JP6256293B2 - Digital audio processing apparatus, digital audio processing method, digital audio processing program - Google Patents

Description

  The present invention relates to a digital audio processing apparatus, a digital audio processing method, and a digital audio processing program for processing a digital audio signal.

  In recent years, high-resolution digital audio signals (hereinafter referred to as HR audio signals) with higher sound quality than digital audio signals (hereinafter referred to as CD audio signals) recorded on compact discs (CDs) have appeared and attracted attention.

  The CD audio signal is a signal obtained by converting an analog audio signal into a digital audio signal with a quantization bit number of 16 bits and a sampling frequency of 44.1 kHz. In a CD audio signal, the frequency band is limited to 22.05 kHz.

  On the other hand, the HR audio signal has a larger number of quantization bits than that in CD or a sampling frequency higher than that in CD. For example, if the number of quantization bits is 24 bits and the sampling frequency is 176.4 kHz, the frequency band is 88.2 kHz. Therefore, the HR audio signal can reproduce minute changes in sound that cannot be reproduced by the CD audio signal, and has higher sound quality than the CD audio signal.

  However, music studios often have only a master sound source of a format called a CD master, which has a quantization bit number of 16 bits and a sampling frequency of 44.1 kHz. Therefore, the CD audio signal of the CD master is converted into an HR audio signal by converting the number of bits and sampling frequency.

Japanese Patent No. 3401171 Japanese Patent No. 3659489

  Patent Documents 1 and 2 describe a technique for improving sound quality that improves sound quality on hearing when a digital audio signal is reproduced. It can be considered that the digital sound signal obtained by converting the CD sound signal into the HR sound signal is subjected to the signal processing of the digital sound processing device described in Patent Documents 1 and 2 to improve the sound quality.

  However, when the HR audio signal is processed by the digital audio processing apparatus described in Patent Documents 1 and 2, the balance of the sound is biased toward the high frequency, and the balance of the low frequency, mid frequency, and high frequency is lost. It may take.

  The present invention provides a second digital signal having a second sampling frequency higher than the first sampling frequency by converting the first digital audio signal having the first sampling frequency in a balanced manner in the low frequency, mid frequency, and high frequency. It is an object of the present invention to provide a digital audio processing device, a digital audio processing method, and a digital audio processing program that can improve the sound quality of a digital audio signal converted into an audio signal.

  In order to solve the above-described problems of the related art, the present invention converts a first digital audio signal having a first sampling frequency into a second digital having a second sampling frequency higher than the first sampling frequency. A digital audio signal converted into an audio signal is used as a digital audio signal to be processed, and a waveform is corrected by the first waveform correction processing unit that corrects the waveform of the digital audio signal to be processed, and the first waveform correction processing unit. A second waveform correction processing unit that corrects a waveform of the digital audio signal to be processed, and the first waveform correction processing unit includes, among sample data constituting the digital audio signal to be processed, Sample data is extracted at the sample interval of the first digital audio signal, and based on the extracted sample data, the maximum sample data and the maximum data are extracted. A first extreme value calculation unit that calculates sample data of a value, a first sample number detection unit that detects the number of samples between adjacent maximum value sample data and minimum value sample data, and the processing A first difference value calculation unit that calculates a difference value between adjacent sample data in the sample data constituting the target digital audio signal, and a predetermined coefficient for the difference value calculated by the first difference value calculation unit A first correction value calculation unit that calculates a correction value by multiplication, and a sample of a maximum value calculated by at least the first extreme value calculation unit among sample data constituting the digital audio signal to be processed The sample data immediately before and after the data adjacent to the data and the sample data before and after the maximum sample data at the sample interval of the first digital audio signal The correction value calculated by the first correction value calculation unit is added to each sample data included between the sample data and at least a sample of the minimum value calculated by the first extreme value calculation unit Between the previous and next sample data adjacent to the data and the previous and next sample data adjacent to the minimum sample data at the sample interval of the first digital audio signal A first addition / subtraction unit that subtracts the correction value calculated by the first correction value calculation unit from each of the included sample data, and the second waveform correction processing unit includes the first waveform Second extreme for calculating maximum value sample data and minimum value sample data based on sample data constituting the digital audio signal to be processed output from the correction processing unit A value calculation unit, a second sample number detection unit that detects the number of samples between adjacent maximum value sample data and minimum value sample data, and adjacent sample data constituting the digital audio signal to be processed A second difference value calculation unit that calculates a difference value between sample data to be calculated, and a second correction that calculates a correction value by multiplying the difference value calculated by the second difference value calculation unit by a predetermined coefficient Among the sample data constituting the value calculation unit and the digital audio signal to be processed, at least one sample before and one sample adjacent to the sample data of the maximum value calculated by the second extreme value calculation unit The correction value calculated by the second correction value calculation unit is added to the sample data, and at least adjacent to the sample data of the minimum value calculated by the second extreme value calculation unit And a second addition / subtraction unit that subtracts the correction value calculated by the second correction value calculation unit from the previous and next sample data. .

  In order to solve the above-described problems of the related art, the present invention converts a first digital audio signal having a first sampling frequency into a second sampling frequency that is higher than the first sampling frequency. The digital audio signal converted into the digital audio signal is used as a digital audio signal to be processed, and sample data is extracted from the sample data constituting the digital audio signal to be processed at the sample interval of the first digital audio signal. An extraction step, a first extreme value calculation step for calculating the sample data of the maximum value and the sample data of the minimum value based on the sample data extracted in the extraction step, the sample data and the minimum value of the adjacent maximum value A first sample number detecting step for detecting the number of samples between the sample data and the processing data; A first difference value calculating step for calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal, and multiplying the difference value calculated in the first difference value calculating step by a predetermined coefficient A first correction value calculating step for calculating a correction value, and among the sample data constituting the digital audio signal to be processed, at least the sample data of the maximum value calculated in the first extreme value calculating step Between the sample data immediately before and after the sample data adjacent to the sample data and the sample data before and after the sample data adjacent to the maximum sample data at the sample interval of the first digital audio signal. The correction value calculated in the first correction value calculation step is added to each sample data to be calculated, and at least calculated in the first extreme value calculation step. One sample data before and after the sample data of the minimum value, and one sample data before and after the sample data of the minimum value at the sample interval of the first digital audio signal. The first addition / subtraction step for subtracting the correction value calculated in the first correction value calculation step and the addition / subtraction processing in the first addition / subtraction step from each sample data included between the sample data A second extreme value calculating step for calculating local maximum sample data and local minimum sample data based on the sample data constituting the digital audio signal to be processed; and adjacent local maximum sample data and local minimum value A second sample number detecting step for detecting the number of samples between the sample data and the sample data constituting the digital audio signal to be processed; A correction value is calculated by multiplying a difference value calculated in the second difference value calculation step for calculating a difference value between adjacent sample data in the data by the second difference value calculation step by a predetermined coefficient. Of the sample data constituting the second correction value calculating step and the digital audio signal to be processed, at least one sample data adjacent to the maximum value sample data calculated in the second extreme value calculation step and The correction value calculated in the second correction value calculation step is added to the next sample data, and at least one sample data adjacent to the minimum value sample data calculated in the second extreme value calculation step. And a second adding / subtracting step for subtracting the correction value calculated in the second correction value calculating step from the previous and next sample data. The law provides.

  Furthermore, in order to solve the above-described problems of the related art, the present invention converts a first digital audio signal having a first sampling frequency into a second sampling frequency that is higher than the first sampling frequency. The digital audio signal converted into the digital audio signal is used as a digital audio signal to be processed, and the sample data among the sample data constituting the digital audio signal to be processed is sampled at a sample interval of the first digital audio signal. A first extreme value calculating step for calculating the maximum value sample data and the minimum value sample data based on the sample data extracted in the extraction step, and the adjacent maximum value sample data A first sample number detection step for detecting the number of samples between the sample data and the minimum sample data. And a first difference value calculating step for calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed, and a difference value calculated in the first difference value calculating step Among the sample data constituting the digital audio signal to be processed, and at least the first extreme value calculating step. One sample data before and after the sample data adjacent to the maximum sample data, and one sample before and one sample next to the sample data of the maximum value at the sample interval of the first digital audio signal The correction value calculated in the first correction value calculation step is added to each sample data included between the data and at least the first pole The sample data immediately before and after adjacent to the sample data of the minimum value calculated in the calculation step, and the one before and adjacent to the sample data of the minimum value at the sample interval of the first digital audio signal A first addition / subtraction step for subtracting the correction value calculated in the first correction value calculation step from each sample data included between the next sample data and the addition / subtraction in the first addition / subtraction step A second extreme value calculating step for calculating a maximum value sample data and a minimum value sample data based on the sample data constituting the processed digital audio signal to be processed; and adjacent maximum value sample data A second sample number detection step for detecting the number of samples between the sample data and the minimum sample data, and the digital audio signal to be processed A second difference value calculating step for calculating a difference value between adjacent sample data in the sample data to constitute, and a correction value by multiplying the difference value calculated in the second difference value calculating step by a predetermined coefficient Of the sample data constituting the second correction value calculation step to be calculated and the digital audio signal to be processed, at least one sample data adjacent to the sample data of the maximum value calculated in the second extreme value calculation step The correction value calculated in the second correction value calculation step is added to the previous and next sample data, and at least adjacent to the minimum value sample data calculated in the second extreme value calculation step And a second addition / subtraction step for subtracting the correction value calculated in the second correction value calculation step from the previous and next sample data. It provides digital sound processing program to.

  According to the digital audio processing device, the digital audio processing method, and the digital audio processing program of the present invention, the first digital audio signal having the first sampling frequency and the first digital audio signal in a balanced manner in the low frequency, mid frequency, and high frequency is The sound quality of the digital audio signal converted into the second digital audio signal having the second sampling frequency higher than the sampling frequency can be improved.

It is a block diagram which shows the whole structure of the digital audio processing apparatus of one Embodiment. It is a block diagram which shows the specific structural example of the waveform correction process part 1 in FIG. It is a block diagram which shows the specific structural example of the waveform correction process part 2 in FIG. It is a wave form diagram showing an example of sample data which constitutes a high resolution digital audio signal processed with a digital audio processing device of one embodiment, a digital audio processing method, and a digital audio processing program. It is a figure which shows the example of the table of the correction value set for every sample space | interval between maximum value and minimum value. It is a figure for demonstrating the fundamental view of the sample data of the maximum value vicinity or minimum value vicinity which the addition / subtraction part in FIG.2, FIG.3 adds / subtracts a correction value. It is a figure for demonstrating the fundamental view of the sample data of the maximum value vicinity or minimum value vicinity which the addition / subtraction part in FIG.2, FIG.3 adds / subtracts a correction value. FIG. 3 is a waveform diagram showing a state where correction values are added by the waveform correction processing unit 1 shown in FIG. 2. FIG. 4 is a waveform diagram showing a state where correction values are added by the waveform correction processing unit 2 shown in FIG. 3. FIG. 4 is a waveform diagram showing a state in which correction values are added and subtracted by the waveform correction processing unit 1 shown in FIG. 2 and the waveform correction processing unit 2 shown in FIG. 3. It is a block diagram which shows the structural example of the microcomputer which executes the digital audio processing program of one Embodiment. It is a flowchart which shows the process which the digital audio processing program of one Embodiment performs a microcomputer.

  Hereinafter, a digital audio processing apparatus, a digital audio processing method, and a digital audio processing program according to an embodiment will be described with reference to the accompanying drawings.

  In the present embodiment, a digital audio signal obtained by converting a first digital audio signal having a first sampling frequency into a second digital audio signal having a second sampling frequency higher than the first sampling frequency is processed. The target digital audio signal is used.

  The first digital audio signal is, for example, a CD audio signal, and the second digital audio signal is, for example, an HR audio signal. In the present embodiment, the HR audio signal is a digital audio signal obtained by converting a CD audio signal having a quantization bit number of 16 bits and a sampling frequency of 44.1 kHz into a quantization bit number of 24 bits and a sampling frequency of 176.4 kHz. Take an example.

  The first digital audio signal and the second digital audio signal are not limited to the above example. It may be a digital audio signal obtained by converting an audio signal having a quantization bit number of 16 bits and a sampling frequency of 48 kHz into a quantization bit number of 24 bits and a sampling frequency of 192 kHz. It may be a digital audio signal obtained by converting an audio signal having a quantization bit number of 24 bits and a sampling frequency of 96 kHz into a quantization bit number of 24 bits and a sampling frequency of 192 kHz.

  In FIG. 1, an HR audio signal is input to a waveform correction processing unit 1 and subjected to waveform correction processing described later. The HR audio signal output from the waveform correction processing unit 1 is input to the waveform correction processing unit 2 and subjected to waveform correction processing described later and output.

  Here, the HR audio signal input to the waveform correction processing unit 1 is an audio signal obtained by converting an audio signal having a sampling frequency lower than that of the HR audio signal input to the waveform correction processing unit 1 into a sampling frequency of the HR audio signal. .

  As shown in FIG. 2, the waveform correction processing unit 1 includes an extreme value calculation unit 11, a sample number detection unit 12, a difference value calculation unit 13, a correction value calculation unit 14, and an addition / subtraction unit 15. As shown in FIG. 3, the waveform correction processing unit 2 includes an extreme value calculation unit 21, a sample number detection unit 22, a difference value calculation unit 23, a correction value calculation unit 24, and an addition / subtraction unit 25.

  Each unit constituting the waveform correction processing units 1 and 2 may be configured by hardware or may be configured by software. Hardware and software may be mixed. Each unit constituting the waveform correction processing units 1 and 2 may be configured by an integrated circuit, or each of the waveform correction processing units 1 and 2 may be configured by an integrated circuit.

  First, the operation of the waveform correction processing unit 1 shown in FIG. 2 will be described with reference to FIGS.

  FIG. 4 shows an example of the waveform of sample data constituting the HR audio signal. FIG. 4 shows only a portion where the sample value increases with time. As shown in FIG. 4, the HR audio signal includes sample data S0 to S8.

  Sample data S0, S4, and S8 are sample data originally possessed by the CD audio signal. Sample data S1 to S3 and S5 to S7 are sample data added by multiplying the sampling frequency of the CD audio signal by four.

  The extreme value calculation unit 11 extracts sample data at the sample interval T0 of the CD audio signal from the sample data of the input HR audio signal, and determines the maximum value and the minimum value by determining the size relationship between adjacent sample data. Value.

  Here, since the HR audio signal is a digital audio signal obtained by quadrupling the sampling frequency of the CD audio signal, the extreme value calculation unit 11 may extract sample data every 4 sample data.

  The second digital sound having a second sampling frequency in which the HR sound signal is a first digital sound signal having the first sampling frequency and is N times the first sampling frequency (N is a natural number of 2 or more). It is assumed that the digital audio signal is converted into a signal. At this time, the extreme value calculation unit 11 may extract sample data for each N sample data.

  In the case of FIG. 4, the extreme value calculation unit 11 calculates that the sample data S0 is a minimum value and the sample data S8 is a maximum value.

  The sample number detection unit 12 detects the number of samples (sample interval) between the maximum value and the minimum value. The number of samples between the maximum value and the minimum value is the number of samples where the sample value increases from the minimum value to the maximum value as shown in FIG. 4, and the sample value decreases from the maximum value to the minimum value. This means the number of samples in the part to be processed.

  The number of samples detected by the sample number detection unit 12 is the number of samples at the sample interval T0 of the CD audio signal extracted by the extreme value calculation unit 11. Therefore, in the case of FIG. 4, the sample number detection unit 12 detects that the interval is two samples.

  The difference value calculation unit 13 receives the detection result from the sample number detection unit 12 and the HR audio signal. The difference value calculation unit 13 calculates a difference value between adjacent sample data in the HR audio signal. The adjacent sample data here is adjacent sample data at the sample interval T1 of the HR audio signal.

  The correction value calculation unit 14 calculates a correction value by multiplying a difference value between adjacent sample data by a predetermined coefficient. The coefficient is a number less than one. A coefficient corresponding to the number of samples is set in the correction value calculation unit 14. The correction value calculation unit 14 selects a coefficient according to the number of samples detected by the sample number detection unit 12.

  It is preferable that a level selection signal is input to the correction value calculation unit 14, and the correction value can be adjusted by selecting a coefficient by which the difference value is multiplied by the level selection signal.

  The addition / subtraction unit 15 adds the correction value to the sample data near the maximum value, and subtracts the correction value from the sample data near the minimum value. In addition, the addition / subtraction unit 15 may add the correction value to the sample data of the maximum value and subtract the correction value from the sample data of the minimum value. The meaning of the neighborhood will be described later.

  Here, an example of a coefficient by which the correction value calculation unit 14 multiplies the difference value between adjacent sample data will be described with reference to FIG. As shown in FIG. 5, the correction value calculation unit 14 has coefficients corresponding to the level selection signals 00, 01, 10, and 11 in the interval between the maximum value and the minimum value from 2 samples to a predetermined number of samples. Is set. The predetermined number may be set as appropriate.

  In FIG. 4, assuming that the CD audio signal has an interval of 2 samples and the level selection signal is 00, the correction value calculation unit 14 calculates a correction value by multiplying the difference value between adjacent sample data by a coefficient 1/2. And

  The basic concept of sample data in the vicinity of the maximum value or the vicinity of the minimum value to which the addition / subtraction unit 15 adds / subtracts the correction value will be described with reference to FIGS. 6 and 7. This basic concept is similarly applied to addition / subtraction processing in the addition / subtraction unit 25 in FIG.

  In FIGS. 6 and 7, Smax is sample data with a maximum value, and Smin is sample data with a minimum value. S (-1) and S (-2) are the sample data one and two before the maximum or minimum sample data, and S (+1) and S (+2) are the maximum or minimum This is sample data after one and two samples of value sample data.

  As an example, the addition / subtraction unit 15 performs addition / subtraction processing illustrated in FIGS. 6A and 6B and addition / subtraction illustrated in FIGS. 7A and 7B according to the number of samples between the maximum value and the minimum value. Select a process.

  Specifically, the addition / subtraction unit 15 performs addition / subtraction processing as follows if the sample interval is from 2 samples to 5 samples. As shown in FIG. 6A, the adder / subtractor 15 adds the difference value Δ (− (−) to the sample data S (−1) and S (+1) immediately before and after the sample data Smax having the maximum value. Correction values obtained by multiplying 1) and Δ (+1) by the coefficients shown in FIG. 5 are added.

  The difference value Δ (−1) is a difference value from the sample data S (−1) immediately before the maximum sample data Smax, and the difference value Δ (+1) is the maximum sample data Smax. This is a difference value from the next sample data S (+1).

  The hatched portion in FIG. 6A is the correction value Vadd added to the sample data S (-1), S (+1).

  Further, as shown in FIG. 6B, the adder / subtractor 15 calculates the difference value Δ from the sample data S (−1) and S (+1) immediately before and after the sample data Smin having the minimum value. A correction value obtained by multiplying (−1) and Δ (+1) by the coefficient shown in FIG. 5 is subtracted.

  The hatched portion in FIG. 6B is the correction value Vsub subtracted from the sample data S (-1) and S (+1).

  The addition / subtraction unit 15 performs addition / subtraction processing as follows if the sample interval is 6 samples or more. As shown in FIG. 7A, the adder / subtractor 15 samples the sample data S (−1), S (−2) one before, two before, one after, and two after the maximum sample data Smax. ), S (+1), S (+2) are corrected by multiplying the difference values Δ (-1), Δ (-2), Δ (+1), Δ (+2) by the coefficients shown in FIG. Add the values.

  The difference value Δ (−2) is the difference value between the previous sample data S (−1) and the previous sample data S (−2), and the difference value Δ (+2) is one. This is a difference value between the subsequent sample data S (+1) and the second sample data S (+2).

  Similarly, the hatched portion in FIG. 7A is the correction value Vadd added to the sample data S (-1), S (-2), S (+1), S (+2). .

  Further, as shown in FIGS. 7A and 7B, the adder / subtractor 15 samples the sample data S (−1 before, after, and after the sample data Smin of the minimum value. ), S (−2), S (+1), and S (+2), the difference values Δ (−1), Δ (−2), Δ (+1), and Δ (+2) are shown in FIG. The correction value multiplied by the indicated coefficient is subtracted.

  Similarly, the hatched portion in FIG. 7B is the correction value Vsub subtracted from the sample data S (-1), S (-2), S (+1), S (+2). .

  The addition / subtraction unit 15 adds the correction value to the sample data near the maximum value and subtracts the correction value from the sample data near the minimum value based on the basic idea as described above.

  Based on the basic idea shown in FIGS. 6A and 6B, if the interval between the maximum value and the minimum value is two sample intervals, the intermediate sample data between the maximum value and the minimum value is obtained. In this case, both addition processing and subtraction processing are performed. In order to avoid this, it is preferable that the addition / subtraction unit 15 performs only addition processing on the intermediate sample data in the case of two sample intervals.

  When the sample value increases from the minimum value to the maximum value as shown in FIG. 4, the addition / subtraction unit 15 performs only addition processing on the intermediate sample data, and the sample value decreases from the maximum value to the minimum value. In this case, only the subtraction process may be performed on the intermediate sample data.

  In the present embodiment, the addition / subtraction unit 15 performs only addition processing on intermediate sample data in the case of two sample intervals.

  By the way, the case where the sample interval is divided into 2 samples to 5 samples and 6 samples or more is merely an example, and is not limited thereto. In addition, the correction value is added to the sample data before, after, or after the maximum sample data Smax, and the sample after the third, third, or subsequent samples of the minimum sample data Smin. The correction value may be subtracted from the data.

  As shown in FIG. 4, the HR audio signal input to the adder / subtractor 15 includes sample data S5 to S7 between the maximum sample data S8 and the previous sample data S4. 15 executes the following addition process.

  The correction value calculation unit 14 multiplies each of the difference values of the sample data S4 and S5, the difference values of the sample data S5 and S6, the difference values of the sample data S6 and S7, and the difference values of the sample data S7 and S8 by a coefficient. Calculate the value. As shown in FIG. 8, the addition / subtraction unit 15 adds the correction value Vadd1 to each of the sample data S4 to S7.

  The adder / subtractor 15 may calculate a correction value Vadd1 obtained by multiplying the sample data S8 having the maximum value by the coefficient of the difference value between the sample data S7 and S8.

  As shown in FIG. 8, adding the correction value Vadd1 to each of the sample data S4 to S7 means that the difference value Δ (-1) is added to the previous sample data S (-1) shown in FIG. This is equivalent to adding a correction value Vadd obtained by multiplying by a coefficient.

  Next, the operation of the waveform correction processing unit 2 shown in FIG. 3 will be described with reference to FIGS.

  The extreme value calculation unit 21 calculates a local maximum value and a local minimum value by determining the size relationship between adjacent sample data in the sample data of the HR audio signal corrected by the waveform correction processing unit 1. That is, the extreme value calculation unit 21 calculates a local maximum value and a local minimum value based on all the sample data of the input HR audio signal.

  The maximum value and the minimum value calculated by the extreme value calculation unit 21 are not necessarily the same as the maximum value and the minimum value calculated by the extreme value calculation unit 11 of FIG. Therefore, it is preferable to calculate the maximum value and the minimum value in each of the waveform correction processing unit 1 and the waveform correction processing unit 2.

  Here, it is assumed that the maximum value and the minimum value calculated by the extreme value calculation unit 21 are the same as the maximum value and the minimum value calculated by the extreme value calculation unit 11. The extreme value calculation unit 21 calculates that the sample data S0 in FIG. 8 is a minimum value and the sample data S8 is a maximum value.

  The sample number detection unit 22 detects the number of samples (sample interval) between the maximum value and the minimum value. The number of samples here is the number of samples at the sample interval T1 of the HR audio signal. In the case of FIG. 8, the sample number detection unit 22 detects that the interval is 8 samples.

  The difference value calculation unit 23 receives the detection result from the sample number detection unit 22 and the HR audio signal. The difference value calculation unit 23 calculates a difference value between adjacent sample data in the HR audio signal. The adjacent sample data here is adjacent sample data at the sample interval T1 of the HR audio signal.

  The correction value calculation unit 24 calculates a correction value by multiplying a difference value between adjacent sample data by a predetermined coefficient. The coefficient is a number less than one. A coefficient corresponding to the number of samples is set in the correction value calculation unit 24. The correction value calculation unit 24 selects a coefficient according to the number of samples detected by the sample number detection unit 22.

  Preferably, a level selection signal is input to the correction value calculation unit 24, and the correction value can be adjusted by selecting a coefficient by which the difference value is multiplied by the level selection signal.

  The level selection signal input to the correction value calculation unit 24 may be the same as the level selection signal input to the correction value calculation unit 14. That is, the level selection signal may be input to the correction value calculation unit 14 and the correction value calculation unit 24 in common.

  The addition / subtraction unit 25 adds the correction value to the sample data near the maximum value, and subtracts the correction value from the sample data near the minimum value. In addition, the addition / subtraction unit 25 may add a correction value to the sample data of the maximum value and subtract the correction value from the sample data of the minimum value.

  The addition / subtraction unit 25 also adds the correction value to the sample data in the vicinity of the maximum value and subtracts the correction value from the sample data in the vicinity of the minimum value based on the idea described with reference to FIGS.

  The sample number detection unit 22 detects that the interval between the minimum value and the maximum value is 8 sample intervals. Therefore, as described with reference to FIG. 7A, the addition / subtraction unit 25 adds the correction value Vadd to the sample data S7 immediately before the sample data S8 having the maximum value and the sample data S6 two times before.

  Specifically, the correction value calculation unit 24 calculates the correction value by multiplying the difference value between the sample data S6 and S7 and the difference value between the sample data S7 and S8 by a coefficient. As shown in FIG. 9, the addition / subtraction unit 25 adds the correction value Vadd2 to each of the sample data S6 and S7, and subtracts the correction value Vsub2 from each of the sample data S1 and S2.

  By the waveform correction process described above, as shown in FIG. 9, the correction value Vadd1 is added to the sample data S4 to S7, the correction value Vadd2 is further added to the sample data S6 and S7, and the sample data S1, S2 Thus, the correction value Vsub2 is subtracted.

  According to the digital audio processing method of this embodiment executed by the digital audio processing device of this embodiment and the digital audio processing device shown in FIG. 1 to FIG. The sound quality of the digital audio signal can be improved.

  FIG. 10 shows a correction waveform in a case where the interval between the sample data S0 having the minimum value and the sample data S12 having the maximum value is a sample interval T0 of the CD audio signal and is 3 sample intervals.

  The waveform correction processing unit 1 adds the correction value Vadd1 to the sample data S8 to S11, and subtracts the correction value Vsub1 from the sample data S1 to S4. The waveform correction processing unit 2 adds the correction value Vadd2 to the sample data S10 and S11, and subtracts the correction value Vsub2 from the sample data S1 and S2.

  The operation of the digital sound processing apparatus of the present embodiment described above and the processing of the digital sound processing method of the present embodiment can be executed by a digital sound processing program.

  As shown in FIG. 11, the microcomputer 30 is connected with a recording medium 40 in which a digital audio processing program is stored. The recording medium 40 is an arbitrary non-temporary recording medium (storage medium) such as a hard disk drive, an optical disk, or a semiconductor memory. The digital audio processing program may be transmitted from an external server via a communication line such as the Internet and recorded on the recording medium 40.

  The digital audio processing program may cause the microcomputer 30 to execute the process of each step as shown in FIG.

  Extraction step S101: The digital audio processing program causes the microcomputer 30 to execute a process of extracting sample data at the sample interval of the first digital audio signal from the sample data constituting the digital audio signal to be processed.

  First extreme value calculation step S102: The digital audio processing program causes the microcomputer 30 to execute a process of calculating the maximum value sample data and the minimum value sample data based on the sample data extracted in the extraction step. .

  First sample number detection step S103: The digital audio processing program causes the microcomputer 30 to execute a process of detecting the number of samples between adjacent maximum value sample data and minimum value sample data.

  First difference value calculation step S104: The digital audio processing program causes the microcomputer 30 to execute a process of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed.

  First correction value calculation step S105: The digital sound processing program executes a process of calculating a correction value by multiplying the microcomputer 30 by a predetermined coefficient to the difference value calculated in the first difference value calculation step S104. Let

  First addition / subtraction step S106: The digital audio processing program causes the microcomputer 30 to sample at least the maximum value calculated in the first extreme value calculation step S102 among the sample data constituting the digital audio signal to be processed. Included between the previous and next sample data adjacent to the data and the previous and next sample data adjacent to the maximum sample data at the sample interval of the first digital audio signal A process of adding the correction value calculated in the first correction value calculation step S105 to each sample data is executed.

  In addition, the digital audio processing program stores at least one sample data before and after the sample data adjacent to the sample data of the minimum value calculated in the first extreme value calculation step S102 in the microcomputer 30; The correction calculated in the first correction value calculation step S105 from the respective sample data included between the previous sample data and the next sample data adjacent to the minimum sample data at the sample interval of the digital audio signal. Causes the value to be subtracted.

  Second extreme value calculation step S202: The digital audio processing program causes the microcomputer 30 to sample the maximum value based on the sample data constituting the processing target digital audio signal subjected to the addition / subtraction process in the first addition / subtraction step S106. A process of calculating the data and the sample data of the minimum value is executed.

  Second sample number detection step S203: The digital audio processing program causes the microcomputer 30 to execute a process of detecting the number of samples between adjacent maximum value sample data and minimum value sample data.

  Second difference value calculation step S204: The digital audio processing program causes the microcomputer 30 to execute a process of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed.

  Second correction value calculation step S205: The digital audio processing program executes a process of calculating a correction value by causing the microcomputer 30 to multiply the difference value calculated in the second difference value calculation step S204 by a predetermined coefficient. Let

  Second addition / subtraction step S206: The digital audio processing program causes the microcomputer 30 to sample at least the maximum value calculated in the second extreme value calculation step S202 among the sample data constituting the digital audio signal to be processed. A process of adding the correction value calculated in the second correction value calculation step S205 to the sample data immediately before and after the data adjacent to the data is executed.

  In addition, the digital audio processing program causes the microcomputer 30 to input the second sample data before and after the sample data of the minimum value calculated in the second extreme value calculation step S202. A process of subtracting the correction value calculated in the correction value calculation step S205 is executed.

  In the digital audio processing apparatus, digital audio processing method, and digital audio processing program of the present embodiment described above, the waveform correction processing in the waveform correction processing unit 1 and the waveform correction processing in the waveform correction processing unit 2 are shown in FIG. The table shown is commonly used. Separate tables may be used for the waveform correction processing in the waveform correction processing unit 1 and the waveform correction processing in the waveform correction processing unit 2.

  The maximum sample interval may be different between the table used in the waveform correction processing in the waveform correction processing unit 1 and the table used in the waveform correction processing in the waveform correction processing unit 2.

  For example, in the waveform correction processing in the waveform correction processing unit 1, a table in which correction values are set at intervals of 2 to 8 samples is used, and in the waveform correction processing in the waveform correction processing unit 2, correction values are set at intervals of 2 to 32 samples. Can be used.

  The coefficients may be different between the table used in the waveform correction processing in the waveform correction processing unit 1 and the table used in the waveform correction processing in the waveform correction processing unit 2.

  The sample data range in which the correction value is added / subtracted in the waveform correction processing in the waveform correction processing unit 1 may be different from the sample data range in which the correction value is added / subtracted in the waveform correction processing unit 2.

  For example, in the waveform correction processing in the waveform correction processing unit 1, the correction value is added or subtracted from the maximum value or the minimum value up to the next two samples in the sample data of the first digital audio signal, and the waveform correction processing in the waveform correction processing unit 2 Then, the correction value may be added to or subtracted from the maximum value or the minimum value up to a maximum of 8 samples next to the sample data of the second digital audio signal.

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

1, 2 Waveform correction processing unit 11, 21 Extreme value calculation unit 12, 22 Sample number detection unit 13, 23 Difference value calculation unit 14, 24 Correction value calculation unit 15, 25 Addition / subtraction unit 30 Microcomputer 40 Recording medium

Claims (5)

A digital audio signal obtained by converting a first digital audio signal having a first sampling frequency into a second digital audio signal having a second sampling frequency higher than the first sampling frequency is used as a digital audio signal to be processed. ,
A first waveform correction processing unit for correcting the waveform of the digital audio signal to be processed;
A second waveform correction processing unit that corrects a waveform of the digital audio signal to be processed whose waveform is corrected by the first waveform correction processing unit;
With
The first waveform correction processing unit
Of the sample data constituting the digital audio signal to be processed, sample data is extracted at the sample interval of the first digital audio signal, and based on the extracted sample data, the maximum value sample data and the minimum value sample are extracted. A first extreme value calculation unit for calculating data;
A first sample number detector for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A first difference value calculation unit for calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A first correction value calculation unit that calculates a correction value by multiplying the difference value calculated by the first difference value calculation unit by a predetermined coefficient;
Of the sample data constituting the digital audio signal to be processed, at least one sample data before and after the sample data adjacent to the sample data of the maximum value calculated by the first extreme value calculation unit, The first correction value calculation unit applies each sample data included between the previous sample data and the next sample data adjacent to the maximum sample data at the sample interval of the first digital audio signal. The calculated correction value is added, and at least one sample data before and after the sample data of the minimum value calculated by the first extreme value calculation unit, and the first digital audio signal From the respective sample data included between the previous sample data and the next sample data adjacent to the minimum sample data at the sample interval of A first subtraction unit for subtracting the correction value calculated by the first correction value calculation unit,
Have
The second waveform correction processing unit includes:
A second extreme value calculation unit that calculates maximum value sample data and minimum value sample data based on sample data constituting the digital audio signal to be processed output from the first waveform correction processing unit When,
A second sample number detection unit for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A second difference value calculation unit for calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A second correction value calculation unit that calculates a correction value by multiplying the difference value calculated by the second difference value calculation unit by a predetermined coefficient;
Among the sample data constituting the digital audio signal to be processed, at least one sample data before and after one adjacent to the sample data of the maximum value calculated by the second extreme value calculation unit, The correction value calculated by the second correction value calculation unit is added, and at least from the sample data immediately before and after the sample data of the minimum value calculated by the second extreme value calculation unit A second addition / subtraction unit for subtracting the correction value calculated by the second correction value calculation unit;
A digital audio processing apparatus characterized by comprising: The first addition / subtraction unit includes:
When the number of samples detected by the first sample number detection unit is included in the first range, the one before and one adjacent to the sample data of the maximum value calculated by the first extreme value calculation unit Each sample data included between the next sample data and the previous and next sample data adjacent to the maximum sample data at the sample interval of the first digital audio signal; The correction value calculated by the first correction value calculation unit is added, and the sample data immediately before and after the one adjacent to the sample data of the minimum value calculated by the first extreme value calculation unit, From the respective sample data included between the previous sample data and the next sample data adjacent to the minimum sample data at the sample interval of the first digital audio signal, the first Subtracting the correction value calculated by the positive value calculation unit,
When the number of samples detected by the first sample number detection unit is included in the second range that is larger than the number of samples included in the first range, the first extreme value calculation unit calculates One sample data before and after the sample data adjacent to the maximum sample data, and one sample data before and after the sample data adjacent to the sample data of the maximum value at the sample interval of the first digital audio signal , Sample data before and after the sample interval of the first digital audio signal, and two samples at the sample interval of the first digital audio signal. The correction value calculated by the first correction value calculation unit is added to each sample data included between the previous and second sample data, and the first pole One sample data before and after the sample data of the minimum value calculated by the calculation unit, one sample data of the first digital audio signal and one sample before the sample of the minimum value Respective sample data included between the first sample data and the sample data before and after the first digital audio signal in the sample interval of the first digital audio signal, and the first digital audio signal The correction value calculated by the first correction value calculation unit is subtracted from the respective sample data included between the sample data before and after the two samples in the sample interval,
The second addition / subtraction unit
When the number of samples detected by the second sample number detection unit is included in the first range, the previous one adjacent to the maximum value sample data calculated by the second extreme value calculation unit and The correction value calculated by the second correction value calculation unit is added to the next sample data, and the previous one adjacent to the sample data of the minimum value calculated by the second extreme value calculation unit and Subtract the correction value calculated by the second correction value calculation unit from the next sample data,
When the number of samples detected by the second sample number detection unit is included in the second range, the previous one adjacent to the sample data of the maximum value calculated by the second extreme value calculation unit and The correction value calculated by the second correction value calculation unit is added to the sample data after one and the sample data before and after the second, and the minimum calculated by the second extreme value calculation unit. The correction value calculated by the second correction value calculation unit is subtracted from the sample data immediately before and after the sample data adjacent to the value sample data and the sample data after the previous and second samples. The digital audio processing apparatus according to claim 1. When N is a natural number of 2 or more, the second sampling frequency is N times the first sampling frequency,
The digital audio processing apparatus according to claim 1 or 2, wherein the first extreme value calculation unit extracts sample data for every N samples of sample data constituting the digital audio signal to be processed. A digital audio signal obtained by converting a first digital audio signal having a first sampling frequency into a second digital audio signal having a second sampling frequency higher than the first sampling frequency is used as a digital audio signal to be processed. ,
An extraction step of extracting sample data at a sample interval of the first digital audio signal among sample data constituting the digital audio signal to be processed;
Based on the sample data extracted in the extraction step, a first extreme value calculating step of calculating sample data of a maximum value and sample data of a minimum value;
A first sample number detection step for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A first difference value calculating step of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A first correction value calculating step of calculating a correction value by multiplying the difference value calculated in the first difference value calculating step by a predetermined coefficient;
Among the sample data constituting the digital audio signal to be processed, at least one sample data before and after the sample data adjacent to the sample data of the maximum value calculated in the first extreme value calculation step, In the first correction value calculation step, each sample data included between the sample data immediately before and after the maximum sample data at the sample interval of the first digital audio signal is included in the first correction value calculation step. The calculated correction value is added, at least one sample data before and after the sample data of the minimum value calculated in the first extreme value calculation step, and the first digital audio signal From the respective sample data included between the previous sample data and the next sample data adjacent to the minimum sample data at the sample interval of A first subtraction step of subtracting the correction value calculated by the first correction value calculation step,
A second extreme value calculating step for calculating a maximum value sample data and a minimum value sample data based on the sample data constituting the processing target digital audio signal subjected to the addition / subtraction process in the first addition / subtraction step; ,
A second sample number detection step for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A second difference value calculating step of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A second correction value calculating step of calculating a correction value by multiplying the difference value calculated in the second difference value calculating step by a predetermined coefficient;
Among the sample data constituting the digital audio signal to be processed, at least one sample data before and after one adjacent to the sample data of the maximum value calculated in the second extreme value calculation step, The correction values calculated in the second correction value calculation step are added, and at least from the sample data immediately before and after the sample data of the minimum value calculated in the second extreme value calculation step. A second addition / subtraction step for subtracting the correction value calculated in the second correction value calculation step;
A digital audio processing method characterized by comprising: A digital audio signal obtained by converting a first digital audio signal having a first sampling frequency into a second digital audio signal having a second sampling frequency higher than the first sampling frequency is used as a digital audio signal to be processed. ,
On the computer,
An extraction step of extracting sample data at a sample interval of the first digital audio signal among sample data constituting the digital audio signal to be processed;
Based on the sample data extracted in the extraction step, a first extreme value calculating step of calculating sample data of a maximum value and sample data of a minimum value;
A first sample number detection step for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A first difference value calculating step of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A first correction value calculating step of calculating a correction value by multiplying the difference value calculated in the first difference value calculating step by a predetermined coefficient;
Among the sample data constituting the digital audio signal to be processed, at least one sample data before and after the sample data adjacent to the sample data of the maximum value calculated in the first extreme value calculation step, In the first correction value calculation step, each sample data included between the sample data immediately before and after the maximum sample data at the sample interval of the first digital audio signal is included in the first correction value calculation step. The calculated correction value is added, at least one sample data before and after the sample data of the minimum value calculated in the first extreme value calculation step, and the first digital audio signal From the respective sample data included between the previous sample data and the next sample data adjacent to the minimum sample data at the sample interval of A first subtraction step of subtracting the correction value calculated by the first correction value calculation step,
A second extreme value calculating step for calculating a maximum value sample data and a minimum value sample data based on the sample data constituting the processing target digital audio signal subjected to the addition / subtraction process in the first addition / subtraction step; ,
A second sample number detection step for detecting the number of samples between adjacent maximum value sample data and minimum value sample data;
A second difference value calculating step of calculating a difference value between adjacent sample data in the sample data constituting the digital audio signal to be processed;
A second correction value calculating step of calculating a correction value by multiplying the difference value calculated in the second difference value calculating step by a predetermined coefficient;
Among the sample data constituting the digital audio signal to be processed, at least one sample data before and after one adjacent to the sample data of the maximum value calculated in the second extreme value calculation step, The correction values calculated in the second correction value calculation step are added, and at least from the sample data immediately before and after the sample data of the minimum value calculated in the second extreme value calculation step. A second addition / subtraction step for subtracting the correction value calculated in the second correction value calculation step;
A digital audio processing program characterized in that

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