JP4313993B2 - Audio decoding apparatus and audio decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decode a wide-band audio signal of high quality at a low bit rate. <P>SOLUTION: Low-band component information separated by a bit stream separating means is decoded into a low-band time signal representing a low-band component. The obtained low-band time signal is divided into a plurality of low-band subband signals. A band expanding means generates a high-band subband signal according to the low-band subband signals and high-band component information. The low-band and high-band subband signals are put together by a composition subband filter into a time area composite signal. According to sine-wave addition information, a signal of a time area representing a sine wave having a desired frequency and a desired amplitude characteristic is generated and put together with the time area composite signal. Through this constitution, a decoded signal more faithful to an input signal can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a band expansion system that generates a wideband audio signal from a narrowband audio signal by adding auxiliary information with a small amount of information, and for improving the quality of the reproduced signal and reducing the amount of computation in the system. Related to technology.
[0002]
[Prior art]
As a technique that can encode a general acoustic signal with a small amount of information and obtain a high-quality reproduced signal, a method that uses band division coding is widely known. This is because the input acoustic signal is divided into a plurality of frequency band signals using a band division filter, or converted to a frequency axis signal using time-frequency conversion such as Fourier transform, and then the frequency axis. This can be realized by dividing the data into a plurality of bands and assigning appropriate coded bits to the divided bands. The reason why a high-quality reproduction signal can be obtained from a code with a small amount of information by using band division coding is that processing based on human auditory characteristics can be performed at the coding stage. In general, human hearing is less sensitive to sounds with a high frequency of about 10 kHz or more, and sounds with low levels are less likely to be detected. Also, a phenomenon called frequency masking is well known, and when a high level sound exists in a specific frequency band, a low level sound in the peripheral band becomes difficult to detect. For such parts that are difficult to detect due to auditory characteristics, even if bit allocation is performed and encoding is performed, the quality of the reproduced signal is hardly affected, and encoding does not make sense. Conversely, by reassigning the coded bits assigned to this part without considering the auditory characteristics to other auditory sensitive parts, the auditory sensitive parts are encoded in detail and the reproduced signal is reproduced. Can improve the quality. As a typical example of encoding using such band division, there is ISO international standard MPEG-4 AAC (ISO / IEC 14496-3), and at a bit rate of about 96 kbps, a wide-band stereo signal of 16 kHz or more is received. It is possible to encode with high quality.
[0003]
However, when the bit rate is reduced to, for example, about 48 kbps, the band that can be encoded with high quality is about 10 kHz or less, and the sound is audibly sounded. As a method for compensating for such sound quality degradation due to band limitation, for example, “Digital Radio Monaural (DRM) recommended by ETSI (European Telecommunications Standards Institute)” is described in System Specification 101 (ETSI TS 101, 9). There is a technique called (Spectral Band Replication).
[0004]
FIG. 7 is a diagram illustrating an example of a decoder that performs band extension by SBR. Hereinafter, the operation will be described with reference to the drawings. The input bit stream 706 is separated into low-frequency component information 707, high-frequency component information 708, and sine wave additional information 709 by the bit stream separation means 701. The low frequency component information 707 is information encoded by using an encoding method such as MPEG-4 AAC, for example, and is decoded by the low frequency decoding means 702 to generate a time signal representing the low frequency component. The generated time signal representing the low frequency component is divided into a plurality (M) of subbands in the analysis filter bank 703 and input to the band extending means 704. The band extending unit 704 compensates for the high frequency component lost due to the band limitation by copying the low frequency subband signal representing the low frequency component to the high frequency subband. Here, the high frequency component information 708 input to the band extending means 704 includes gain information for the high frequency sub-band to be compensated, and the gain is adjusted for each generated high frequency sub-band. Further, according to the sine wave additional information 709, a gain-controlled sine wave is added to each high frequency sub-band. The high frequency sub-band signal generated in the band extending unit 704 is input to the synthesis filter bank 705 together with the low frequency sub-band signal, and is subjected to band synthesis to generate an output signal 710. At this time, the number of subbands on the synthesis filter bank side does not need to match the number of subbands on the analysis filter side. For example, if the relationship of N = 2M is established in FIG. 7, the sampling frequency of the output signal is twice the sampling frequency of the time signal input to the analysis filter bank.
[0005]
In the above configuration, since the information included in the high-frequency component information 708 or the sine wave additional information 709 is only information related to gain control, the amount of information is very small compared to the low-frequency component information 707 including spectrum information. I only need it. Therefore, this is a method suitable for encoding a wideband signal at a low bit rate.
[0006]
[Problems to be solved by the invention]
However, the above configuration is subject to limitations due to the subband filter, particularly when a sine wave is added. For example, when adding a sine wave to a high frequency sub-band, when adding a sine wave to a frequency corresponding to the boundary with an adjacent sub-band filter, the sine wave is applied to two adjacent sub-bands. A component must be added, and since the amplitude value and phase for the sine wave component influence each other, it is expected that a large amount of calculation is required to derive the component. Therefore, in practice, a sine wave is injected into the center frequency of each subband, which is a constraint condition, and it is difficult to obtain reproduced sound faithful to the input signal. Further, in the band extension system to which the present invention is applied, a high-frequency component signal to which a sine wave is added requires a large amount of information when the phase component is encoded in detail and information is transferred. In general, the phase component is not encoded in order to reduce the amount. Therefore, the phase component is unknown on the decoding side, and it is necessary to perform the decoding process only from the energy. In this case, the signal phase is generally considered using a complex coefficient subband filter, but a real coefficient subband filter may be used to reduce the amount of computation. However, it is difficult to control the phase in the real-band coefficient sub-band filter as compared to the control in the complex-band coefficient sub-band filter.
[0007]
The present invention has been made in view of such a conventional problem, and is configured to perform addition of a sine wave to a signal in a time domain, so that the sine wave frequency caused by the subband filter can be reduced. It is an object of the present invention to provide a decoding method that solves the problems related to limitations and phase and enables decoding of a signal that is as faithful as possible to the input signal.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention is to divide each encoded signal from a bit stream obtained by multiplexing audio signal information that is divided into frames of a predetermined time length and further divided into a plurality of subbands. Bit stream separation means for separating information, low frequency decoding means for decoding a time signal representing a low frequency component from the separated low frequency encoded information, and a plurality of low frequency sub signals An analysis subband filter that divides the signal into band signals, band expansion means for generating a high frequency subband signal from the low frequency subband signal and the high frequency encoded information separated from the low frequency subband signal, and low frequency and high frequency subband signals A combined subband filter that combines to obtain a time domain signal and a sine wave generator that generates a time domain signal representing a sine wave of the desired frequency and amplitude characteristics from the separated sine wave additional information. Means, frequency adjusting means for adjusting the frequency of the sine wave generated from the sine wave generating means to be an integral multiple of the frequency of the decoded low-frequency signal, and the time obtained from the synthesis filter bank There is provided time signal synthesizing means for synthesizing the area signal and the sine wave obtained from the sine wave generating means to obtain an output audio signal.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The audio decoding method according to the first embodiment of the present invention is based on a bitstream obtained by multiplexing audio signal information that is divided into frames of a predetermined time length and further divided into a plurality of subbands and encoded. A bit stream separating means for separating each encoded information; a low-frequency decoding means for decoding a time signal representing a low-frequency component from the separated low-frequency encoded information; and a plurality of decoded low-frequency signals An analysis subband filter that divides the signal into low-frequency subband signals, band expansion means for generating a high-frequency subband signal from the low-frequency subband signal and the high-frequency encoded information separated from the low-frequency subband signal, A synthesized subband filter that synthesizes subband signals to obtain a time domain signal, and a time domain signal that represents a sine wave of desired frequency and amplitude characteristics from the separated sine wave additional information A sine wave generating means for generating and a time signal synthesizing means for synthesizing a plurality of time domain signals are provided, and the time domain signal obtained from the synthesis filter bank and the sine wave obtained from the sine wave generating means are synthesized. It is the structure made to do.
[0010]
The audio decoding method according to the second embodiment of the present invention differs from the audio decoding method according to the first embodiment of the present invention in that the low frequency signal obtained from the low frequency decoding means is used. Analyzing and detecting the periodicity of the signal and its frequency, and a periodicity adjusting means for controlling the sine wave generating means based on the detected frequency, and generating according to the characteristics of the low frequency signal In this configuration, the frequency of the generated sine wave is adaptively controlled.
[0011]
The audio decoding method according to the third embodiment of the present invention is a method of analyzing the low frequency signal and detecting a change in the signal with respect to the audio decoding method according to the first embodiment of the present invention. The signal change detecting means is provided, and the amplitude control position of the generated sine wave is adaptively controlled according to the characteristics of the low frequency signal.
[0012]
Hereinafter, an audio decoding method according to an embodiment of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a configuration diagram showing a decoding method according to Embodiment 1 of the present invention. The difference from the conventional example shown in FIG. 7 described above is that in the conventional example, the sine wave additional information 709 is directly input to the band expanding means 704 and the sine wave addition process is performed on the subband signal. On the other hand, in the embodiment of the present invention, the time domain sine wave generation means 106 is provided to generate the time domain sine wave signal 114 according to the sine wave additional information 112, and the time output from the synthesis filter bank 105. It is configured to be added to the region composite signal 116.
[0013]
The input bit stream 109 is separated into low-frequency component information 110, high-frequency component information 111, and sine wave additional information 112 by the bit stream separation means 101. The low frequency component information 110 is information encoded by using an encoding method such as MPEG-4 AAC, for example, and is decoded by the low frequency decoding means 102 to generate a time signal representing the low frequency component. The generated time signal representing the low frequency component is divided into a plurality (M) of subbands in the analysis filter bank 103 and input to the band extending means 104. The band extending means 104 compensates for the high frequency component lost due to the band limitation by copying the low frequency subband signal representing the low frequency component to the high frequency subband. Here, the high frequency component information 111 input to the band extending means 104 includes gain information for the high frequency sub-band to be compensated, and the gain is adjusted for each generated high frequency sub-band. The high frequency sub-band signal generated in the band extending means 104 is input to the synthesis filter bank 105 together with the low frequency sub-band signal, and is subjected to band synthesis to generate a time domain synthesized signal 116. Further, the time domain sine wave generating unit 106 generates a parameter for adjusting the characteristics of the sine wave generated by the sine wave adjusting unit 107 based on the input sine wave additional information 112 and then the sine wave generating unit 108. A desired sine wave is generated and output as a time domain sine wave signal 114. The time domain synthesized signal 116 and the time domain sine wave signal 114 are synthesized as a time signal to become an output signal 115.
[0014]
Here, the configuration and operation of the time domain sine wave generating means 106 will be described in detail. FIG. 2 is a diagram showing the configuration of the time domain sine wave generating means 106. The sine wave adjusting unit 107 includes an amplitude adjusting unit 201, a timing adjusting unit 202, and a rough shape generating unit 204. The amplitude adjusting unit 201 refers to the sine wave additional information 205 and outputs amplitude information 207 for controlling the amplitude of the generated sine wave. Similarly, the timing adjustment unit 202 refers to the sine wave additional information 205 and outputs timing information 208 for controlling the timing of the generated sine wave change. Subsequently, the outline generation unit 204 generates an outline of a sine wave from the amplitude information 207 and the timing information 208. FIG. 3 is a diagram illustrating the outline of the generated sine wave. Usually, the outline of the sine wave has a stepped shape like the outline 301 before interpolation shown in (a) by combining the timing information t indicating a certain time and the corresponding amplitude information A. Based on the sine wave frequency information 206 included in the sine wave additional information 205, a desired time-amplitude characteristic is obtained by applying the above outline to a sine wave having a constant amplitude generated by the sine wave generating unit 203. A time-domain sine wave 209 can be generated.
[0015]
By adopting such a configuration, it is possible to set the frequency of the added sine wave without being limited by the frequency of the sine wave by the subband filter, so that a high-quality output signal closer to the input signal is obtained. be able to. Further, since the added sine wave is generated as a time signal, phase control is also easy.
[0016]
In addition, when the information for adding a plurality of sine waves is included in the sine wave additional information, a sine wave having a plurality of frequencies is sequentially generated, and the corresponding outline is applied to each sine wave. After that, all the sine waves may be synthesized. Corresponding outlines may be the same for all sine waves, or may have different shapes.
[0017]
In addition, when generating the approximate shape of the sine wave in the approximate shape generation means 204, by performing interpolation processing using amplitude information between adjacent frames, it is possible to suppress a sudden change in the signal and improve the sound quality. In the outline after interpolation shown in (b) of FIG. 3, there is no point where the amplitude existing in the outline 301 before interpolation shown in (a) changes suddenly, so that the volume of the output signal changes smoothly. The sound quality on hearing is improved. The same processing can be performed by adding a sine wave to a conventional subband signal. In this case, the unit in the time direction in which the amplitude can be controlled is a subsample (sample in the subband signal), and the interpolation accuracy is reduced. Will do. In this configuration, the output signal can be interpolated in units of samples, and a higher quality output signal can be obtained.
[0018]
Further, frequency interpolation is also possible as interpolation between adjacent frames. As with the amplitude information, the output signal can be interpolated in units of samples, and an output signal with higher sound quality can be obtained by smoothly changing the frequency of the added sine wave.
[0019]
(Embodiment 2)
FIG. 4 is a configuration diagram showing a decoding method according to Embodiment 2 of the present invention. In the configuration of the second embodiment, the frequency analysis means 410 and the frequency adjustment means 411 are provided in the time domain sine wave generation means of the first embodiment shown in FIG. 2, and the low frequency time signal 412 is analyzed by the frequency analysis means 410. The frequency adjustment unit 411 is configured to adaptively control the frequency of the generated sine wave based on the analysis result. As the low frequency signal 412, for example, the output of the low frequency decoding means 102 in FIG. 1 is used.
[0020]
Here, the reason for controlling the frequency of the sine wave generated based on the result of analyzing the frequency of the low-frequency signal will be described. FIG. 5 is a diagram showing a spectral distribution of an audio signal. Of the information included in the input bit stream, only the low frequency component information holds the encoding information of the spectrum of the audio signal, and the band limitation indicated by 501 is applied when encoding the low frequency component. Has been. Therefore, the low frequency signal output from the low frequency decoding means includes only a spectrum within the band limit 501 range. In the sine wave addition process, the bandwidth of the audio signal to be decoded is expanded by adding a sine wave to a high frequency exceeding the range of the band limit 501. Usually, the added sine wave has a certain fundamental frequency. A harmonic 503 having a frequency that is an integral multiple of the fundamental wave 502 having This is based on the fact that many of the audio signals that are generally encoded are composed of a set of multiple harmonics. Therefore, the sine wave additional information 405 needs to include frequency information that correctly represents an integral multiple of the fundamental wave 502. For this purpose, a large amount of information needs to be allocated, and the present invention is intended. At very low bit rates, only approximate frequency information can be assigned. As a result, the frequency of the added sine wave is different from that of the integral multiple harmonic 503, leading to a reduction in the quality of the decoded audio signal. On the other hand, in the embodiment of the present invention, the frequency analysis unit 410 analyzes the low-frequency signal 412, and based on the analyzed fundamental frequency, the frequency adjustment unit 411 calculates the frequency of the generated sine wave. Since the control is performed so as to be an integral multiple of the fundamental frequency, the difference between the frequency of the added sine wave and the integral multiple harmonic 503 is eliminated, so that an output signal more faithful to the input signal can be obtained.
[0021]
The frequency analysis unit 410 may be configured to switch whether or not to perform adaptive control of the frequency in the frequency adjustment unit 411 based on the analyzed intensity information of the fundamental frequency.
[0022]
(Embodiment 3)
FIG. 6 is a configuration diagram showing a decoding method according to Embodiment 3 of the present invention. In the configuration of the third embodiment, in the time domain sine wave generating means of the first embodiment shown in FIG. 2, a signal change detecting means 611 is provided, and the signal change detecting means 611 analyzes the low frequency signal 610 for analysis. Based on the result, the timing adjustment means 602 adaptively controls the amplitude control position of the sine wave to be generated. As the low frequency signal 610, for example, the output of the low frequency decoding means 102 in FIG. 1 is used.
[0023]
Here, the reason for controlling the amplitude control position of the sine wave generated based on the analysis of the change in the low-frequency signal will be described. The amplitude of the added sine wave is given as amplitude information at a certain time position t as shown in FIG. In order to represent the input signal as faithfully as possible, it is necessary to set as many amplitude adjustment positions as possible. However, at a low bit rate that is targeted by the decoding apparatus of the present invention, a small number is required to reduce the amount of information. Only the amplitude adjustment position can be installed. The amplitude adjustment position can be selected only from a plurality of predetermined candidate points. For this reason, a shift occurs between the actual change point of the input signal and the amplitude adjustment position, leading to a decrease in the quality of the decoded audio signal. On the other hand, in the embodiment of the present invention, the signal change detection means 611 analyzes the low frequency signal 610, detects the signal change point, and adapts the amplitude adjustment position of the sine wave based on the position information. Therefore, the difference between the change point of the input signal and the amplitude adjustment position is eliminated, and an output signal more faithful to the input signal can be obtained.
[0024]
Note that the amplitude adjustment position control of the sine wave according to the present embodiment can also be applied to high-frequency signal generation in the band extension means 104 shown in FIG. Like the sine wave signal, the amplitude of the high frequency signal is given as amplitude information at a certain time position t. Therefore, the amplitude adjustment position is adapted based on the positional information of the changing point obtained by analyzing the low frequency signal. By performing the control, the deviation between the change point of the input signal and the amplitude adjustment position can be eliminated, and an output signal more faithful to the input signal can be obtained.
[0025]
In the first to third embodiments, the sine wave generation method and the synthesis method based on the sine wave additional information have been described. However, any waveform signal having periodicity is used instead of the sine wave. Also good. Since it is realized as processing for a time domain signal, it can be realized by the same configuration as that of the present embodiment without being influenced by the frequency spectrum distribution of the waveform to be used.
[0026]
【The invention's effect】
According to the present invention, by adding the sine wave to the signal in the time domain, the problem related to the limitation of the sine wave frequency and the phase caused by the subband filter is solved, and the input signal is more faithful. High-quality audio signals can be decoded.
Further, according to the present invention, it is possible to decode a high-quality audio signal faithful to the input signal by adaptively controlling the frequency of the added sine wave based on the analysis result of the low-frequency signal. Become.
In addition, according to the present invention, it is possible to decode a high-quality audio signal that is more faithful to the input signal by adaptively controlling the amplitude control position of the added sine wave based on the analysis result of the low-frequency signal. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of the configuration of an audio decoding apparatus according to the present invention. FIG. 2 is a diagram showing an example of a time domain sine wave generating means according to the present invention. FIG. 4 is a diagram showing an example of a time domain sine wave generating means of the present invention. FIG. 5 is a diagram showing an outline of a sine wave for amplitude adjustment. FIG. 6 is an example of a time domain sine wave generating means of the present invention. FIG. 7 is a diagram showing an example of a conventional audio decoding apparatus.
101 Bit stream separation means 102 Low frequency decoding means 103 Analysis filter bank 104 Band expansion means 105 Synthesis filter bank 106 Time domain sine wave generation means 107 Sine wave adjustment means 108 Sine wave generation means 109 Bit stream 110 Low frequency component information 111 High frequency Component information 112 Sine wave additional information 113 Sine wave adjustment information 114 Time domain sine wave signal 115 Output signal 116 Time domain synthesized signals 201, 401, 601 Amplitude adjustment means 202, 402, 602 Timing adjustment means 203, 403, 603 Sine wave generation Means 204, 404, 604 Outline generation means 205, 405, 605 Sine wave additional information 206, 406, 606 Frequency information 207, 407, 607 Amplitude information 208, 408, 608 Timing information 209, 409, 609 Time domain positive String wave signal 301 General shape before interpolation 302 General shape after interpolation 410 Frequency analysis means 411 Frequency adjustment means 412 Low-frequency signal 501 Band limit 502 Fundamental wave 503 Harmonic wave 504 Integer multiple relationship 610 Low-frequency signal 611 Signal change Detection means

Claims (6)

Bitstream separation means for separating each encoded information from a bitstream obtained by multiplexing audio signal information divided into frames of a predetermined time length and further divided into a plurality of subbands and encoded;
Low frequency decoding means for decoding a time signal representing a low frequency component from the separated low frequency encoding information;
An analysis subband filter that divides the decoded lowband time signal into a plurality of lowband subband signals;
Band extension means for generating a high frequency subband signal from the low frequency subband signal and the separated high frequency encoded information,
A synthesis subband filter that synthesizes low and high frequency subband signals to obtain a time domain signal;
Sine wave generating means for generating a time-domain signal representing a sine wave having a desired frequency and amplitude characteristic from the separated sine wave additional information;
Frequency adjusting means for adjusting the frequency of the sine wave generated from the sine wave generating means to be an integral multiple of the frequency of the decoded low-frequency signal;
An audio decoding device comprising: a time signal synthesis unit that synthesizes a time domain signal obtained from the synthesis filter bank and a sine wave obtained from the sine wave generation unit to obtain an output audio signal. Bitstream separation means for separating each encoded information from a bitstream obtained by multiplexing audio signal information divided into frames of a predetermined time length and further divided into a plurality of subbands and encoded;
Low frequency decoding means for decoding a time signal representing a low frequency component from the separated low frequency encoding information;
An analysis subband filter that divides the decoded lowband time signal into a plurality of lowband subband signals;
Band extension means for generating a high frequency subband signal from the low frequency subband signal and the separated high frequency encoded information,
A synthesis subband filter that synthesizes low and high frequency subband signals to obtain a time domain signal;
Sine wave generating means for generating a time-domain signal representing a sine wave having a desired frequency and amplitude characteristic from the separated sine wave additional information;
Timing adjustment means for adjusting the amplitude change position of the sine wave generated from the sine wave generation means based on the change position of the decoded low-frequency signal;
An audio decoding device comprising: a time signal synthesis unit that synthesizes a time domain signal obtained from the synthesis filter bank and a sine wave obtained from the sine wave generation unit to obtain an output audio signal. A bit stream separation process procedure for separating each encoded information from a bit stream obtained by multiplexing audio signal information divided into a plurality of frames of a predetermined time length and further divided into a plurality of subbands and encoded;
A low frequency decoding processing procedure for decoding a time signal representing a low frequency component from the separated low frequency encoding information;
An analysis subband filtering procedure for dividing the decoded lowband time signal into a plurality of lowband subband signals;
Band extension processing procedure for generating a high frequency subband signal from the low frequency subband signal and the separated high frequency encoded information,
A synthesis subband filter processing procedure for synthesizing the low frequency and high frequency subband signals to obtain a time domain signal,
A sine wave generation processing procedure for generating a time-domain signal representing a sine wave having a desired frequency and amplitude characteristic from the separated sine wave additional information;
A frequency adjustment processing procedure for adjusting the frequency of the sine wave generated in the sine wave generation processing procedure to be an integral multiple of the frequency of the decoded low-frequency signal;
A time signal synthesis processing procedure for obtaining an output audio signal by synthesizing the time domain signal obtained from the synthesis filter bank processing procedure and the sine wave obtained in the sine wave generation processing procedure. Decryption method. A bit stream separation process procedure for separating each encoded information from a bit stream obtained by multiplexing audio signal information divided into a plurality of frames of a predetermined time length and further divided into a plurality of subbands and encoded;
A low frequency decoding processing procedure for decoding a time signal representing a low frequency component from the separated low frequency encoding information;
An analysis subband filtering procedure for dividing the decoded lowband time signal into a plurality of lowband subband signals;
Band extension processing procedure for generating a high frequency subband signal from the low frequency subband signal and the separated high frequency encoded information,
A synthesis subband filter processing procedure for synthesizing the low frequency and high frequency subband signals to obtain a time domain signal,
A sine wave generation processing procedure for generating a time-domain signal representing a sine wave having a desired frequency and amplitude characteristic from the separated sine wave additional information;
A timing adjustment processing procedure for adjusting the amplitude change position of the sine wave generated in the sine wave generation processing procedure based on the change position of the decoded low-frequency signal;
A time signal synthesis processing procedure for obtaining an output audio signal by synthesizing the time domain signal obtained from the synthesis filter bank processing procedure and the sine wave obtained in the sine wave generation processing procedure. Decryption method. A program for causing a computer to execute each processing procedure of the audio decoding method according to claim 3 or 4. A computer-readable recording medium on which a program for causing a computer to execute each processing procedure of the audio decoding method according to claim 3 or 4 is recorded .

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