JP5407832B2 - Speech coding apparatus, speech coding method, speech coding program, speech decoding apparatus, speech decoding method, and speech decoding program - Google Patents

Description

  The present invention relates to a speech encoding apparatus, a speech encoding method, and a speech encoding program that encode a speech signal. The present invention also relates to a speech decoding apparatus, a speech decoding method, and a speech decoding program for decoding a speech signal encoded by the speech encoding apparatus, speech encoding method, and speech encoding program.

  2. Description of the Related Art Conventionally, a technique for performing voice compression based on human auditory characteristics by encoding a voice signal using frequency conversion such as MDCT is well known (for example, see Patent Document 1).

JP-A-2005-128404

  Conventionally, a frequency conversion coefficient obtained by frequency-converting an audio signal is used to identify an unnecessary part in the audio signal on hearing, but is effectively used in terms of reducing redundancy. There is no actual situation.

  The present invention has been made in view of the above circumstances, and provides a speech encoding device, a speech encoding method, and a speech encoding program capable of improving encoding efficiency by predicting a frequency conversion coefficient. The purpose is to do.

  It is another object of the present invention to provide a speech decoding apparatus, speech decoding method, and speech decoding program that can restore a speech signal from the data encoded as described above.

The speech encoding apparatus according to the present invention is
Frequency conversion means for frequency-converting a digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. Adjacent frequency set acquisition means
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition means for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
Predicted value calculation means for calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
Encoding means for encoding coefficient data including at least the prediction value calculated by the prediction value calculation means, and generating encoded coefficient data;
With respect to all the frequency transform coefficients of the frequency transform coefficient group, when the coding coefficient data is generated, the encoded data generating means for generating encoded data that aggregates all the encoded coefficient data,
Each frequency conversion coefficient of the frequency conversion coefficient group is sequentially added to the prediction source data when the process by the predicted value calculation unit is completed.

In addition, a speech encoding apparatus according to another aspect of the present invention includes:
Frequency conversion means for frequency-converting a digital audio signal and calculating a frequency conversion coefficient group;
Logarithmic conversion means for performing logarithmic conversion on the calculated frequency conversion coefficient group and calculating a logarithmic conversion coefficient group;
Obtain logarithmic transformation coefficients to be processed in order from the low-frequency side of the calculated logarithmic transformation coefficient group, and obtain a group of logarithmic transformation coefficients adjacent to the logarithmic transformation coefficient to be processed as a neighboring frequency set. Adjacent frequency set acquisition means
Search for prediction source data in which logarithmic transformation coefficients in the past than the log transformation coefficient to be processed are stored, and obtain a group of logarithmic transformation coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source log transformation coefficient acquisition means for acquiring a log transformation coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source log transformation coefficient;
Predicted value calculation means for calculating a prediction value for deriving the logarithmic conversion coefficient to be processed based on the prediction source logarithmic conversion coefficient;
Encoding means for encoding coefficient data including the prediction value calculated by the prediction value calculation means and a sign of the frequency conversion coefficient corresponding to the logarithmic conversion coefficient to be processed to generate encoded coefficient data; ,
With respect to all logarithmic transform coefficients of the logarithmic transform coefficient group, when the coding coefficient data is generated, the encoded data generation means for generating encoded data that aggregates all the encoded coefficient data, and
Each logarithmic conversion coefficient of the logarithmic conversion coefficient group is sequentially added to the prediction source data when the process by the predicted value calculation unit is completed.

A speech encoding method according to the present invention includes:
A frequency conversion step of frequency-converting the digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. An adjacent frequency set acquisition step,
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition step for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
A predicted value calculation step of calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
An adding step of adding the frequency conversion coefficient for which the processing in the predicted value calculating step has been completed to the prediction source data;
An encoding step of encoding coefficient data including at least the calculated predicted value and generating encoded coefficient data;
An encoded data generation step for generating encoded data that aggregates all the encoded coefficient data when the encoded coefficient data is generated for all frequency converted coefficients of the frequency converted coefficient group; It is characterized by.

The speech encoding program according to the present invention is:
On the computer,
A frequency conversion step of frequency-converting the digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. An adjacent frequency set acquisition step,
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition step for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
A predicted value calculation step of calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
An adding step of adding the frequency conversion coefficient for which the processing in the predicted value calculating step has been completed to the prediction source data;
An encoding step of encoding coefficient data including at least the calculated predicted value and generating encoded coefficient data;
For all frequency transform coefficients of the frequency transform coefficient group, when the coding coefficient data is generated, an encoded data generation step of generating encoded data that aggregates all the encoded coefficient data is executed. It is characterized by that.

The speech decoding apparatus according to the present invention includes:
For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding device for restoring a digital audio signal from encoded data,
Decoding means for reading out and decoding the encoded data from a storage device and restoring the coefficient data;
Adjacent frequency set acquisition means for acquiring a frequency conversion coefficient related to the coefficient data to be processed and a group of frequency conversion coefficients adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient acquisition means for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
Coefficient restoring means for restoring the frequency transform coefficient related to the coefficient data based on the prediction source frequency transform coefficient and the predicted value of the coefficient data;
Frequency inverse transform means for restoring a digital audio signal by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring the frequency transform coefficients related to all coefficient data, and
The restored frequency transform coefficients are sequentially added to the prediction source data.

The speech decoding method according to the present invention includes:
For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding method for restoring a digital audio signal from encoded data,
A decoding step of reading out and decoding the encoded data from a storage device, and restoring each coefficient data;
An adjacent frequency set acquisition step for acquiring a group of frequency conversion coefficients related to the coefficient data to be processed and a frequency conversion coefficient adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient obtaining step for obtaining a frequency transform coefficient adjacent to the obtained prediction source frequency set on the high frequency side as a prediction source frequency transform coefficient;
A coefficient restoration step of restoring the frequency transformation coefficient related to the coefficient data based on the prediction source frequency transformation coefficient and the predicted value of the coefficient data;
An adding step of adding the restored frequency transform coefficient to the prediction source data;
A frequency inverse transform step for restoring a digital audio signal by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring the frequency transform coefficients related to all coefficient data, To do.

A speech decoding program according to the present invention includes:
On the computer,
For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding program for restoring a digital audio signal from encoded data,
A decoding step of reading out and decoding the encoded data from a storage device, and restoring each coefficient data;
An adjacent frequency set acquisition step for acquiring a group of frequency conversion coefficients related to the coefficient data to be processed and a frequency conversion coefficient adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient obtaining step for obtaining a frequency transform coefficient adjacent to the obtained prediction source frequency set on the high frequency side as a prediction source frequency transform coefficient;
A coefficient restoration step of restoring the frequency transformation coefficient related to the coefficient data based on the prediction source frequency transformation coefficient and the predicted value of the coefficient data;
An adding step of adding the restored frequency transform coefficient to the prediction source data;
A frequency inverse transform step for restoring a digital audio signal is performed by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring frequency transform coefficients related to all coefficient data. And

  According to the present invention, encoding efficiency can be improved in audio compression.

It is a block diagram which shows the structure of the audio processing apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the encoding part shown in FIG. It is a figure for demonstrating the search of a prediction source frequency conversion coefficient. 3 is a flowchart illustrating a procedure of encoding processing according to the first embodiment. It is a block diagram which shows the structure of the decoding part shown in FIG. 6 is a flowchart illustrating a procedure of decoding processing according to the first embodiment. It is a block diagram which shows the structure of the encoding part which concerns on Embodiment 2 of this invention. 10 is a flowchart illustrating a procedure of encoding processing according to the second embodiment. It is a block diagram which shows the structure of the decoding part which concerns on Embodiment 2 of this invention. 12 is a flowchart illustrating a procedure of decoding processing according to the second embodiment.

  A speech encoding apparatus and speech decoding apparatus according to embodiments of the present invention will be described below with reference to the drawings. In each of the following embodiments, a case where a speech encoding device and a speech decoding device are applied to a speech processing device will be described.

(Embodiment 1)
As shown in FIG. 1, the voice processing device 1 according to the present embodiment includes a voice input / output device 11, a storage device 12, a ROM 13, a RAM 14, and a CPU 15. These units are connected to each other by a system bus 18. The system bus 18 is a transmission path for transferring commands and data.

  The voice input / output device 11 converts the input voice into a digital signal. The audio input / output device 11 generates a digital audio signal by, for example, sampling the input audio at a sampling frequency of 16 kHz and quantizing the input audio by 16 bits. Further, when a digital audio signal is supplied, the audio input / output device 11 outputs audio corresponding to the digital audio signal.

  The storage device 12 includes, for example, a readable / writable nonvolatile semiconductor memory, a hard disk drive, and the like. The storage device 12 stores a digital audio signal generated by the audio input / output device 11, encoded data (encoded data), and the like, as well as various data necessary for audio processing.

  A ROM (Read Only Memory) 13 stores programs and data necessary for audio processing. A RAM (Random Access Memory) 14 is temporarily used as a work area when the CPU 15 executes sound processing. For example, the RAM 14 stores prediction source data (details will be described later) during audio processing.

  The CPU 15 controls each part of the sound processing apparatus 1 and executes each process described later based on a predetermined program stored in the ROM 13. Functionally, the CPU 15 includes an encoding unit 16 and a decoding unit 17. These are functions realized by the CPU 15 executing a program.

  The encoding unit 16 encodes the digital audio signal converted by the audio input / output device 11. As illustrated in FIG. 2, the encoding unit 16 includes a DC removal unit 161, a frequency conversion unit 162, a coefficient prediction unit 163, an entropy encoding unit 164, and an encoded data generation unit 165.

  The DC removal unit 161 removes a direct current component from the digital audio signal generated by the audio input / output device 11. The reason why the direct current component is removed is that the direct current component is independent of the sound quality. The DC removal unit 161 can be realized by a high-pass filter, for example. The following equation (1) is an example of the transfer function H (z) of the high-pass filter.

  The DC removal unit 161 supplies the digital audio signal from which the direct current component has been removed through the high-pass filter to the frequency conversion unit 162. The frequency conversion unit 162 converts the frequency of the supplied digital audio signal by a predetermined frequency conversion method, and calculates a frequency conversion coefficient group. In the present embodiment, the frequency conversion unit 162 performs frequency conversion by using MDCT (Modified Discrete Cosine Transform). The frequency conversion unit 162 supplies the calculated frequency conversion coefficient group (here, the MDCT coefficient group) to the coefficient prediction unit 163.

  The coefficient prediction unit 163 extracts the frequency conversion coefficients to be processed in order from the low frequency side of the calculated frequency conversion coefficient group, and obtains the frequency conversion coefficient (prediction source frequency conversion coefficient) that is the prediction source of the extracted frequency conversion coefficient. Search from the prediction source data 141. Then, based on the found prediction source frequency conversion coefficient, a prediction value for deriving the frequency conversion coefficient to be processed is obtained. The coefficient prediction unit 163 functions as an adjacent frequency set acquisition unit, a prediction source frequency conversion coefficient acquisition unit, and a prediction value calculation unit. The prediction source data 141 is data composed of past frequency conversion coefficients that have been processed by the coefficient prediction unit 163, and is expanded in the RAM 14 in the present embodiment.

  A method for searching for the prediction source frequency conversion coefficient will be specifically described. The coefficient predicting unit 163 obtains a group (adjacent frequency set) of a predetermined number of processed frequency transform coefficients adjacent to the frequency transform coefficient to be processed on the low frequency side. At this time, if there are no frequency conversion coefficients corresponding to the adjacent frequency set on the low frequency side of the frequency conversion coefficient to be processed, the past frequency conversion coefficients (prediction source data 141) in the same band as the frequency conversion coefficient to be processed Is stored as a prediction source frequency conversion coefficient.

  The coefficient prediction unit 163 searches the prediction source data 141 to find a group (prediction source frequency set) of frequency transform coefficients having the highest correlation (in other words, the most similar) with the adjacent frequency set. The coefficient prediction unit 163 acquires a frequency transform coefficient adjacent to the found prediction source frequency set on the high frequency side (that is, one higher frequency) as a prediction source frequency conversion coefficient (see FIG. 3).

More specifically, the number of frequency transform coefficient groups is n, and the adjacent frequency set to be processed and the frequency transform coefficient groups of the prediction source data 141 are F ₁ = {f _1i | i = 0. 1} and _{F 2 = {f 2i | i} = 0 ... case of the n-1}, the coefficient prediction unit _163, F 1, the _{F 2} distance _{(d (F 1, F 2} )) following the It calculates | requires by Formula (2). Note that the frequency conversion coefficients to be processed are sequentially extracted from the low frequency side of the frequency conversion coefficient group.

The coefficient predicting unit 163 acquires F ₂ having the minimum d (F ₁ , F ₂ ) from the prediction source data 141 as a prediction source frequency set. The coefficient prediction unit 163 acquires a frequency conversion coefficient of one higher frequency of the acquired prediction source frequency set as a prediction source frequency conversion coefficient. The coefficient prediction unit 163 obtains a prediction value for deriving the frequency conversion coefficient to be processed based on the acquired prediction source frequency conversion coefficient. Specifically, the predicted value p when the frequency conversion coefficient to be processed is c _c and the obtained prediction source frequency conversion coefficient is c _p is calculated by the following equation (3).

  In the above formula (3), the smaller absolute value is used as the denominator. This is to prevent noise generation at the time when the audio content is switched.

  The coefficient prediction unit 163 includes a prediction value obtained as described above, and a flag (large / small flag) indicating which of the absolute value of the frequency conversion coefficient to be processed and the absolute value of the prediction source frequency conversion coefficient is large. This is supplied to the entropy encoding unit 164.

  The entropy encoding unit 164 entropy-encodes the coefficient data including the prediction value and the magnitude flag supplied from the coefficient prediction unit 163 to generate encoded coefficient data. Here, since the predicted value is expected to be biased near 0, an improvement in coding efficiency can be expected.

  In addition, the coefficient prediction unit 163 adds the processed frequency conversion coefficient to the prediction source data 141 stored in the RAM 14. In general, digital audio signals before and after the time when the audio content is switched have a low correlation. In such a case, it can be said that the frequency conversion coefficients related to the digital audio signal to be processed are more highly correlated. Therefore, the accuracy of the prediction value (in other words, the search accuracy of the closer prediction source frequency set) can be improved by sequentially adding the frequency conversion coefficients that have been processed to the prediction source data 141.

  When the encoded coefficient data is generated for all frequency conversion coefficients of the frequency conversion coefficient group, the encoded data generation unit 165 generates encoded data in which all the encoded coefficient data are aggregated. The encoded data generation unit 165 stores the generated encoded data in the storage device 12 as part of the audio compression data.

  FIG. 4 is a flowchart showing the procedure of the encoding process executed by the encoding unit 16 described above. This encoding process is started when an operation for starting the audio compression process is performed by the user via an operation input unit (not shown). The operation input unit includes input devices such as a keyboard, a keypad, a touch pad, and a mouse, receives an operation input from the user, and sends the received signal to the CPU 15.

  The DC removal unit 161 acquires the digital audio signal generated by the audio input / output device 11 from the storage device 12 (step S101). The DC removal unit 161 removes a direct current component from the acquired digital audio signal (step S <b> 102) and supplies it to the frequency conversion unit 162. The frequency conversion unit 162 performs frequency conversion (here, MDCT conversion) on the digital audio signal from which the DC component has been removed (step S103), and calculates a frequency conversion coefficient group.

  The coefficient prediction unit 163 extracts the frequency conversion coefficients to be processed in order from the low frequency side of the calculated frequency conversion coefficient group, and further acquires the adjacent frequency set adjacent to the frequency conversion coefficient to be processed on the low frequency side. (Step S104). Then, the coefficient predicting unit 163 searches the prediction source data 141 for a prediction source frequency set that is most similar to the adjacent frequency set, and converts the frequency conversion coefficient adjacent to the found prediction source frequency set on the high frequency side to the prediction source frequency conversion. Obtained as a coefficient (step S105).

  The coefficient prediction unit 163 calculates a prediction value of the frequency conversion coefficient to be processed based on the acquired prediction source frequency conversion coefficient (step S106), and the entropy encoding unit 164 calculates the calculated prediction value and the magnitude flag. To supply. Also, the coefficient prediction unit 163 adds the frequency conversion coefficient for which processing has been completed to the prediction source data 141 (step S107).

  The entropy encoding unit 164 entropy encodes the coefficient data including the prediction value and the magnitude flag supplied from the coefficient prediction unit 163 (step S108), and generates encoded coefficient data. In this way, the processing for one frequency conversion coefficient constituting the frequency conversion coefficient group is completed. When the processing has not been completed for all the frequency conversion coefficients (NO in step S109), the coefficient prediction unit 163 performs the processes of steps S104 to S108 for the frequency conversion coefficient to be processed next.

  On the other hand, when the processing is completed for all the frequency transform coefficients (YES in step S109), the encoded data generation unit 165 generates encoded data in which all the encoded coefficient data is aggregated (step S110) The encoded data is stored in the storage device 12 as a part of the audio compression data related to the audio compression processing.

  The CPU 15 determines whether or not an operation (end operation) for ending the audio compression process has been performed by the user (step S111). When the end operation has not been performed (NO in step S111), the DC removal unit 161 acquires the next digital audio signal generated by the audio input / output device 11 from the storage device 12 (step S101). Subsequent processing is as described above. On the other hand, if an end operation has been performed (YES in step S111), the process (encoding process) and the audio compression process are ended. At that time, the prediction source data 141 stored in the RAM 14 is deleted.

  Next, the decoding unit 17 will be described. The decoding unit 17 restores the digital audio signal from the encoded data generated by the encoding unit 16. As illustrated in FIG. 5, the decoding unit 17 includes an entropy decoding unit 171, a coefficient restoration unit 172, and a frequency inverse transform unit 173.

  The entropy decoding unit 171 reads the encoded data from the audio compression data stored in the storage device 12, performs entropy decoding, and restores each coefficient data (including the predicted value and the magnitude flag).

  For each restored coefficient data, the coefficient restoration unit 172 searches the prediction source data 142 for a frequency conversion coefficient that is a prediction source (prediction source frequency conversion coefficient), finds the found prediction source frequency conversion coefficient, Based on the predicted value of the coefficient data and the magnitude flag, the frequency conversion coefficient is restored. The coefficient restoration unit 172 functions as an adjacent frequency set obtaining unit, a prediction source frequency transform coefficient obtaining unit, and a coefficient restoration unit. The prediction source data 142 is data composed of frequency conversion coefficients that have already been restored by the coefficient restoration unit 172, and is expanded in the RAM 14 in the present embodiment.

  The coefficient restoration unit 172 has a predetermined number of processed frequency transform coefficients (adjacent) adjacent to the frequency transform coefficient corresponding to the coefficient data to be processed (that is, the frequency transform coefficient to be restored) on the low frequency side. Frequency set). At that time, if there are no frequency conversion coefficients corresponding to the adjacent frequency set on the low frequency side, the past frequency conversion coefficients in the same band as the frequency conversion coefficient to be restored, stored in the prediction source data 142, are stored. Predictor frequency conversion coefficient.

  The coefficient restoration unit 172 searches for a group of frequency transform coefficients (prediction source frequency set) having the highest correlation with the adjacent frequency set from the prediction source data 142 using the same method as the coefficient prediction unit 163 of the encoding unit 16 described above. . Then, the frequency transformation coefficient adjacent to the found prediction source frequency set on the high frequency side (that is, one higher frequency region) is acquired as the prediction source frequency transformation coefficient.

  The coefficient restoration unit 172 restores the frequency conversion coefficient corresponding to the coefficient data based on the prediction value, the magnitude flag, and the prediction source frequency conversion coefficient acquired from the prediction source data 142. The coefficient restoration unit 172 supplies the restored frequency transform coefficient to the frequency inverse transform unit 173 and adds it to the prediction source data 142 stored in the RAM 14.

  When the restoration of all the frequency transform coefficients corresponding to the encoded data is completed, the frequency inverse transform unit 173 performs frequency inverse transform (here, IMDCT (Inverse Modified Describe Cosine Transform). : Inversely modified discrete cosine transform))) to restore the digital audio signal. The frequency inverse transform unit 173 stores the restored digital audio signal in the storage device 12.

  FIG. 6 is a flowchart showing the procedure of the decoding process executed by the decoding unit 17 described above. This decoding process is started when the user performs an operation to start the process of expanding the audio compression data stored in the storage device 12 (audio expansion process) via an operation input unit (not shown). The The entropy decoding unit 171 acquires encoded data from the compressed audio data stored in the storage device 12 (step S201), and performs entropy decoding (step S202).

  The coefficient restoration unit 172 performs a process of restoring a corresponding frequency conversion coefficient for each restored coefficient data (predicted value and magnitude flag). First, the coefficient restoration unit 172 searches for a corresponding prediction source frequency conversion coefficient from the prediction source data 142 by the above-described method (step S203). Then, the coefficient restoration unit 172 restores the frequency transform coefficient corresponding to the coefficient data based on the restored predicted value and magnitude flag and the prediction source frequency transform coefficient obtained as a result of the search (step S204). ). The coefficient restoration unit 172 supplies the restored frequency transform coefficient to the frequency inverse transform unit 173 and adds it to the prediction source data 142 (step S205).

  In this way, when the process for one coefficient data is completed, the coefficient restoration unit 172 completes the process for all restored coefficient data (that is, all the frequency transform coefficients corresponding to the encoded data). It is determined whether or not the restoration has been completed (step S206). When the restoration of all the frequency conversion coefficients has not been completed (NO in step S206), the coefficient restoration unit 172 performs a process of restoring the corresponding frequency conversion coefficient for the next coefficient data as described above (steps S203 to S203). S205).

  On the other hand, when the restoration of all the frequency transform coefficients is completed (YES in step S206), the frequency inverse transform unit 173 performs frequency inverse transform (here, IMDCT) on the obtained frequency transform coefficient group. (Step S207), the digital audio signal is restored. The frequency inverse transform unit 173 stores the restored digital audio signal in the storage device 12.

  The CPU 15 determines whether or not the user has performed an operation (end operation) for ending the audio decompression process (step S208). When the end operation has not been performed (NO in step S208), the entropy decoding unit 171 acquires the next encoded data from the audio compression data stored in the storage device 12 (step S201). Subsequent processing is as described above. On the other hand, if an end operation has been performed (YES in step S208), the present process (decoding process) and the audio decompression process are ended. At that time, the prediction source data 142 stored in the RAM 14 is deleted.

  As described above, according to the audio processing device 1 according to the present embodiment of the present invention, a digital audio signal is encoded based on the prediction of the frequency conversion coefficient, and the digital audio signal is encoded from the encoded data. Perform restoration. Therefore, it is possible to improve the encoding efficiency as compared with the conventional case, and to realize audio compression at a lower bit rate. Moreover, since it is not necessary to include the position information of the prediction source in the data to be encoded, the encoding efficiency can be further improved.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described. In the present embodiment, the configurations of the encoding unit 16 and the decoding unit 17 are different from the configurations of the encoding unit 16 and the decoding unit 17 according to the first embodiment.

  As illustrated in FIG. 7, the encoding unit 16 according to the present embodiment includes a DC removal unit 1601, a frequency conversion unit 1602, a logarithmic conversion unit 1603, a coefficient prediction unit 1604, a quantization unit 1605, and entropy encoding. Unit 1606, coefficient restoration unit 1607, and encoded data generation unit 1608.

  The DC removal unit 1601 removes a direct current component from the digital audio signal generated by the audio input / output device 11 by performing the calculation according to the above equation (1), as with the DC removal unit 161 of the first embodiment. Similar to the frequency conversion unit 162 of the first embodiment, the frequency conversion unit 1602 performs frequency conversion on the digital audio signal from which the DC component has been removed using MDCT, and calculates a frequency conversion coefficient group (here, MDCT coefficient group). .

The logarithmic conversion unit 1603 performs logarithmic conversion on the calculated frequency conversion coefficient group to calculate a logarithmic conversion coefficient group. Specifically, the logarithmic transformation unit 1603 calculates the logarithmic transformation coefficient group (C ^L ) from the frequency transformation coefficient group C = {c _i | i = 0... M−1}) based on the following equation (4). = {C ^L _i | i = 0... M−1}).

但し、ｉ＝０...Ｍ−１

However, i = 0 ... M-1

In addition, the logarithmic conversion unit 1603 acquires the code of C (S = {s _i | i = 0... M−1}) (see Expression (5)).

但し、ｉ＝０...Ｍ−１

However, i = 0 ... M-1

  The coefficient prediction unit 1604 extracts logarithmic conversion coefficients to be processed in order from the low frequency side of the calculated logarithmic conversion coefficient group, and calculates logarithmic conversion coefficients (prediction source logarithmic conversion coefficients) that are prediction sources of the extracted logarithmic conversion coefficients. Search from the prediction source data 143. Then, based on the found prediction source log transformation coefficient, a prediction value for deriving the log transformation coefficient to be processed is obtained. The coefficient prediction unit 1604 functions as an adjacent frequency set acquisition unit, a prediction source log transformation coefficient acquisition unit, and a prediction value calculation unit. The prediction source data 143 is data composed of processed logarithmic conversion coefficients, and is expanded in the RAM 14 in this embodiment.

  The search method of the prediction source logarithmic conversion coefficient will be specifically described. The coefficient predicting unit 1604 acquires a predetermined number of processed logarithmic transform coefficient groups (adjacent frequency sets) that are adjacent to the logarithmic transform coefficients to be processed on the low frequency side. At that time, when there are no logarithmic conversion coefficients corresponding to the adjacent frequency set on the low frequency side of the logarithmic conversion coefficient to be processed, the logarithmic conversion coefficient stored in the prediction source data 143 has the same band as the logarithmic conversion coefficient to be processed. The logarithmic conversion coefficient in the past is set as the logarithmic conversion coefficient of the prediction source.

  The coefficient prediction unit 1604 searches the prediction source data 143 to find a group of logarithmic transformation coefficients (prediction source frequency set) having the highest correlation with the adjacent frequency set. The coefficient predicting unit 1604 obtains a logarithmic transformation coefficient adjacent to the found prediction source frequency set on the high frequency side (that is, one higher frequency) as a prediction source log transformation coefficient.

More specifically, the number of logarithmic transform coefficient groups is n, and the adjacent frequency set to be processed and the logarithmic transform coefficient groups of the prediction source data 143 are F ^L ₁ = {f ^L _1i | i = 0. n-1} and _{^{F L 2 = {f L 2i}} | case of the i = 0 ... n-1} , the coefficient prediction unit ^1604, _F L ^1, the distance _{^{F L 2 (d (F L}} 1, F ^L ₂ )) is obtained by the following equation (6). The logarithmic conversion coefficients to be processed are sequentially extracted from the low frequency side of the logarithmic conversion coefficient group.

Coefficient prediction unit ^1604, the ^F _{L 2 where ^{d (F L 1, F L}} 2) is minimized as the prediction based on the frequency set is acquired from the prediction-basis data 143. The coefficient prediction unit 1604 acquires the log transformation coefficient of one higher frequency of the obtained prediction source frequency set as the prediction source log conversion coefficient. The coefficient prediction unit 1604 obtains a prediction value for deriving the logarithmic conversion coefficient to be processed based on the acquired prediction source logarithmic conversion coefficient. Specifically, the predicted value p when the log transformation coefficient to be processed is C ^L _c and the obtained prediction source log transformation coefficient is C ^L _p is calculated by the following equation (7).

  The quantization unit 1605 quantizes the prediction value calculated by the coefficient prediction unit 1604. The entropy encoding unit 1606 entropy-encodes the quantized predicted value and the code of the frequency conversion coefficient corresponding to the logarithmic conversion coefficient to be processed to generate encoded coefficient data.

  The coefficient restoration unit 1607 dequantizes the quantized predicted value to return it to the predicted value, and further restores the logarithmic transformation coefficient using the corresponding prediction source logarithmic transformation coefficient acquired from the prediction source data 143. The coefficient restoration unit 1607 adds the restored logarithmic transformation coefficient to the prediction source data 143 stored in the RAM 14. By sequentially adding the logarithmic transform coefficients that have been processed in this way to the prediction source data 143, the accuracy of the prediction value can be improved as in the encoding unit 16 of the first embodiment.

  When encoded coefficient data is generated for all logarithmic transform coefficients in the logarithmic transform coefficient group, the encoded data generation unit 1608 generates encoded data that aggregates all the encoded coefficient data. The encoded data generation unit 1608 stores the generated encoded data in the storage device 12 as part of the audio compression data.

  FIG. 8 is a flowchart showing the procedure of the encoding process executed by the encoder 16 of the present embodiment described above. This encoding process is started when an operation for starting the audio compression process is performed by the user via an operation input unit (not shown). The operation input unit includes input devices such as a keyboard, a keypad, a touch pad, and a mouse, receives an operation input from the user, and sends the received signal to the CPU 15.

  The DC removal unit 1601 acquires the digital audio signal generated by the audio input / output device 11 from the storage device 12 (step S301). The DC removal unit 1601 removes a direct current component from the acquired digital audio signal (step S302), and supplies it to the frequency conversion unit 1602. The frequency conversion unit 1602 performs frequency conversion (here, MDCT conversion) on the digital audio signal from which the DC component has been removed (step S303), and calculates a frequency conversion coefficient group.

  The logarithmic conversion unit 1603 performs logarithmic conversion on the calculated frequency conversion coefficient group (step S304), and calculates the logarithmic conversion coefficient group. In addition, the logarithmic conversion unit 1603 acquires the sign of each frequency conversion coefficient.

  The coefficient predicting unit 1604 extracts logarithmic conversion coefficients to be processed in order from the low frequency side of the calculated logarithmic conversion coefficient group, and further acquires an adjacent frequency set adjacent to the logarithmic conversion coefficient to be processed on the low frequency side. (Step S305). Then, the coefficient predicting unit 1604 searches the prediction source data 143 for a prediction source frequency set that is most similar to the adjacent frequency set, and predicts a logarithmic transformation coefficient that is adjacent to the found prediction source frequency set on the high frequency side. Obtained as a coefficient (step S306). The coefficient prediction unit 1604 calculates a predicted value of the logarithmic conversion coefficient to be processed based on the acquired predicted logarithmic conversion coefficient (step S307).

  The quantization unit 1605 quantizes the prediction value calculated by the coefficient prediction unit 1604 (step S308). The entropy encoding unit 1606 entropy encodes the quantized predicted value and the code of the corresponding frequency transform coefficient (step S309), and generates encoded coefficient data. The coefficient restoration unit 1607 performs inverse quantization on the quantized prediction value (step S310), returns the prediction value, and further uses the corresponding prediction source logarithmic transformation coefficient acquired from the prediction source data 143 to generate the prediction value. Restore logarithmic transformation coefficients from. Then, the restored logarithmic transformation coefficient is added to the prediction source data 143 (step S311).

  In this way, the process for one logarithmic transformation coefficient constituting the logarithmic transformation coefficient group is completed. When the process has not been completed for all logarithmic conversion coefficients (NO in step S312), the coefficient prediction unit 1604 performs the processes of steps S305 to S311 for the logarithmic conversion coefficient to be processed next.

  On the other hand, when the processing has been completed for all logarithmic transform coefficients (YES in step S312), the encoded data generation unit 1608 generates encoded data in which all the encoded coefficient data are aggregated (step S313). The encoded data is stored in the storage device 12 as a part of the audio compression data related to the audio compression processing.

  The CPU 15 determines whether or not an operation (end operation) for ending the audio compression process has been performed by the user (step S314). If the end operation has not been performed (NO in step S314), the DC removal unit 1601 acquires the next digital audio signal generated by the audio input / output device 11 from the storage device 12 (step S301). Subsequent processing is as described above. On the other hand, if an end operation has been performed (YES in step S314), the process (encoding process) and the audio compression process are ended. At this time, the prediction source data 143 stored in the RAM 14 is deleted.

  Next, the decoding unit 17 of this embodiment will be described. As illustrated in FIG. 9, the decoding unit 17 includes an entropy decoding unit 1701, an inverse quantization unit 1702, a coefficient restoration unit 1703, a linear conversion unit 1704, and a frequency inverse conversion unit 1705.

  The entropy decoding unit 1701 reads the encoded data from the compressed audio data stored in the storage device 12, performs entropy decoding, and includes each coefficient data (quantized prediction value and code of the corresponding frequency transform coefficient). .) To restore. The inverse quantization unit 1702 restores the predicted value by inversely quantizing the quantized predicted value for each restored coefficient data.

  For each restored coefficient data, the coefficient restoration unit 1703 searches the prediction source data 144 for a logarithmic conversion coefficient (prediction source logarithmic conversion coefficient) that is a prediction source, finds the found prediction source logarithmic conversion coefficient, The logarithmic conversion coefficient is restored based on the predicted value of the coefficient data. The prediction source data 144 is data composed of logarithmic transformation coefficients that have already been restored by the coefficient restoration unit 1703, and is expanded in the RAM 14 in this embodiment.

  The coefficient restoration unit 1703 has a predetermined number of processed logarithmic transformation coefficients (adjacent to the logarithmic transformation coefficients corresponding to the coefficient data to be processed (that is, logarithmic transformation coefficients to be restored) adjacent on the low frequency side. Frequency set). At this time, if there are no logarithmic conversion coefficients corresponding to the adjacent frequency set on the low frequency side, the past logarithmic conversion coefficients stored in the prediction source data 144 and in the same band as the logarithmic conversion coefficient to be restored are stored. Predictor logarithmic conversion coefficient.

  The coefficient restoration unit 1703 searches the prediction source data 144 for a group of logarithmic transform coefficients (prediction source frequency set) having the highest correlation with the adjacent frequency set using the same method as the coefficient prediction unit 1604 of the encoding unit 16 described above. . Then, a logarithmic transformation coefficient adjacent to the found prediction source frequency set on the high frequency side (that is, one high frequency region) is acquired as a prediction source log transformation coefficient.

  The coefficient restoration unit 1703 restores a logarithmic transformation coefficient corresponding to the coefficient data based on the prediction value and the prediction source log transformation coefficient acquired from the prediction source data 144. The coefficient restoration unit 1703 supplies the restored logarithmic transformation coefficient and the code of the corresponding frequency transformation coefficient to the linear transformation unit 1704 and adds the restored logarithmic transformation coefficient to the prediction source data 144 stored in the RAM 14.

  The linear transformation unit 1704 restores the frequency transformation coefficient by performing transformation from the logarithmic axis to the linear axis with respect to the logarithmic transformation coefficient supplied from the coefficient restoration unit 1703.

  When the restoration of all the frequency transform coefficients corresponding to the encoded data is completed, the frequency inverse transform unit 1705 performs frequency inverse transform (here, IMDCT) on the obtained frequency transform coefficient group, and performs digital conversion. Restore the audio signal. The frequency inverse transform unit 1705 stores the restored digital audio signal in the storage device 12.

  FIG. 10 is a flowchart showing the procedure of the decoding process executed by the decoding unit 17 of this embodiment described above. This decoding process is started when the user performs an operation to start the process of expanding the audio compression data stored in the storage device 12 (audio expansion process) via an operation input unit (not shown). The The entropy decoding unit 1701 acquires encoded data from the audio compression data stored in the storage device 12 (step S401), and performs entropy decoding (step S402).

  When each coefficient data (including the quantized prediction value and the code of the corresponding frequency transform coefficient) is restored by the entropy decoding unit 1701, the inverse quantization unit 1702, the coefficient restoration unit 1703, and the linear transformation unit 1704 are restored. Performs the following processing for each restored coefficient data.

  First, the inverse quantization unit 1702 performs inverse quantization on the quantized predicted value (step S403) to restore the predicted value. The coefficient restoration unit 1703 searches for the corresponding prediction source logarithmic conversion coefficient from the prediction source data 144 by the method described above (step S404). Then, the coefficient restoration unit 1703 restores a logarithmic transformation coefficient corresponding to the coefficient data based on the predicted value and the prediction source log transformation coefficient extracted from the prediction source data 144 (step S405). The coefficient restoration unit 1703 supplies the restored logarithmic transformation coefficient and the code of the corresponding frequency transformation coefficient to the linear transformation unit 1704, and adds the restored logarithmic transformation coefficient to the prediction source data 144 (step S406).

  The linear transformation unit 1704 restores the frequency transformation coefficient by performing transformation from the logarithmic axis to the linear axis with respect to the logarithmic transformation coefficient supplied from the coefficient restoration unit 1703 (step S407).

  When the process for one coefficient data is completed in this way, the inverse quantization unit 1702 has completed the process for all the restored coefficient data (that is, all the frequency transform coefficients corresponding to the encoded data). It is determined whether or not the restoration has been completed (step S408). When the restoration of all the frequency transform coefficients has not been completed (NO in step S408), the inverse quantization unit 1702, the coefficient restoration unit 1703, and the linear transformation unit 1704 perform the same process as described above for the next coefficient data ( Steps S403 to S407).

  On the other hand, when the restoration of all the frequency transform coefficients is completed (YES in step S408), the frequency inverse transform unit 1705 performs frequency inverse transform (here, IMDCT) on the obtained frequency transform coefficient group. (Step S409), the digital audio signal is restored. The frequency inverse transform unit 1705 stores the restored digital audio signal in the storage device 12.

  The CPU 15 determines whether or not the user has performed an operation (end operation) for ending the audio decompression process (step S410). If the end operation has not been performed (NO in step S410), the entropy decoding unit 1701 acquires the next encoded data from the audio compression data stored in the storage device 12 (step S401). Subsequent processing is as described above. On the other hand, if an end operation has been performed (YES in step S410), the present process (decoding process) and the audio decompression process are ended. At that time, the prediction source data 144 stored in the RAM 14 is deleted.

  As described above, according to the audio processing device 1 according to the present embodiment of the present invention, a digital audio signal is encoded based on the prediction of the frequency conversion coefficient, and the digital audio signal is encoded from the encoded data. Perform restoration. Therefore, it is possible to improve the encoding efficiency as compared with the conventional case, and to realize audio compression at a lower bit rate. Moreover, since it is not necessary to include the position information of the prediction source in the data to be encoded, the encoding efficiency can be further improved.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  For example, in each of the above embodiments, MDCT is used as the frequency conversion. However, the frequency conversion is not limited to MDCT, and DCT (Descrete Cosine Transform) or DFT (Discrete Fourier Transform). It may be.

  In each of the above embodiments, the functions of the encoding unit 16 and the decoding unit 17 described above are realized by logical processing by the CPU 15 executing a program. For example, ASIC (Application Specific Integrated) The above-described functions may be realized by hardware such as Circuit).

  Furthermore, an existing personal computer (PC) or the like can be caused to function as a speech encoding device or speech decoding device according to the present invention. That is, the program as executed by the CPU 15 described above is applied to an existing PC or the like, and the CPU or the like of the PC or the like executes the program so that the PC or the like can be used as the speech encoding apparatus or the speech according to the present invention. It becomes possible to function as a decoding device.

  Such a program distribution method is arbitrary, for example, a computer-readable recording medium such as a CD-ROM (Compact Disk Read-Only Memory), a DVD (Digital Versatile Disk), an MO (Magneto Optical Disk), or a memory card. It may be stored and distributed in a network, or distributed via a communication network such as the Internet.

  In this case, when the functions according to the present invention described above are realized by sharing an OS (operating system) and an application program, or by cooperation between the OS and the application program, only the application program portion is stored in a recording medium or the like. May be.

  DESCRIPTION OF SYMBOLS 1 ... Voice processing apparatus, 11 ... Voice input / output device, 12 ... Memory | storage device, 13 ... ROM, 14 ... RAM, 15 ... CPU, 16 ... Encoding part, 17 ... Decoding part, 18 ... System bus, 141-144 ... Prediction source data, 161, 1601 ... DC removal unit, 162, 1602 ... frequency conversion unit, 163,1604 ... coefficient prediction unit, 164,1606 ... entropy encoding unit, 165,1608 ... encoded data generation unit, ... entropy decoding unit, 172, 1607, 1703 ... coefficient restoration unit, 173, 1705 ... frequency inverse transformation unit, 1603 ... logarithmic transformation unit, 1605 ... quantization unit, 1702 ... inverse quantization unit, 1704 ... linear transformation unit

Claims (9)

Frequency conversion means for frequency-converting a digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. Adjacent frequency set acquisition means
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition means for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
Predicted value calculation means for calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
Encoding means for encoding coefficient data including at least the prediction value calculated by the prediction value calculation means, and generating encoded coefficient data;
With respect to all the frequency transform coefficients of the frequency transform coefficient group, when the coding coefficient data is generated, the encoded data generating means for generating encoded data that aggregates all the encoded coefficient data,
Each frequency conversion coefficient of the frequency conversion coefficient group is sequentially added to the prediction source data when the process by the predicted value calculation unit is completed.
A speech encoding apparatus characterized by that. The predicted value calculation means calculates the predicted value by division using either the frequency conversion coefficient to be processed or the prediction source frequency conversion coefficient as a denominator and the other as a numerator,
The speech coding apparatus according to claim 1. The coefficient data encoded by the encoding means further includes a flag indicating which of the absolute value of the frequency conversion coefficient to be processed and the absolute value of the prediction source frequency conversion coefficient is larger,
The predicted value calculation means uses the smaller one of the absolute value of the frequency conversion coefficient to be processed and the absolute value of the prediction source frequency conversion coefficient as the denominator during the division.
The speech encoding apparatus according to claim 2. Frequency conversion means for frequency-converting a digital audio signal and calculating a frequency conversion coefficient group;
Logarithmic conversion means for performing logarithmic conversion on the calculated frequency conversion coefficient group and calculating a logarithmic conversion coefficient group;
Obtain logarithmic transformation coefficients to be processed in order from the low-frequency side of the calculated logarithmic transformation coefficient group, and obtain a group of logarithmic transformation coefficients adjacent to the logarithmic transformation coefficient to be processed as a neighboring frequency set. Adjacent frequency set acquisition means
Search for prediction source data in which logarithmic transformation coefficients in the past than the log transformation coefficient to be processed are stored, and obtain a group of logarithmic transformation coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source log transformation coefficient acquisition means for acquiring a log transformation coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source log transformation coefficient;
Predicted value calculation means for calculating a prediction value for deriving the logarithmic conversion coefficient to be processed based on the prediction source logarithmic conversion coefficient;
Encoding means for encoding coefficient data including the prediction value calculated by the prediction value calculation means and a sign of the frequency conversion coefficient corresponding to the logarithmic conversion coefficient to be processed to generate encoded coefficient data; ,
With respect to all logarithmic transform coefficients of the logarithmic transform coefficient group, when the coding coefficient data is generated, the encoded data generation means for generating encoded data that aggregates all the encoded coefficient data, and
Each logarithmic conversion coefficient of the logarithmic conversion coefficient group is sequentially added to the prediction source data when the process by the predicted value calculation unit is completed.
A speech encoding apparatus characterized by that. A frequency conversion step of frequency-converting the digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. An adjacent frequency set acquisition step,
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition step for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
A predicted value calculation step of calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
An adding step of adding the frequency conversion coefficient for which the processing in the predicted value calculating step has been completed to the prediction source data;
An encoding step of encoding coefficient data including at least the calculated predicted value and generating encoded coefficient data;
For all frequency transform coefficients of the frequency transform coefficient group, when the coding coefficient data is generated, an encoded data generation step of generating encoded data that aggregates all the encoded coefficient data, and
A speech encoding method characterized by the above. On the computer,
A frequency conversion step of frequency-converting the digital audio signal and calculating a frequency conversion coefficient group;
The frequency conversion coefficients to be processed are acquired in order from the low frequency side of the calculated frequency conversion coefficient group, and a group of frequency conversion coefficients adjacent to the processing target frequency conversion coefficient on the low frequency side is acquired as an adjacent frequency set. An adjacent frequency set acquisition step,
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficient to be processed are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set, A prediction source frequency conversion coefficient acquisition step for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
A predicted value calculation step of calculating a predicted value for deriving the frequency conversion coefficient to be processed based on the prediction source frequency conversion coefficient;
An adding step of adding the frequency conversion coefficient for which the processing in the predicted value calculating step has been completed to the prediction source data;
An encoding step of encoding coefficient data including at least the calculated predicted value and generating encoded coefficient data;
For all frequency transform coefficients of the frequency transform coefficient group, when the coding coefficient data is generated, an encoded data generation step of generating encoded data that aggregates all the encoded coefficient data is executed.
A speech encoding program characterized by the above. For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding device for restoring a digital audio signal from encoded data,
Decoding means for reading out and decoding the encoded data from a storage device and restoring the coefficient data;
Adjacent frequency set acquisition means for acquiring a frequency conversion coefficient related to the coefficient data to be processed and a group of frequency conversion coefficients adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient acquisition means for acquiring a frequency conversion coefficient adjacent to the acquired prediction source frequency set on the high frequency side as a prediction source frequency conversion coefficient;
Coefficient restoring means for restoring the frequency transform coefficient related to the coefficient data based on the prediction source frequency transform coefficient and the predicted value of the coefficient data;
Frequency inverse transform means for restoring a digital audio signal by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring the frequency transform coefficients related to all coefficient data, and
The restored frequency transform coefficient is sequentially added to the prediction source data.
A speech decoding apparatus characterized by that. For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding method for restoring a digital audio signal from encoded data,
A decoding step of reading out and decoding the encoded data from a storage device, and restoring each coefficient data;
An adjacent frequency set acquisition step for acquiring a group of frequency conversion coefficients related to the coefficient data to be processed and a frequency conversion coefficient adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient obtaining step for obtaining a frequency transform coefficient adjacent to the obtained prediction source frequency set on the high frequency side as a prediction source frequency transform coefficient;
A coefficient restoration step of restoring the frequency transformation coefficient related to the coefficient data based on the prediction source frequency transformation coefficient and the predicted value of the coefficient data;
An adding step of adding the restored frequency transform coefficient to the prediction source data;
A frequency inverse transform step for restoring the digital audio signal by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring the frequency transform coefficients related to all coefficient data,
A speech decoding method characterized by the above. On the computer,
For each frequency conversion coefficient of the frequency conversion coefficient group corresponding to the digital audio signal, encoded coefficient data obtained by encoding coefficient data including at least a prediction value for deriving the frequency conversion coefficient from the past frequency conversion coefficient is stored. An audio decoding program for restoring a digital audio signal from encoded data,
A decoding step of reading out and decoding the encoded data from a storage device, and restoring each coefficient data;
An adjacent frequency set acquisition step for acquiring a group of frequency conversion coefficients related to the coefficient data to be processed and a frequency conversion coefficient adjacent on the low frequency side as an adjacent frequency set;
Search for prediction source data in which frequency conversion coefficients in the past than the frequency conversion coefficients related to the coefficient data are stored, and obtain a group of frequency conversion coefficients having the highest correlation with the adjacent frequency set as a prediction source frequency set. A prediction source frequency transform coefficient obtaining step for obtaining a frequency transform coefficient adjacent to the obtained prediction source frequency set on the high frequency side as a prediction source frequency transform coefficient;
A coefficient restoration step of restoring the frequency transformation coefficient related to the coefficient data based on the prediction source frequency transformation coefficient and the predicted value of the coefficient data;
An adding step of adding the restored frequency transform coefficient to the prediction source data;
Performing a frequency inverse transform step for restoring a digital audio signal by performing frequency inverse transform on the frequency transform coefficient group obtained by restoring the frequency transform coefficients related to all coefficient data,
A speech decoding program characterized by the above.

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