a narrow band of the current frame; and a second encoding part, when the band extension scheme is not applied to the current frame, decoding a wide band of the current frame.

12. The apparatus of claim 11, further comprising: an energy estimating part estimating energy per band from the signal; and a sibilant deciding part searching for a peak band with maximum energy based on the energy per band, wherein the sibilant proportion is detected using the peak band and a threshold band.

13. A computer-readable medium comprising instructions stored thereon, the instructions, if executed by a processor, enabling the processor to perform operations, the instructions comprising: receiving a signal and coding scheme information indicating whether a band extension scheme is applied to a current frame of the signal, by an audio processing apparatus; when the coding scheme information indicates that the band extension scheme is applied to the current frame, reconstructing a higher band in the current frame using the band extension scheme; and when the coding scheme information indicates that the band extension scheme is not applied to the current frame, decoding the current frame without using the band extension scheme.