KR20150103643A - Method and apparatus for decoding high frequency for bandwidth extension - Google Patents

Abstract

Disclosed are a method and an apparatus for decoding high frequency for bandwidth expansion. A method for decoding high frequency for bandwidth expansion comprises the steps of; decoding an excitation class; transforming a decoded low frequency spectrum based on the excitation class; and generating high frequency excitation spectrum based on the transformed low frequency spectrum.

Description

METHOD AND APPARATUS FOR DECODING HIGH FREQUENCY FOR BANDWIDTH EXTENSION BACKGROUND OF THE INVENTION [0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to audio encoding and decoding, and more particularly, to a high-frequency decoding method and apparatus for bandwidth extension.

The coding scheme of G.719 is developed and standardized for the purpose of teleconferencing. It performs frequency domain conversion by performing MDCT (Modified Discrete Cosine Transform), and directly encodes the MDCT spectrum in the case of a stationary frame do. Non-stationary frames change their time domain aliasing order to change their temporal characteristics. The spectrum obtained for the non-stationary frame can be configured in a similar form to the stationary frame by performing interleaving to construct the codec with the same framework as the stationary frame. The energy of the thus configured spectrum is obtained, and the quantization is performed after performing the normalization. The normalized energy is represented by the RMS value. The normalized spectrum generates necessary bits for each band through energy-based bit allocation, and generates a bitstream through quantization and lossless coding based on the bit allocation information for each band.

According to the decoding scheme of G.719, inverse quantization of energy in the bitstream is performed in the inverse process of the coding scheme, inverse quantization of spectrum is performed by generating bit allocation information based on the dequantized energy, and a normalized dequantized spectrum . At this time, if there is a shortage of bits, a specific band may not have a dequantized spectrum. In order to generate noise for this specific band, a noise filling method is applied in which a noise codebook is generated based on an inversely quantized spectrum of a low frequency band and noise is generated according to a transmitted noise level. On the other hand, a bandwidth extension technique for folding low-frequency signals and generating high-frequency signals is applied to bands over a specific frequency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-frequency decoding method and apparatus for expanding a bandwidth capable of improving restored sound quality and a multimedia device employing the same.

According to another aspect of the present invention, there is provided a high frequency decoding method for bandwidth extension, comprising: decoding an excitation class; Modifying the decoded low frequency spectrum based on the excitation class; And generating a high frequency excitation spectrum based on the modified low frequency spectrum.

According to an aspect of the present invention, there is provided a high frequency decoding apparatus for bandwidth extension, the apparatus comprising: an excitation class decoding unit for decoding an excitation class, modifying the decoded low frequency spectrum based on the excitation class, And at least one processor for generating an excitation spectrum.

According to the high-frequency decoding method and apparatus for bandwidth extension according to the embodiments, high-frequency excitation spectra are generated by modifying the decoded low-frequency spectrum, so that the reconstructed sound quality can be improved without increasing the complexity excessively.

1 is a view for explaining an example of a subband configuration of a low frequency band and a high frequency band according to an embodiment
FIGS. 2A to 2C are diagrams for dividing the R0 band and the R1 band into R2, R3, R4, and R5 according to a selected coding scheme according to an exemplary embodiment.
3 is a view for explaining an example of a subband configuration in a high frequency band according to an embodiment.
4 is a block diagram illustrating a configuration of an audio encoding apparatus according to an embodiment.
5 is a block diagram illustrating a configuration of a BWE parameter generation unit according to an embodiment.
6 is a block diagram illustrating a configuration of an audio decoding apparatus according to an embodiment of the present invention.
7 is a block diagram showing a configuration of a high-frequency decoding apparatus according to an embodiment.
8 is a block diagram illustrating the configuration of a low-frequency spectrum transform unit according to an embodiment.
9 is a block diagram showing the configuration of a low-frequency spectrum transform unit according to another embodiment.
10 is a block diagram showing the configuration of a low-frequency spectrum transform unit according to another embodiment.
11 is a block diagram showing the configuration of a low-frequency spectrum transform unit according to another embodiment.
12 is a block diagram showing a configuration of a dynamic range control unit according to an embodiment.
13 is a block diagram showing a configuration of a high frequency excitation spectrum generation unit according to an embodiment.
FIG. 14 is a diagram for explaining smoothing processing on a weight at a band boundary; FIG.
FIG. 15 is a view for explaining a weight, which is a contribution used for reconstructing a spectrum existing in an overlapping region according to an embodiment.
16 is a block diagram illustrating a configuration of a multimedia device including a decoding module according to an embodiment.
17 is a block diagram illustrating a multimedia device including a coding module and a decoding module according to an embodiment.
18 is a flowchart for explaining the operation of the high-frequency decoding method according to an embodiment.
19 is a flowchart for explaining the operation of the low frequency spectrum transform method according to an embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and are specifically described in the detailed description. It should be understood, however, that the present invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components are not limited by terms. Terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, the term "comprises" or "having ", etc. is intended to specify that there is a feature, number, step, operation, element, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Referring to the accompanying drawings, the same or corresponding components are denoted by the same reference numerals, do.

1 is a view for explaining an example of a subband configuration of a low frequency band and a high frequency band according to an embodiment. According to the embodiment, the sampling rate is 32 kHz, and the 640 MDCT spectrum coefficients are composed of 22 bands. Specifically, the MDCT spectrum coefficient is composed of 17 bands for the low frequency band and 5 bands for the high frequency band. For example, the starting frequency of the high frequency band is the 241st spectral coefficient, and the spectral coefficient from 0 to 240 is the low frequency coding method, that is, the area coded by the core coding method, and can be defined as R0. In addition, the spectral coefficients from 241 to 639 can be defined as R1 as a high frequency band in which bandwidth extension (BWE) is performed. On the other hand, a band coded by a low-frequency coding scheme may exist in the R1 region according to the bit allocation information.

FIGS. 2A to 2C are diagrams for dividing the R0 region and the R1 region of FIG. 1 into R2, R3, R4, and R5 according to a selected coding scheme. First, the BWE region R1 region can be divided into R2 and R3, and the low frequency coding region R0 region can be divided into R4 and R5 regions. R2 denotes a band including a signal subjected to quantization and lossless coding in a low-frequency coding scheme, for example, a frequency domain coding scheme, and R3 denotes a band having no signal coded in a low-frequency coding scheme. On the other hand, even if it is determined that R2 is allocated and coded in the low-frequency coding scheme, bands can be generated in the same manner as in R3 if the bits are insufficient. R5 denotes a band to which a bit is assigned and coding is performed by a low-frequency coding scheme, and R4 denotes a band to which noise is added because coding is not performed or bits are allocated even though the signal is a low frequency signal because there is no bit redundancy. Therefore, the distinction between R4 and R5 can be determined by the addition of noise, which can be determined by the ratio of the number of spectrums in the low-frequency coded band, or in the case of using FPC, based on the in-band pulse allocation information . Since the R4 and R5 bands can be distinguished when adding noise in the decoding process, they may not be clearly distinguished in the encoding process. The R2 to R5 bands are not only different in information to be encoded, but can be applied to different decoding schemes.

In the example shown in FIG. 2A, the two bands from 170 to 240 of the low-frequency coding region R0 are R4 to which noise is added, and the two bands from 241 to 350 in the BWE region R1, And the two bands are R2 encoded in a low-frequency coding scheme. In the example shown in FIG. 2B, one band from 202 to 240 of the low-frequency coding region R0 is R4 to which noise is added, and all five bands from 241 to 639 in the BWE region R1 are low- Lt; / RTI > In the example shown in Fig. 2C, the three bands from 144 to 240 among the low-frequency coding areas R0 are R4 to which noise is added, and R2 in the BWE area R1 does not exist. In the low-frequency coding region R0, R4 may be normally distributed in the high-frequency portion, but R2 in the BWE region R1 is not limited to a specific frequency portion.

FIG. 3 is a view for explaining an example of a subband configuration of a high frequency band of a wide band (WB) according to an embodiment. Here, the 32 KHz sampling rate is 32 kHz, and 640 MDCT spectral coefficients can be composed of 14 bands for the medium-to-high frequency band. 100 Hz includes four spectral coefficients, so the first band of 400 Hz can include 16 spectral coefficients. Reference numeral 310 denotes a high frequency band of 6.4 to 14.4 KHz, and reference numeral 330 denotes a sub band configuration of a high frequency band of 8.0 to 16.0 KHz.

4 is a block diagram illustrating a configuration of an audio encoding apparatus according to an embodiment.

4 may include a BWE parameter generation unit 410, a low-frequency encoding unit 430, a high-frequency encoding unit 450, and a multiplexing unit 470. Each component may be integrated with at least one module and implemented with at least one processor (not shown). Here, the input signal may be a music signal, a voice signal, or a mixed signal of music and voice, and may be divided into a general signal different from a voice signal. Hereinafter, they will be collectively referred to as audio signals for convenience of explanation.

Referring to FIG. 4, the BWE parameter generator 410 may generate a BWE parameter for bandwidth extension. Here, the BWE parameter may correspond to an excitation class. On the other hand, depending on the implementation, the BWE parameter may include parameters different from the excitation class. The BWE parameter generation unit 410 can generate an excitation class based on the signal characteristics on a frame-by-frame basis. Specifically, it can be determined whether the input signal has a voice characteristic or a tonal characteristic, and one of a plurality of excitation classes can be determined based on the determination result. The plurality of excitation classes may include excitation classes associated with speech, excitation classes associated with tonal music, and excitation classes associated with non-tonal music. The determined excitation class can be included in the bitstream and transmitted.

The low-frequency encoding unit 430 may encode a low-band signal to generate an encoded spectral coefficient. In addition, the low-frequency encoding unit 430 can encode information related to the energy of the low-band signal. According to the embodiment, the low-frequency encoding unit 430 may convert a low-band signal into a frequency domain to generate a low-frequency spectrum, and quantize the low-frequency spectrum to generate a quantized spectral coefficient. Modified Discrete Cosine Transform (MDCT) may be used for domain conversion, but the present invention is not limited thereto. For quantization, PVQ (Pyramid Vector Quantization) may be used but is not limited thereto.

The high-frequency encoding unit 450 may encode a high-band signal to generate a parameter necessary for bandwidth extension at a decoder end or a parameter necessary for bit allocation. The parameters needed for bandwidth extension may include information related to the energy of the highband signal and additional information. Here, the energy can be expressed by an envelope, a scale factor, an average power or Norm. The additional information may be information on bands including important frequency components in a high band, and information related to frequency components included in a specific high frequency band. The high-frequency encoding unit 450 converts a high-band signal into a frequency domain to generate a high-frequency spectrum, and quantizes information related to energy of the high-frequency spectrum. MDCT can be used for domain conversion but is not limited thereto. Vector quantization may be used for quantization, but is not limited thereto.

The multiplexer 470 may generate a bitstream including a BWE parameter, i.e., an excitation class, a parameter required for bandwidth extension, a parameter required for bit allocation, and a low-band encoded spectral coefficient. The bitstream may be transmitted or stored.

The BWE scheme of the frequency domain can be applied in combination with the time domain coding part. The CELP scheme can be mainly used for the time domain coding, and the low frequency band can be coded by the CELP scheme and combined with the BWE scheme in the time domain instead of the BWE in the frequency domain. In this case, the coding scheme can be selectively applied based on the determination of the adaptive coding scheme between the time domain coding and the frequency domain coding as a whole. In order to select an appropriate coding scheme, a signal classification is required. According to an exemplary embodiment, the signal classification result may be preferentially used to determine an excitation class for each frame.

FIG. 5 is a block diagram illustrating a configuration of a BWE parameter generator 410 (FIG. 4) according to an exemplary embodiment, and may include a signal classifier 510 and an excursion class generator 530.

Referring to FIG. 5, the signal classifier 510 classifies whether the current frame is a speech signal by analyzing the signal characteristics on a frame-by-frame basis, and determines an excursion class according to the classification result. The signal classification processing can be performed using various known methods, for example, short-term characteristic and / or long-term characteristic. The short term characteristic and / or the long term characteristic may be a frequency domain characteristic or a time domain characteristic. In the case where the current frame is classified into a voice signal in which the time domain coding is an appropriate method, a method of allocating a fixed type excitation class rather than a method based on characteristics of a high-band signal may be helpful for improving sound quality. Here, the signal classification processing can be performed on the current frame without considering the classification result of the previous frame. That is, although the current frame may be finally determined as frequency domain coding considering the hangover, a fixed excursion class may be allocated when the current frame itself is classified as a proper time domain coding. For example, if the current frame is classified as a speech signal for which time domain coding is appropriate, the excitation class may be set to a first excitation class associated with the speech characteristic.

If the current frame is not classified as a speech signal as a result of classification by the signal classifying unit 510, the class generating unit 530 may determine the excitation class using at least one threshold value. According to the embodiment, when the current frame is not classified as a speech signal as a result of classification by the signal classifying unit 510, the excursion class generating unit 530 calculates a high-bandwidth threshold value and outputs the threshold value as a threshold The class can be determined. A plurality of threshold values may be used depending on the number of classes. When one threshold value is used, it can be classified into a tonal music signal when the tonality value is larger than the threshold value and a non-tonal music signal, for example, a noisy signal when the tonality value is smaller than the threshold value. If the current frame is classified as a tonal music signal, the excitation class may be determined to be a second excitation class related to the tonal characteristics, or a third excitation class related to the non-tonal characteristics if it is classified as the noisy signal.

6 is a block diagram illustrating a configuration of an audio decoding apparatus according to an embodiment of the present invention.

6 may include a demultiplexing unit 610, a BWE parameter decoding unit 630, a low-frequency decoding unit 650, and a high-frequency decoding unit 670. Although not shown, the audio decoding apparatus may further include a spectrum combining unit and an inverse transforming unit. Each component may be integrated with at least one module and implemented with at least one processor (not shown). Here, the input signal may be a music signal, a voice signal, or a mixed signal of music and voice, and may be divided into a general signal different from a voice signal. Hereinafter, they will be collectively referred to as audio signals for convenience of explanation.

Referring to FIG. 6, the demultiplexer 610 may parse a received bitstream to generate parameters necessary for decoding.

The BWE parameter decoding unit 630 can decode the BWE parameter from the bitstream. The BWE parameter may correspond to the class here. On the other hand, the BWE parameter may include parameters different from the excitation class.

The low-frequency decoding unit 650 can generate a low-frequency spectrum by decoding low-band encoded spectral coefficients from the bitstream. Meanwhile, the low-frequency decoding unit 650 can decode information related to the energy of the low-band signal.

The high-frequency decoding unit 670 can generate a high-frequency excitation spectrum using the decoded low-frequency spectrum and the excitation class. According to another embodiment, the high-frequency decoding unit 670 decodes parameters necessary for bandwidth extension or parameters required for bit allocation from the bitstream, and generates parameters necessary for bandwidth extension or parameters required for bit allocation and energy of decoded low- Can be applied to the high frequency excitation spectrum.

The parameters needed for bandwidth extension may include information related to the energy of the highband signal and additional information. The additional information may be information on bands including important frequency components in a high band, and information related to frequency components included in a specific high frequency band. Information related to the energy of the highband signal can be vector dequantized.

The spectrum combining unit (not shown) may combine the spectrum provided from the low-frequency decoding unit 650 with the spectrum provided from the high-frequency decoding unit 670. The inverse transformer (not shown) can invert the combined spectrum into the time domain. IMDCT (Inverse MDCT) may be used for inverse domain conversion, but is not limited thereto.

FIG. 7 is a block diagram illustrating a configuration of a high-frequency decoding apparatus according to an embodiment, and may be implemented by a high-frequency decoding unit 670 of FIG. 6 or a separate apparatus. The high-frequency decoding apparatus of FIG. 7 may include a low-frequency spectrum deformation unit 710 and a high-frequency excitation spectrum generation unit 730. Although not shown here, it may further include a receiver for receiving the decoded low-frequency spectrum.

Referring to FIG. 7, the low-frequency spectrum transformer 710 may modify the decoded low-frequency spectrum based on the excitation class. According to one embodiment, the decoded low frequency spectrum may be a noise-filled processed spectrum. According to another embodiment, the decoded low-frequency spectrum may be an anti-sparseness spectrum that inserts a random code and a coefficient with a certain amplitude again at the remaining portion after noise- have.

The high frequency excitation spectrum generation unit 730 can generate a high frequency excitation spectrum from the modified low frequency spectrum. Additionally, the gain can be applied to the energy of the high frequency excitation spectrum generated so that the energy of the generated high frequency excitation spectrum is matched to the inversely quantized energy.

8 is a block diagram illustrating a configuration of a low-frequency spectrum transform unit (710 in FIG. 7) according to an embodiment, and may include an operation unit 810. FIG.

Referring to FIG. 8, the operation unit 810 may perform a predetermined operation process on the decoded low-frequency spectrum based on the excitation class to generate a modified low-frequency spectrum. Here, the decoded low-frequency spectrum may correspond to a noise-filtered processed spectrum, an anti-sparseness processed spectrum, or an inverse-quantized low-frequency spectrum to which no noise is added. The predetermined arithmetic processing may mean a process of determining weights according to the excitation class and mixing the decoded low-frequency spectrum and the random noise based on the determined weights. The predetermined calculation process may include a multiplication process and an addition process. The random noise may be generated in various known ways, for example, using a random seed. On the other hand, the operation unit 810 may further include a process of matching the level of the whitened low-frequency spectrum and the random noise to a similar level prior to the predetermined operation processing.

9 is a block diagram showing a configuration of a low-frequency spectrum transformer (710 in FIG. 7) according to another embodiment, and may include a whitening unit 910, an arithmetic unit 930, and a level adjusting unit 950. Here, the level adjusting unit 950 may be optionally provided.

Referring to FIG. 9, the whitening unit 910 may perform whitening on the decoded low frequency spectrum. Here, noise remaining in the decoded low frequency spectrum may be added by noise filling processing or anti-sparseness processing. The noise addition may be selectively performed on a subband basis. The whitening process performs normalization based on the envelope information of the low frequency spectrum, and various known methods can be applied. Specifically, the normalization process may correspond to calculating the envelope from the low frequency spectrum and dividing the low frequency spectrum by the envelope. The whitening process can be performed so that the shape of the spectrum is flat, but the fine structure of the internal frequency is maintained. On the other hand, the window size for the normalization process can be determined according to the signal characteristics.

The operation unit 930 can perform a predetermined operation process on the whitened low frequency spectrum based on the excitation class to generate the modified low frequency spectrum. The predetermined arithmetic processing may mean a process of determining a weight according to the excitation class and mixing the whitened low-frequency spectrum and the random noise based on the determined weight. The operation unit 930 can operate in the same manner as the operation unit 810 of FIG.

10 is a block diagram showing the configuration of a low-frequency spectrum transformer (710 in FIG. 7) according to another embodiment, and may include a dynamic range controller 1010. FIG.

Referring to FIG. 10, the dynamic range controller 1010 can generate a modified low-frequency spectrum by controlling the dynamic range of the decoded low-frequency spectrum based on the excitation class. Here, the dynamic range may mean a spectrum amplitude.

11 is a block diagram showing the configuration of a low-frequency spectrum transformer (710 in FIG. 7) according to another embodiment, and may include a whitening unit 1110 and a dynamic range controller 1130.

Referring to FIG. 11, the whitening unit 1110 may operate in the same manner as the whitening unit 910 of FIG. That is, the whitening unit 1110 may perform whitening on the decoded low frequency spectrum. Here, noise remaining in the decoded low frequency spectrum may be added by noise filling processing or anti-sparseness processing. The noise addition may be selectively performed on a subband basis. The whitening process performs normalization based on the envelope information of the low frequency spectrum, and various known methods can be applied. Specifically, the normalization process may correspond to calculating the envelope from the low frequency spectrum and dividing the low frequency spectrum by the envelope. The whitening process can be performed so that the shape of the spectrum is flat, but the fine structure of the internal frequency is maintained. On the other hand, the window size for the normalization process can be determined according to the signal characteristics.

The dynamic range control unit 1130 can control the dynamic range of the whitened low frequency spectrum based on the excitation class to generate the modified low frequency spectrum.

12 is a block diagram showing a configuration of a dynamic range control unit 1110 of FIG. 11 according to an embodiment. The code division unit 1210, the control parameter determination unit 1230, the amplitude control unit 1250, Unit 1270 and a sign application unit 1290. [ Here, the random code generation unit 127 may be integrated with the code application unit 129.

Referring to FIG. 12, the code separator 1210 can generate the amplitude, that is, the absolute value spectrum, by removing the sign from the decoded low frequency spectrum.

The control parameter determination unit 1230 can determine the control parameter based on the excitation class. Since the excitation class is information related to the tonal characteristic or the flat characteristic, it is possible to determine a control parameter capable of adjusting the amplitude of the absolute value spectrum based on the excitation class. The amplitude of the absolute value spectrum can be expressed as a dynamic range or a peak-valley interval. According to one embodiment, the control parameter determination unit 1130 can determine control parameters of different values corresponding to the excitation class. For example, it can be assigned as a control parameter of 0.2 for an excursion class associated with voice characteristics, 0.05 for an excursion class associated with a tonal characteristic, and 0.8 for an excursion class associated with a noisy characteristic. According to this, in the case of a frame having a noise characteristic in a high frequency band, the amplitude adjustment degree can be increased.

The amplitude adjuster 1250 can adjust the amplitude of the low frequency spectrum, that is, the dynamic range, based on the control parameter determined by the control parameter determiner 1230. At this time, the larger the control parameter value, the more the dynamic range is adjusted. According to one embodiment, the dynamic range can be adjusted by adding an amplitude of a predetermined magnitude to the original absolute value spectrum. The amplitude of the predetermined magnitude may correspond to a value obtained by multiplying the difference between the amplitude of each frequency bin of a specific band of the absolute value spectrum and the average amplitude of the corresponding band by a control parameter. The amplitude adjuster 1250 can process the low frequency spectrum by configuring bands of the same size. According to one embodiment, each band may be configured to include 16 spectral coefficients. The average amplitude is calculated for each band, and the amplitude of each frequency bin included in each band can be adjusted based on the average amplitude of each band and the control parameter. For example, a frequency bin with an amplitude greater than the average amplitude of the band may reduce its amplitude, and a frequency bin with an amplitude less than the average amplitude of the band may mean increasing its amplitude. At this time, the degree of adjustment of the dynamic range may vary depending on the excitation class. Specifically, the dynamic range control can be performed according to the following equation (1).

Here, S '[i] is the amplitude of the frequency bin i whose dynamic range is controlled, S [i] is the amplitude of the frequency bin i, m [k] is the average amplitude of the band to which the frequency bin i belongs, Respectively. According to one embodiment, each amplitude may represent an absolute value. According to this, the dynamic range control can be performed on a spectral coefficient of a band, that is, on a frequency bin basis. The average amplitude is calculated on a band-by-band basis, and the control parameter can be applied on a frame-by-frame basis.

On the other hand, each band can be configured based on the starting frequency at which the transmission is to be performed. For example, each band may be configured to include 16 frequency bins beginning with the transmission frequency bin 2. Specifically, in the case of SWB, there are nine bands ending at frequency band 145 at 24.4 kbps, and eight bands ending at frequency bin 129 at 32 kbps. In case of FB, there are 19 bands ending in frequency bin 305 at 24.4 kbps, and 18 bands ending at frequency bin 289 at 32 kbps.

The random code generation unit 1270 can generate a random code based on the excitation class when it is determined that the random code is necessary. The random code can be generated on a frame-by-frame basis. According to one embodiment, a random code may be applied in the case of an excitation class associated with the noisy characteristic.

The code application unit 1290 may generate a modified low frequency spectrum by applying one of the random codes or the original codes to the low frequency spectrum in which the dynamic range is adjusted. Here, the original code may be a code removed from the code separator 1210. According to one embodiment, a random code may be applied for an excitation class associated with the noisy characteristic, and an original code for an excitation class associated with the tonal characteristic or an excitation class associated with the voice characteristic. Specifically, the random code can be applied to a frame determined to be noisy, and the original code can be applied to a frame judged to be tuned or a frame judged to be a voice signal.

13 is a block diagram illustrating a configuration of a high frequency excitation spectrum generation unit 730 according to an embodiment, and may include a spectrum patching unit 1310 and a spectrum adjustment unit 1330. FIG. Here, the spectrum controller 1330 may be optionally provided.

Referring to FIG. 13, the spectrum patching unit 1310 may fill the spectrum into an empty high band by patching, for example, transferring, copying, mirroring, or folding the modified low frequency spectrum to a high band. According to the embodiment, a modified spectrum in the source band 50 to 3250 Hz is copied in the 8000 to 11200 Hz band, a modified spectrum in the same source band 50 to 3250 Hz is copied in the 11200 Hz to 14400 Hz band, The modified spectrum at the source band of 2000 to 3600 Hz can be copied in the 14400 to 16000 Hz band. Through this process, a high frequency excitation spectrum can be generated from the modified low frequency spectrum.

The spectrum adjusting unit 1330 can adjust the high frequency excitation spectrum provided from the spectrum patching unit 1310 to resolve the discontinuity of the spectrum at the boundary between the patched bands performed in the spectral patching unit 1310. [ According to the embodiment, the spectrum around the boundary position of the high frequency excitation spectrum provided from the spectrum patching unit 1310 can be utilized.

The generated high frequency excitation spectrum or the adjusted high frequency excitation spectrum and the decoded low frequency spectrum are combined, and the combined spectrum can be generated as a time domain signal through an inverse transformation process. The inverse transform process may be performed in advance for each of the high frequency excitation spectrum and the decoded low frequency spectrum and then combined. Meanwhile, IMDCT (Inverse Modified Discrete Cosine Transform) may be applied to the inverse transform process, but the present invention is not limited thereto.

It is possible to restore the overlapped portion of the frequency band in the spectrum combining process through the overlap add processing. Or a part where the frequency bands overlap in the spectrum combining process, based on the information transmitted through the bit stream. Alternatively, the processing based on the overlap add processing or the transmitted information may be selectively applied according to the environment on the receiving side, or may be restored based on the weight.

FIG. 14 is a diagram for explaining smoothing processing on a weight at a band boundary; FIG. Referring to FIG. 14, since the weights of the K + 2 bands and the weights of the K + 1 bands are different from each other, it is necessary to perform smoothing at the band boundary. In the example of FIG. 14, the K + 1 band does not perform the smoothing but performs the smoothing only in the K + 2 band. The reason for this is that if smoothing is performed in the K + 1 band, since the weight value (Ws (K + 1)) in the K + 1 band is 0, And the random noise in the K + 1 band must be considered. That is, a weight of 0 indicates that random noise is not taken into consideration in generating a high frequency excitation spectrum in the corresponding band. This is for extreme tonal signals and is intended to prevent noise from being inserted into the valley section of the harmonic signal due to random noise.

Next, when a method such as VQ is applied in a manner different from the low-frequency energy transmission method, the low-frequency energy is transmitted using lossless coding after scalar quantization, and the high-frequency energy is quantized by another method Lt; / RTI > In such a case, the last band of the low frequency coding area R0 and the starting band of the BWE area R1 may be overlapped with each other. In addition, the band structure of the BWE area R1 may be configured in a different manner to have a more dense band allocation structure.

For example, the last band of the low-frequency coded region R0 may be configured up to 8.2 kHz, and the start band of the BWE region R1 may be configured to start from 8 kHz. In this case, an overlapping region is generated between the low-frequency coding region R0 and the BWE region R1. As a result, two decoded spectra can be generated in the overlapping region. One is a spectrum generated by applying a low-frequency decoding scheme, and the other is a spectrum generated by a high-frequency decoding scheme. An overlap add method can be applied so that the two spectra, that is, the transition between the low frequency spectrum and the high frequency spectrum, are smoother. For example, while using two spectra at the same time, a spectrum close to the low frequency side of the overlapped region raises the contribution of the spectrum generated by the low frequency method, and a spectrum near the high frequency side increases the contribution of the spectrum generated by the high frequency method, Can be reconstructed.

For example, if the last band of the low-frequency coding region R0 starts at 8 kHz, and the starting band of the BWE region R1 starts at 8 kHz, if a spectrum of 640 samples is formed at a sampling rate of 32 kHz, Eight spectra overlap and eight spectra can be generated as shown in Equation 2 below.

는 저주파 방식으로 복호화된 스펙트럼,

는 고주파 방식으로 복호화된 스펙트럼, L0는 고주파의 시작 스펙트럼 위치, L0~L1은 오버래핑된 영역, w₀는 기여분을 각각 나타낸다.here,

Is a spectrum decoded in a low frequency manner,

Is the decoded spectrum by a high-frequency manner, L0 is started spectral position of the high-frequency, L0 ~ L1 is the overlapping area, w ₀ represents the contribution respectively.

15 is a view for explaining a contribution used for reconstructing a spectrum existing in an overlapping region after BWE processing in a decoding end according to an embodiment.

15, w _O (k) can selectively apply w _O0 (k) and w _O1 (k), where w _O0 (k) applies the same weighting to the low and high frequency decoding schemes , w _O1 (k) are methods for applying a larger weight to the high-frequency decoding scheme. The selection criterion for both w _O (k) varies, but for example, whether there is a spectral coefficient or a pulse in the low-frequency overlapping band. When spectral coefficients or pulses are coded in a low-frequency overlapping band, w _O0 (k) is used to make contributions to the spectrum generated at the low frequencies up to near L1 and to reduce high frequency contributions. Basically, the spectrum generated by the actual coding scheme rather than the spectrum of the signal generated by the BWE may be higher in terms of proximity to the original signal. A method of enhancing the contribution of the spectrum closer to the original signal in the overlapping band can be applied, thereby improving the smoothing effect and sound quality.

16 is a block diagram illustrating a configuration of a multimedia device including a decoding module according to an embodiment of the present invention.

The multimedia device 1600 shown in FIG. 16 may include a communication unit 1610 and a decryption module 1630. The storage unit 1650 may store the restored audio signal according to the use of the restored audio signal obtained as a result of the decoding. In addition, the multimedia device 1600 may further include a speaker 1670. That is, the storage unit 1650 and the speaker 1670 may be optionally provided. Meanwhile, the multimedia device 1600 shown in FIG. 16 may further include an encoding module (not shown), for example, an encoding module performing a general encoding function or an encoding module according to an embodiment of the present invention . Here, the decoding module 1630 may be implemented as at least one processor (not shown) integrated with other components (not shown) included in the multimedia device 1600.

16, the communication unit 1610 receives at least one of an encoded bit stream and an audio signal provided from the outside or a reconstructed audio signal obtained as a result of decoding by the decoding module 1630 and an audio bit stream One can be transmitted. The communication unit 1610 may be a wireless communication unit such as a wireless Internet, a wireless intranet, a wireless telephone network, a LAN, a Wi-Fi, a WFD, a WiFi Direct, a 3G, a 4G, Wireless network such as Bluetooth, Infrared Data Association (RFID), Radio Frequency Identification (RFID), Ultra WideBand (UWB), Zigbee and Near Field Communication, And is configured to transmit / receive data to / from an external multimedia device through a wired network.

According to one embodiment, the decryption module 1630 may receive the bitstream provided through the communication unit 1610 and decode the audio spectrum included in the bitstream. The decoding process may be performed using the above-described decoding apparatus or a decoding method to be described later, but is not limited thereto.

The storage unit 1650 may store the reconstructed audio signal generated by the decoding module 1630. Meanwhile, the storage unit 1650 may store various programs necessary for the operation of the multimedia device 1600.

The speaker 1670 can output the restored audio signal generated by the decoding module 1630 to the outside.

17 is a block diagram illustrating a multimedia device including a coding module and a decoding module according to an embodiment of the present invention.

The multimedia device 1700 shown in FIG. 17 may include a communication unit 1710, an encoding module 1720, and a decryption module 1730. The storage unit 1740 may further include an audio bitstream or a restored audio signal according to the use of the audio bitstream obtained as a result of encoding or the reconstructed audio signal obtained as a decoding result. In addition, the multimedia device 1700 may further include a microphone 1750 or a speaker 1760. Here, the encoding module 1720 and the decryption module 1730 may be implemented as at least one processor (not shown) integrated with other components (not shown) included in the multimedia device 1700.

The detailed description of the components that are duplicated in the multimedia device 1600 shown in FIG. 16 among the components shown in FIG. 17 will be omitted.

The encoding module 1720 may encode an audio signal of a time domain provided through the communication unit 1710 or the microphone 1750 according to an embodiment. The encoding process can be performed using the above-described encoding device, but is not limited thereto.

The microphone 1750 may provide a user or an external audio signal to the encoding module 1720.

The multimedia devices 1600 and 1700 shown in Figs. 16 and 17 are connected to a broadcasting or music dedicated device including a voice communication dedicated terminal including a telephone, a mobile phone, and the like, a TV, an MP3 player, But is not limited to, a fusion terminal device of a broadcast or music exclusive apparatus. In addition, the multimedia devices 1600 and 1700 can be used as a client, a server, or a converter disposed between a client and a server.

When the multimedia devices 1600 and 1700 are mobile phones, for example, a display unit for displaying information processed in a user input unit such as a keypad or the like, a user interface or a mobile phone (not shown), a processor As shown in FIG. The mobile phone may further include a camera unit having an image pickup function and at least one or more components for performing functions required in the mobile phone.

When the multimedia devices 1600 and 1700 are, for example, TVs, a user input unit such as a keypad, a display unit for displaying received broadcast information, and a processor for controlling overall functions of the TV may be further included . In addition, the TV may further include at least one or more components that perform the functions required by the TV.

18 is a flowchart for explaining the operation of the high-frequency decoding method according to an embodiment. The method shown in FIG. 18 may be performed in the high-frequency decoding unit 670 of FIG. 6 or may be performed by a separate processor.

Referring to FIG. 18, in step 1810, an excitation class is decoded. Here, a class may be generated at the encoder end and sent to the decoder end as a bitstream. On the other hand, the excitation class can be separately generated and used at the decoder end. Here the class can be obtained on a frame basis.

In step 1830, the low-frequency spectrum decoded from the quantization index of the low-frequency spectrum included in the bitstream may be received. The quantization index may be, for example, an inter-band difference index other than the lowest frequency band. The quantization index of the low frequency spectrum can be vector dequantized, for example. As the vector dequantization method, Pyramid Vector Quantization (PVQ) can be used but is not limited thereto. A noise filling process may be performed on the inverse quantization result to generate a decoded low frequency spectrum. The noise filling process is to fill the gaps present in the spectrum by being quantized to zero. Pseudo random noise can be inserted into the gap. The frequency blanking period in which the noise filling process is processed can be set in advance. The amount of noise inserted into the gap can be controlled by parameters transmitted in the bitstream. The noise-filtered low-frequency spectrum can additionally be subjected to denormalization. Anti-sparseness processing may be additionally performed on the noise-filtered low-frequency spectrum. For anti-sparseness processing, a coefficient having a random code and amplitude of a certain magnitude may be inserted into the coefficient portion remaining zero in the noise-filtered low-frequency spectrum. The anti-sparseness low-frequency spectrum can additionally be energy-controlled based on the low-band dequantized envelope.

In step 1850, the decoded low-frequency spectrum can be modified based on the excitation class. The decoded low frequency spectrum can be one of an inverse quantized spectrum, a noise-filled spectrum, or an anti-sparseness spectrum. The amplitude of the decoded low frequency spectrum can be adjusted by the excitation class. For example, the amplitude reduction can be determined by the excitation class.

In step 1870, a high frequency excitation spectrum can be generated using the modified low frequency spectrum. The modified low-frequency spectrum can be fetched into the high-band required for bandwidth extension to generate a high-frequency excitation spectrum. An example of the patching method is a method of copying or folding a preset section to a high band.

19 is a flowchart for explaining the operation of the low frequency spectrum transform method according to an embodiment. The method shown in FIG. 19 corresponds to step 1850 of FIG. 18, or may be implemented independently. On the other hand, the method shown in Fig. 19 may be performed in the low-frequency spectrum transforming unit 710 of Fig. 7 or may be performed by a separate processor.

Referring to FIG. 19, in step 1910, the degree of amplitude control can be determined based on the excitation class. Specifically, in step 1910, a control parameter may be generated based on the excitation class to determine the degree of amplitude control. According to an embodiment, the value of the control parameter may be determined depending on whether the excursion class represents a voice characteristic, a tonal characteristic or a non-tonal characteristic.

In step 1930, the amplitude of the low frequency spectrum can be adjusted based on the determined degree of amplitude control. Compared with the case where the class exhibits a voice characteristic or a tonal characteristic, when the exciting class exhibits a non-tonal characteristic, a larger value of the control parameter is generated, so that the amplitude reduction can be increased. An example of the amplitude control may be to reduce the difference between the amplitude of each frequency bin, e.g. Norm, and the average norm value of the band, multiplied by the control parameter.

In step 1950, the sign can be applied to the amplitude-controlled low frequency spectrum. Depending on the class here, the original code or random code can be applied. For example, when the excursion class indicates a speech characteristic or a tonal characteristic, random encoding may be applied when the original code indicates that the excursion class exhibits non-tonal characteristics.

In step 1970, the low frequency spectrum to which the sign is applied can be generated as a modified low frequency spectrum in step 1950.

The method according to the above embodiments can be implemented in a general-purpose digital computer that can be created as a program that can be executed by a computer and operates the program using a computer-readable recording medium. In addition, a data structure, a program command, or a data file that can be used in the above-described embodiments of the present invention can be recorded on a computer-readable recording medium through various means. A computer-readable recording medium may include any type of storage device that stores data that can be read by a computer system. Examples of the computer-readable recording medium include magnetic media such as a hard disk, a floppy disk and a magnetic tape, optical media such as a CD-ROM and a DVD, a floppy disk, Such as magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The computer-readable recording medium may also be a transmission medium for transmitting a signal designating a program command, a data structure, and the like. Examples of program instructions may include machine language code such as those produced by a compiler, as well as high level language code that may be executed by a computer using an interpreter or the like.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. Various modifications and variations are possible in light of the above teachings. Accordingly, the scope of the present invention is not in the above description, but is expressed in the claims, and all of its equivalents or equivalent variations fall within the scope of the technical idea of the present invention.

610 ... demultiplexing unit 630 ... BWE parameter decoding unit
650 ... low frequency decoding unit 670 ... high frequency decoding unit
710 ... low frequency spectrum deformation section 730 ... high frequency excitation spectrum generation section
1210 ... code separator 1230 ... control parameter determiner
1250 ... amplitude adjuster 1270 ... random code generator
1290 ... code application unit

Claims (15)

Decoding the class here;
Modifying the decoded low frequency spectrum based on the excitation class; And
And generating a high frequency excitation spectrum based on the modified low frequency spectrum. The high frequency decoding method according to claim 1, wherein the excitation class is included in a bitstream on a frame-by-frame basis. The high-frequency decoding method according to claim 1, wherein the modifying the low-frequency spectrum determines an amplitude adjustment degree based on the excitation class. The high frequency decoding method according to claim 1, wherein modifying the low frequency spectrum comprises adjusting the dynamic range of the decoded low frequency spectrum based on the excitation class. 2. The method of claim 1, wherein transforming the low-
Generating a control parameter based on the excitation class; And
And adjusting the amplitude of the low frequency spectrum based on the control parameter. 6. The method of claim 5, wherein modifying the low frequency spectrum further comprises normalizing the decoded low frequency spectrum, and adjusting the amplitude of the normalized low frequency spectrum based on the control parameter. 6. The method of claim 5, wherein the adjusting the amplitude of the low frequency spectrum is performed using the difference between the amplitude of the spectral coefficient included in the specific band and the amplitude average of the band and the control parameter. 6. The method of claim 5, wherein modifying the low-frequency spectrum further comprises applying one of a random code and an original code based on an excitation class for an amplitude-controlled low-frequency spectrum. The high frequency decoding method according to claim 5, wherein when the excitation class is related to a voice characteristic or a tonal characteristic, the original code is applied to the amplitude-controlled low frequency spectrum. 6. The method of claim 5, wherein applying the random code to the low frequency spectrum when the excitation class is related to the non-tonal characteristic. The method of claim 1, wherein the decoded low-frequency spectrum is a noise-filtered spectrum or an anti-sparseness spectrum. And at least one processor for decoding the excitation class, modifying the decoded low-frequency spectrum based on the excitation class, and generating a high-frequency excitation spectrum based on the modified low-frequency spectrum. 13. The system of claim 12, wherein the processor
A parameter decoding unit for decoding the excitation class; And
A low frequency spectrum transformer for adjusting the amplitude of the decoded low frequency spectrum based on the excitation class to generate the modified low frequency spectrum; And
And a high frequency excitation spectrum generation unit for generating the high frequency excitation spectrum based on the modified low frequency spectrum. 13. The high-frequency decoding apparatus according to claim 12, wherein the processor determines the degree of adjustment of the decoded low-frequency spectrum dynamic range based on the excitation class. 13. The high-frequency decoding apparatus of claim 12, wherein the processor adjusts the dynamic range of the decoded low frequency spectrum much more than when the excitation class indicates a non-speech characteristic or a tonal characteristic, when the excitation class indicates non-tonal characteristics.

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