Digital audio processing device, digital audio processing method, digital audio processing program

Abstract

The present invention provides a digital audio processing device that can generate harmonic signals ideal for improving sound quality, even when the digital audio signal contains waveforms with multiple consecutive samples of the same value as a maximum or minimum sample. [Solution] The maximum / minimum sample detection unit 11 detects the maximum and minimum samples in a series of samples that constitute a digital audio signal. The maximum / minimum sample correction unit 12, when there are consecutive samples with the same value as the maximum or minimum sample, assigns a maximum sample tag or a minimum sample tag to samples that are different from the maximum or minimum sample among the consecutive samples. If no consecutive samples exist, the maximum / minimum sample correction unit 12 assigns a maximum sample tag to the maximum sample and a minimum sample tag to the minimum sample.

Description

Technical Field

[0001] The present invention relates to a digital audio processing device, a digital audio processing method, and a digital audio processing program.

Background Art

[0002] Patent Document 1 describes a digital audio processing device and a digital audio processing method capable of improving the sound quality in terms of auditory perception when a digital audio signal is reproduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the digital audio processing device and the digital audio processing method described in Patent Document 1, a correction value is added to a sample adjacent to a maximum sample having a maximum value in the waveform of a digital audio signal, and the correction value is subtracted from a sample adjacent to a minimum sample having a minimum value. At this time, the digital audio processing device and the digital audio processing method determine the correction value according to the number of samples between adjacent maximum samples and minimum samples. In the digital audio processing device and the digital audio processing method described in Patent Document 1, a waveform in which a plurality of samples having the same value as the maximum sample or the minimum sample are continuous is not assumed.

[0005] When an analog audio signal is sampled and converted into a digital audio signal, or when the digital audio signal is compressed, a waveform in which a plurality of samples having the same value as the maximum sample or the minimum sample may be continuous.

[0006] In a waveform where multiple consecutive samples have the same value as a maximum or minimum sample, it is possible that the sample that is actually the true maximum or minimum is not the sample that was determined to be the maximum or minimum sample, but rather one of the other consecutive samples with the same value. The digital audio processing device and digital audio processing method described in Patent Document 1 may fail to generate an ideal harmonic signal for improving sound quality if the digital audio signal contains a waveform where multiple consecutive samples have the same value as a maximum or minimum sample, by incorrectly detecting the number of samples between adjacent maximum and minimum samples.

[0007] The present invention aims to provide a digital audio processing device, a digital audio processing method, and a digital audio processing program that can generate harmonic signals ideal for improving sound quality, even when the digital audio signal contains a waveform in which multiple consecutive samples have the same value as a maximum or minimum sample. [Means for solving the problem]

[0008] The present invention includes a maximum / minimum sample detection unit that detects a maximum sample and a minimum sample in a series of samples constituting an input digital audio signal, and when there is a first consecutive sample in which two or more samples with the same value as the maximum sample detected by the maximum / minimum sample detection unit are consecutive, including the maximum sample, a maximum sample tag is assigned to a sample from the first consecutive sample that is different from the maximum sample, when there are no two or more samples with the same value as the maximum sample detected by the maximum / minimum sample detection unit including the maximum sample, a maximum sample tag is assigned to the maximum sample, when there is a second consecutive sample in which two or more samples with the same value as the minimum sample detected by the maximum / minimum sample detection unit are consecutive, including the minimum sample, a minimum sample tag is assigned to a sample from the second consecutive sample that is different from the minimum sample, and the minimum sample detected by the maximum / minimum sample detection unit and A digital audio processing device is provided, comprising: a maximum / minimal sample correction unit that assigns a minimal sample tag to a minimal sample when there are no two or more consecutive samples with the same value, including the minimal sample; a sample count detection unit that detects the number of adjacent samples between a sample to which the maximum sample tag has been assigned and a sample to which the minimal sample tag has been assigned; a difference value calculation unit that calculates the difference value between adjacent samples in the series of samples; a correction value calculation unit that calculates a correction value by multiplying the difference value calculated by the difference value calculation unit by a predetermined coefficient corresponding to the number of samples detected by the sample count detection unit; and an addition / subtraction unit that adds the correction value calculated by the correction value calculation unit to at least the sample immediately preceding and immediately following the sample to which the maximum sample tag has been assigned, and subtracts the correction value calculated by the correction value calculation unit from at least the sample immediately preceding and immediately following the sample to which the minimal sample tag has been assigned.

[0009] The present invention detects a maximum sample and a minimum sample in a series of samples constituting an input digital audio signal, and when there is a first sequence of two or more consecutive samples including the maximum sample in which samples with the same value as the detected maximum sample exist, a maximum sample tag is assigned to a sample different from the maximum sample from the first sequence of samples; when there are no two or more consecutive samples including the maximum sample in which samples with the same value as the detected maximum sample exist, a maximum sample tag is assigned to the maximum sample; when there is a second sequence of two or more consecutive samples including the minimum sample in which samples with the same value as the detected minimum sample exist, a minimum sample tag is assigned to a sample different from the minimum sample from the second sequence of samples; when there are no two or more consecutive samples including the minimum sample in which samples with the same value as the detected minimum sample exist, a minimum sample tag is assigned to the minimum sample; and the number of adjacent samples between a sample with the maximum sample tag and a sample with the minimum sample tag is detected. The present invention provides a digital audio processing method which involves calculating the difference between adjacent samples in the series of samples, calculating a correction value by multiplying the calculated difference value by a predetermined coefficient corresponding to the number of detected samples, adding the correction value to at least the sample immediately preceding and immediately following the sample to which the maximum sample tag is attached, and subtracting the correction value from at least the sample immediately preceding and immediately following the sample to which the minimum sample tag is attached.

[0010] The present invention provides a computer with the steps of: detecting a maximum sample and a minimum sample in a series of samples constituting an input digital audio signal; when there is a first sequence of two or more consecutive samples including the maximum sample in which samples with the same value as the detected maximum sample exist, assigning a maximum sample tag to a sample different from the maximum sample from the first sequence of samples; when there are no two or more consecutive samples including the maximum sample in which samples with the same value as the detected maximum sample exist, assigning a maximum sample tag to the maximum sample; when there is a second sequence of two or more consecutive samples including the minimum sample in which samples with the same value as the detected minimum sample exist, assigning a minimum sample tag to a sample different from the minimum sample from the second sequence of samples; and detection The present invention provides a digital audio processing program that performs the following steps when there are no two or more consecutive samples with the same value as the given minimum sample, including the minimum sample: assigning a minimum sample tag to the minimum sample; detecting the number of adjacent samples between the sample assigned the maximum sample tag and the sample assigned the minimum sample tag; calculating the difference value of adjacent samples in the series of samples; calculating a correction value by multiplying the calculated difference value by a predetermined coefficient corresponding to the number of detected samples; and adding the correction value to at least the sample immediately preceding and immediately following the sample assigned the maximum sample tag, and subtracting the correction value from at least the sample immediately preceding and immediately following the sample assigned the minimum sample tag. [Effects of the Invention]

[0011] According to the digital audio processing device, digital audio processing method, and digital audio processing program of the present invention, even if the digital audio signal contains a waveform in which multiple consecutive samples have the same value as the maximum or minimum sample, it is possible to generate a harmonic signal that is ideal for improving sound quality. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a block diagram showing a digital audio processing device according to one embodiment. [Figure 2A] Figure 2A is a waveform diagram showing an example of the waveform of an audio signal input to a digital audio processing device according to one embodiment. [Figure 2B] Figure 2B is a waveform diagram showing the state after an addition / subtraction operation has been performed on the waveform shown in Figure 2A by a digital audio processing device according to one embodiment. [Figure 3] Figure 3 shows an example of a table of correction values ​​set for each sample size between the maximum and minimum samples. [Figure 4A] Figure 4A shows a corrected waveform obtained by adding correction values ​​to the sample immediately before and immediately after the maximum sample in a digital audio processing device according to one embodiment. [Figure 4B] Figure 4B shows a corrected waveform obtained by subtracting a correction value from the sample immediately preceding and immediately following the minimum sample in a digital audio processing device according to one embodiment. [Figure 5A] Figure 5A shows a corrected waveform obtained by adding correction values ​​to the sample one, two samples before, one, and two samples after the maximum sample, as performed by the addition / subtraction unit of a digital audio processing device according to one embodiment. [Figure 5B] Figure 5B shows a corrected waveform obtained by subtracting a correction value from the sample one, two samples before, one, and two samples after the minimum sample, using an addition / subtraction unit in a digital audio processing device according to one embodiment. [Figure 6] Figure 6 shows an example of a waveform in which multiple consecutive samples have the same value as the maximum sample. [Figure 7] Figure 7 is a conceptual diagram illustrating the correction operation of the maximum sample size by the maximum / minimum sample correction unit of a digital audio processing device according to one embodiment. [Figure 8] Figure 8 shows a corrected waveform obtained by applying addition and subtraction processing to a waveform in which the maximum sample correction unit has corrected the maximum sample, using an addition / subtraction unit provided in a digital audio processing device according to one embodiment. [Figure 9] FIG. 9 is a diagram showing an example of a waveform in which a plurality of samples having the same value as the minimum sample are continuous. [Figure 10] FIG. 10 is a diagram conceptually showing a correction operation of a minimum sample by a maximum / minimum sample correction unit included in a digital audio processing apparatus according to an embodiment. [Figure 11] FIG. 11 is a diagram showing a corrected waveform obtained by subjecting the waveform in which the minimum sample is corrected by the maximum / minimum sample correction unit to an addition / subtraction process by an addition / subtraction unit included in a digital audio processing apparatus according to an embodiment. [Figure 12] FIG. 12 is a diagram for explaining a calculation formula used when the maximum / minimum sample correction unit included in a digital audio processing apparatus according to an embodiment corrects a maximum sample. [Figure 13] FIG. 13 is a diagram for explaining a calculation formula used when the maximum / minimum sample correction unit included in a digital audio processing apparatus according to an embodiment corrects a minimum sample. [Figure 14] FIG. 14 is a flowchart showing operations of a digital audio processing apparatus according to an embodiment, a digital audio processing method according to an embodiment, and processes to be executed by a computer by a digital audio processing program according to an embodiment. [Figure 15] FIG. 15 is a flowchart showing specific processing of step S33 shown in FIG. 14. [Figure 16] FIG. 16 is a block diagram showing a configuration example of a microcomputer that executes a digital audio processing program according to an embodiment.

Embodiments for Carrying Out the Invention

[0013] 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.

[0014] As shown in Figure 1, the digital audio processing device 100 according to one embodiment includes a maximum / minimum sample detection unit 11, a maximum / minimum sample correction unit 12, a sample count detection unit 13, a difference value calculation unit 14, a correction value calculation unit 15, and an addition / subtraction unit 16. The maximum / minimum sample correction unit 12 is a configuration unique to the digital audio processing device according to one embodiment, and is not included in the digital audio processing device described in Patent Document 1.

[0015] First, the basic operation of the digital audio processing device 100 will be explained. As an example, the digital audio signal (hereinafter referred to as the audio signal) input to the digital audio processing device 100 will not contain a waveform in which two or more consecutive samples have the same value as the maximum or minimum sample, but rather a waveform in which the maximum and minimum samples exist individually.

[0016] In Figure 1, the maximum / minimum sample detection unit 11 receives, as an example, an audio signal with 24 bits of quantization and a sampling frequency of 96 kHz. The maximum / minimum sample detection unit 11 detects maximum samples (samples with a maximum value) and minimum samples (samples with a minimum value) by determining the relative magnitudes of the sample values ​​of adjacent samples in the input audio signal. Specifically, the maximum / minimum sample detection unit 11 detects the sample immediately preceding a sample in which the slope of the audio signal waveform changes from a positive state (including 0) to a negative state as a maximum sample, and the sample immediately preceding a sample in which the slope changes from a negative state (including 0) to a positive state as a minimum sample.

[0017] Figure 2A shows an example of the waveform of an input audio signal. The series of samples that make up the waveform of the audio signal are arranged in the time direction with a sample interval T0. When the waveform of the input audio signal is the waveform shown in Figure 2A, the maximum / minimum sample detection unit 11 detects sample S0 as the minimum sample and sample S3 as the maximum sample. The waveform between the minimum sample S0 and the maximum sample S3 is shown by a thin solid line.

[0018] The waveform shown in Figure 2A does not have two or more consecutive samples with the same value as the maximum or minimum sample. Therefore, the maximum / minimum sample correction unit 12 assigns a maximum sample tag and a minimum sample tag to the maximum and minimum samples detected by the maximum / minimum sample detection unit 11, respectively. In other words, the maximum / minimum sample correction unit 12 does not correct the maximum and minimum samples.

[0019] The sample count detection unit 13 detects the number of samples (sample interval) between adjacent samples that have been tagged with a maximum sample tag and samples that have been tagged with a minimum sample tag. Here, the samples tagged with a maximum sample tag are the maximum samples detected by the maximum / minimum sample detection unit 11, and the samples tagged with a minimum sample tag are the minimum samples detected by the maximum / minimum sample detection unit 11. Hereafter, the number of samples between adjacent maximum and minimum samples may be abbreviated as the sample interval between the maximum and minimum samples, or simply as the sample interval.

[0020] The number of samples between a sample tagged with the maximum sample tag and a sample tagged with the minimum sample tag refers to the number of samples in the portion where the sample value increases from the minimum sample S0 to the maximum sample S3, as shown in Figure 2A, and the number of samples in the portion where the sample value decreases from the maximum sample S3 to a minimum sample (not shown). In the waveform shown in Figure 2A, the sample count detection unit 13 detects that there is a 3-sample interval between the minimum sample S0 and the maximum sample S3. If the sample period is denoted as fs, then the sample interval between the minimum sample S0 and the maximum sample S3 shown in Figure 2A is 3fs.

[0021] The difference value calculation unit 14 calculates the difference value between adjacent samples in the input audio signal. The correction value calculation unit 15 calculates a correction value by multiplying the difference value between adjacent samples by a predetermined coefficient corresponding to the sample interval between the sample with the maximum sample tag and the sample with the minimum sample tag. The coefficient is a number less than or equal to 1.

[0022] Figure 3 shows an example of a coefficient that the correction value calculation unit 15 multiplies by the difference value of adjacent samples. The maximum sample / minimum sample interval shown in Figure 3 refers to the number of samples between a sample tagged with the maximum sample tag and a sample tagged with the minimum sample tag.

[0023] In the digital audio processing device 100 shown in Figure 1, a level selection signal is input to the correction value calculation unit 15, and the device is configured to select a coefficient to be multiplied by the difference value based on the level selection signal. While it is not essential that the correction value be adjustable by selecting the coefficient to be multiplied by the difference value, it is preferable that the correction value be adjustable.

[0024] As shown in Figure 3, the correction value calculation unit 15 has coefficients set in correspondence with level selection signals 00, 01, 10, and 11, ranging from a sample interval of 2 samples to a predetermined number of sample intervals between the maximum and minimum samples. The predetermined number can be set as appropriate. When the level selection signal is 00, the correction value is at its maximum, and as the level selection signal approaches 11, the correction value decreases in order. That is, the harmonic signal added to the audio signal is at its maximum when the level selection signal is 00, and decreases as the level selection signal approaches 11.

[0025] The addition / subtraction unit 16 adds the correction value calculated by the correction value calculation unit 15 to samples near the sample to which the maximum sample tag has been assigned in the input audio signal, and subtracts the correction value calculated by the correction value calculation unit 15 from samples near the sample to which the minimum sample tag has been assigned. Here, the sample to which the maximum sample tag has been assigned and the sample to which the minimum sample tag has been assigned are the samples that have been detected as the maximum sample and the minimum sample by the maximum / minimum sample detection unit 11, respectively. Therefore, the addition / subtraction unit 16 adds the correction value to the samples near the maximum sample and subtracts the correction value from the samples near the minimum sample.

[0026] Using Figures 4A, 4B, 5A, and 5B, we will specifically explain how the addition / subtraction unit 16 adds a correction value to samples near the maximum sample and subtracts a correction value from samples near the minimum sample. In Figures 4A, 4B, 5A, and 5B, Smax represents the maximum sample and Smin represents the minimum sample. Sample S(-1) represents the sample immediately preceding the maximum sample Smax or minimum sample Smin, and sample S(-2) represents the sample two steps before the maximum sample Smax or minimum sample Smin. Sample S(+1) represents the sample immediately following the maximum sample Smax or minimum sample Smin, and sample S(+2) represents the sample two steps after the maximum sample Smax or minimum sample Smin.

[0027] As shown in Figure 4A, the addition / subtraction unit 16 adds the correction value Vadd, calculated by the correction value calculation unit 15 by multiplying the difference value Δ(-1) between the maximum sample Smax and sample S(-1) by a coefficient, to the sample S(-1) adjacent to the maximum sample Smax. The addition / subtraction unit 16 also adds the correction value Vadd, calculated by the correction value calculation unit 15 by multiplying the difference value Δ(+1) between the maximum sample Smax and sample S(+1) by a coefficient, to the sample S(+1) adjacent to the maximum sample Smax. The uncorrected samples S(-1) and S(+1), shown by the dashed lines, are corrected to the samples S(-1)' and S(+1)', shown by the solid lines, by adding the correction value Vadd.

[0028] As shown in Figure 4B, the addition / subtraction unit 16 subtracts the correction value Vsub calculated by the correction value calculation unit 15 by multiplying the difference value Δ(-1) between the minimum sample Smin and sample S(-1) by a coefficient from sample S(-1) adjacent to the minimum sample Smin. The addition / subtraction unit 16 also subtracts the correction value Vsub calculated by the correction value calculation unit 15 by multiplying the difference value Δ(+1) between the minimum sample Smin and sample S(+1) by a coefficient from sample S(+1) adjacent to the minimum sample Smin. The uncorrected samples S(-1) and S(+1), shown by the dashed lines, are corrected to samples S(-1)' and S(+1)', shown by the solid lines, by subtracting the correction value Vsub.

[0029] As an example, the addition / subtraction unit 16 performs the addition / subtraction process shown in Figures 4A and 4B if the sample interval between the maximum sample Smax and the minimum sample Smin is between 2 and 5 samples. If the sample interval is 6 or more, the addition / subtraction unit 16 performs the addition / subtraction process shown in Figures 5A and 5B. Thus, the addition / subtraction unit 16 may select between the addition / subtraction process shown in Figures 4A and 4B and the addition / subtraction process shown in Figures 5A and 5B depending on the sample interval.

[0030] As shown in Figure 5A, the addition / subtraction unit 16 adds the correction value Vadd to sample S(-1) in the same way as in Figure 4A. In addition, the addition / subtraction unit 16 adds the correction value Vadd, calculated by the correction value calculation unit 15 by multiplying the difference value Δ(-2) between sample S(-1) and sample S(-2) by a coefficient, to sample S(-2), which is two samples before the maximum sample Smax. The addition / subtraction unit 16 adds the correction value Vadd to sample S(+1) in the same way as in Figure 4A. In addition, the addition / subtraction unit 16 adds the correction value Vadd, calculated by the correction value calculation unit 15 by multiplying the difference value Δ(+2) between sample S(+1) and sample S(+2) by a coefficient, to sample S(+2), which is two samples after the maximum sample Smax.

[0031] The uncorrected samples S(-1), S(-2), S(+1), and S(+2), shown by the dashed lines, are corrected to the samples S(-1)', S(-2)', S(+1)', and S(+2)', shown by the solid lines, by adding the correction value Vadd.

[0032] As shown in Figure 5B, the addition / subtraction unit 16 subtracts the correction value Vsub from sample S(-1) in the same way as in Figure 4B. In addition, the addition / subtraction unit 16 subtracts the correction value Vsub calculated by the correction value calculation unit 15 by multiplying the difference value Δ(-2) between sample S(-1) and sample S(-2) by a coefficient from sample S(-2), which is two samples prior to the minimum sample Smin. The addition / subtraction unit 16 subtracts the correction value Vsub from sample S(+1) in the same way as in Figure 4B. In addition, the addition / subtraction unit 16 subtracts the correction value Vsub calculated by the correction value calculation unit 15 by multiplying the difference value Δ(+2) between sample S(+1) and sample S(+2) by a coefficient from sample S(+2), which is two samples after the minimum sample Smin.

[0033] The uncorrected samples S(-1), S(-2), S(+1), and S(+2), shown by the dashed lines, are corrected to the samples S(-1)', S(-2)', S(+1)', and S(+2)', shown by the solid lines, by subtracting the correction value Vsub.

[0034] The addition / subtraction unit 16 adds the correction value Vadd to samples near the maximum sample and subtracts the correction value Vsub from samples near the minimum sample, thereby outputting an audio signal with harmonic signals added from the addition / subtraction unit 16. The difference value calculation unit 14 may calculate only the difference between the sample to which the addition / subtraction unit 16 adds or subtracts the correction value Vadd or correction value Vsub, and its adjacent samples.

[0035] When the sample interval between the maximum sample Smax and the minimum sample Smin is 2 samples, following the addition and subtraction process shown in Figures 4A and 4B would result in both addition and subtraction being applied to the intermediate samples between the maximum sample Smax and the minimum sample Smin. To avoid this, it is preferable for the addition / subtraction unit 16 to apply only addition to the intermediate samples when the sample interval is 2 samples. The addition / subtraction unit 16 may also apply only addition to the intermediate samples when the sample value increases from the minimum sample Smin to the maximum sample Smax, and apply only subtraction to the intermediate samples when the sample value decreases from the maximum sample Smax to the minimum sample Smin.

[0036] Since the waveform shown in Figure 2A is at a 3-sample interval, the addition / subtraction unit 16 performs the addition / subtraction processing shown in Figures 4A and 4B. As shown in Figure 2B, the uncorrected sample S1, shown by the dashed line, is corrected to the sample S1' shown by the solid line by subtracting the correction value Vsub, and the sample value decreases as indicated by the arrow. The uncorrected sample S2, shown by the dashed line, is corrected to the sample S2' shown by the solid line by adding the correction value Vadd, and the sample value increases as indicated by the arrow. The waveform shown by the dashed line between the minimum sample S0 and the maximum sample S3 is corrected to the waveform shown by the thin solid line. The waveform shown by the dashed line in Figure 2B corresponds to the waveform shown by the thin solid line in Figure 2A.

[0037] The distinction between the sample intervals of 2 to 5 samples and 6 or more samples between the maximum and minimum samples is merely an example. The addition / subtraction unit 16 may perform only the addition / subtraction processes shown in Figures 4A and 4B when the sample interval between the maximum and minimum samples is from 2 samples to a predetermined number of sample intervals. When the addition / subtraction unit 16 selects between the addition / subtraction processes shown in Figures 4A and 4B and the addition / subtraction processes shown in Figures 5A and 5B, it may perform the addition / subtraction processes shown in Figures 5A and 5B for sample intervals greater than 6 samples. The addition / subtraction unit 16 may add correction values ​​to the samples three before and three after the maximum sample, or thereafter, and subtract correction values ​​from the samples three before and three after the minimum sample, or thereafter.

[0038] The addition / subtraction unit 16 only needs to add a correction value Vadd to at least the sample immediately preceding and succeeding the maximum sample in the series of samples, and subtract a correction value Vsub from at least the sample immediately preceding and succeeding the minimum sample.

[0039] Next, the operation of the digital audio processing device 100 when the audio signal input to the digital audio processing device 100 includes the waveform shown in Figure 6 will be explained. As shown in Figure 6, the sample values ​​increase sequentially from the minimum sample S0 to sample S3, and samples with the same value are consecutive from sample S3 to sample S6. The sample values ​​decrease sequentially from sample S6 to the minimum sample S9. At this time, the maximum / minimum sample detection unit 11 detects sample S6 as the maximum sample. The waveform shown in Figure 6 is an example of a waveform in which there is a first consecutive sample in which two or more samples with the same value as the maximum sample (in this case, sample S6) are consecutive, including the maximum sample.

[0040] If the maximum / minimum sample correction unit 12 were not provided, the sample count detection unit 13 would detect that there is a 6-sample interval (6fs) between the minimum sample S0 and the maximum sample S6, and a 3-sample interval (3fs) between the maximum sample S6 and the minimum sample S9. In other words, the sample count detection unit 13 would detect that there are 6 samples between the minimum sample S0 and the maximum sample S6, and 3 samples between the maximum sample S6 and the minimum sample S9.

[0041] In the waveform including the first consecutive samples shown in Figure 6, sample S6, which was determined to be the sample with the maximum value, is likely not the sample with the true maximum value, but rather one of the other samples in the first consecutive samples that has the true maximum value. Therefore, the maximum / minimum sample correction unit 12 corrects the maximum sample as follows.

[0042] Figure 7 conceptually illustrates the correction operation of the maximum sample by the maximum / minimum sample correction unit 12. As shown in Figure 7, the maximum / minimum sample correction unit 12 sets a first straight line SL1 connecting the first sample S3 in the first sequence of samples and the sample immediately preceding it, S2. The maximum / minimum sample correction unit 12 also sets a second straight line SL2 connecting the last sample in the first sequence of samples, sample S6, which is detected as the maximum sample by the maximum / minimum sample detection unit 11, and the sample immediately following it, S7.

[0043] The maximal / minimal sample correction unit 12 sets an estimated maximum sample SmaxE, which is estimated to have the true maximum value, at the intersection of the first straight line SL1 and the second straight line SL2. The maximal / minimal sample correction unit 12 considers the sample closest to the projection point PpE obtained by projecting the estimated maximum sample SmaxE onto the flat waveform of the first continuous sample as the sample with the true maximum value. Here, the maximal / minimal sample correction unit 12 considers sample S4 as the sample with the true maximum value and assigns a maximum sample tag to sample S4. Sample S4, to which the maximum sample tag has been assigned, becomes the corrected maximum sample. That is, the maximal / minimal sample correction unit 12 corrects the maximum sample from sample S6 to sample S4, which is the corrected maximum sample with the true maximum value.

[0044] Depending on the slope of the first straight line SL1 and the second straight line SL2, a sample detected as a maximum sample by the maximum / minimum sample detection unit 11 may be considered as a sample with a true maximum value, and a maximum sample tag may be assigned to that sample.

[0045] In the extremely small samples S0 and S9 detected by the extremely large / extremely small sample detection unit 11, there are no consecutive samples with the same value. Therefore, the extremely large / extremely small sample correction unit 12 does not correct the extremely small samples S0 and S9, and extremely small sample tags are assigned to the extremely small samples S0 and S9. Accordingly, the sample number detection unit 13 detects the number of samples between the extremely small sample S0, which has been assigned an extremely small sample tag, and the sample S4, which has been assigned an extremely large sample tag, which are adjacent to each other, and the number of samples between the sample S4, which has been assigned an extremely large sample tag, and the extremely small sample S9, which has been assigned an extremely small sample tag. Consequently, the sample number detection unit 13 detects that there is a 4-sample interval (4fs) between the extremely small sample S0 and the sample S4, and a 5-sample interval (5fs) between the sample S4 and the extremely small sample S9. In other words, the sample number detection unit 13 detects that there are 4 samples between the extremely small sample S0 and the sample S4, and 5 samples between the sample S4 and the extremely small sample S9.

[0046] Figure 8 shows the corrected waveform obtained by adding or subtracting a correction value to the waveform obtained by the addition / subtraction unit 16 and the maximum / minimum sample correction unit 12, as shown in Figure 7, where the maximum sample was corrected from sample S6 to sample S4. Since sample S3, which precedes sample S4, and sample S5, which follows, have the same value as sample S4, the difference value calculated by the difference value calculation unit 14 becomes 0, and the correction value Vadd is not added to samples S3 and S5. The correction value Vsub is subtracted from samples S1 and S8.

[0047] Assume that the addition / subtraction unit 16 is configured to perform the addition / subtraction processing shown in Figures 5A and 5B if the sample interval is 6 samples or more. Assume that the waveform shown in Figure 6 is processed by the addition / subtraction unit 16 with the sample S6 detected by the maximum / minimum sample detection unit 11 remaining as the maximum sample. Then, the following operations will be performed: subtraction of the correction value Vsub for samples S1 and S2, addition of the correction value Vadd for sample S7, and subtraction of the correction value Vsub for sample S8.

[0048] As described above, in the waveform shown in Figure 6, sample S6 is not the sample with the true maximum value, while sample S4 is the sample with the true maximum value. The digital audio processing device 100 is equipped with a maximum / minimum sample correction unit 12, which enables it to perform addition and subtraction processing as shown in Figure 8. According to the digital audio processing device 100, even if the audio signal contains a waveform in which multiple samples have the same value as the maximum sample, the sample interval can be detected more accurately, and an ideal harmonic signal for improving sound quality can be generated. Verification by the inventors has confirmed that the perceived sound quality is improved.

[0049] Furthermore, the operation of the digital audio processing device 100 when the audio signal input to the digital audio processing device 100 includes the waveform shown in Figure 9 will be explained. As shown in Figure 9, the sample values ​​decrease sequentially from the maximum sample S20 to sample S23, and samples with the same value are consecutive from sample S23 to sample S26. The sample values ​​increase sequentially from sample S26 to the maximum sample S29. At this time, the maximum / minimum sample detection unit 11 detects sample S26 as the minimum sample. The waveform shown in Figure 9 is an example of a waveform in which there is a second consecutive sample in which two or more samples with the same value as the minimum sample (in this case, sample S26) are consecutive, including the minimum sample.

[0050] If the maximum / minimum sample correction unit 12 were not provided, the sample count detection unit 13 would detect that there is a 6-sample interval (6fs) between the maximum sample S20 and the minimum sample S26, and a 3-sample interval (3fs) between the minimum sample S26 and the maximum sample S29. In other words, the sample count detection unit 13 would detect that there are 6 samples between the maximum sample S20 and the minimum sample S26, and 3 samples between the minimum sample S26 and the maximum sample S29.

[0051] In the waveform including the second series of samples shown in Figure 9, sample S26, which was determined to be the sample with a local minimum, is not the sample with the true local minimum, and it is highly likely that one of the samples in the second series of samples other than sample S26 is the sample with the true local minimum. Therefore, the maximum / minimum sample correction unit 12 corrects the minimum sample as follows.

[0052] Figure 10 conceptually illustrates the correction operation of the minimum sample by the maximum / minimum sample correction unit 12. As shown in Figure 10, the maximum / minimum sample correction unit 12 sets a third straight line SL11 connecting the first sample S23 in the second sequence of samples and the sample immediately preceding it, S22. The maximum / minimum sample correction unit 12 also sets a fourth straight line SL12 connecting the last sample in the second sequence of samples, sample S26, which is detected as a minimum sample by the maximum / minimum sample detection unit 11, and the sample immediately following it, S27.

[0053] The maximal / minimal sample correction unit 12 sets an estimated minimum sample SminE, which is estimated to have the true minimum, at the intersection of the third straight line SL11 and the fourth straight line SL12. The maximal / minimal sample correction unit 12 considers the sample closest to the projection point PpE obtained by projecting the estimated minimum sample SminE onto the flat waveform of the second continuous sample as the sample with the true minimum. Here, the maximal / minimal sample correction unit 12 considers sample S24 as the sample with the true minimum and assigns a minimum sample tag to sample S24. Sample S24, to which the minimum sample tag has been assigned, becomes the corrected minimum sample. That is, the maximal / minimal sample correction unit 12 corrects the minimum sample from sample S26 to sample S24, which is the corrected minimum sample with the true minimum.

[0054] Depending on the slope of the third straight line SL11 and the fourth straight line SL12, a sample detected as a minimum sample by the maximum / minimum sample detection unit 11 may be considered as a sample with a true minimum value, and a minimum sample tag may be assigned to that sample.

[0055] In the maximum samples S20 and S29 detected by the maximum / minimum sample detection unit 11, there are no consecutive samples with the same value. Therefore, the maximum / minimum sample correction unit 12 does not correct the maximum samples S20 and S29, and maximum sample tags are assigned to the maximum samples S20 and S29. Accordingly, the sample number detection unit 13 detects the number of samples between the adjacent maximum sample S20, which has been assigned a maximum sample tag, and sample S24, which has been assigned a minimum sample tag, and the number of samples between sample S24, which has been assigned a minimum sample tag, and maximum sample S29, which has been assigned a maximum sample tag. Consequently, the sample number detection unit 13 detects that there is a 4-sample interval (4fs) between the maximum sample S20 and sample S24, and a 5-sample interval (5fs) between sample S24 and maximum sample S29. In other words, the sample count detection unit 13 detects that the number of samples between the maximum sample S20 and sample S24 is 4, and the number of samples between sample S24 and the maximum sample S9 is 5.

[0056] Figure 11 shows the corrected waveform obtained by adding or subtracting a correction value to the waveform obtained by the addition / subtraction unit 16 and the maximum / minimum sample correction unit 12, which corrects the minimum sample from sample S26 to sample S24 as shown in Figure 10. Since the sample S23 immediately preceding sample S24 and the sample S25 immediately following sample S24 have the same value as sample S24, the difference value calculated by the difference value calculation unit 14 becomes 0, and the correction value Vsub is not subtracted from samples S23 and S25. The correction value Vadd is added to samples S21 and S28.

[0057] Assume that the addition / subtraction unit 16 is configured to perform the addition / subtraction processing shown in Figures 5A and 5B if the sample interval is 6 samples or more. Assume that the waveform shown in Figure 9 is processed by the addition / subtraction unit 16 with the sample S26 detected by the maximum / minimum sample detection unit 11 remaining as the minimum sample. Then, the correction value Vadd will be added to samples S21 and S22, the correction value Vsub will be subtracted from sample S27, and the correction value Vadd will be added to sample S28.

[0058] As described above, in the waveform shown in Figure 9, sample S26 is not the sample with the true minimum value, but rather sample S24 is the sample with the true minimum value. The digital audio processing device 100 is equipped with a maximum / minimum sample correction unit 12, which enables it to perform addition and subtraction processing as shown in Figure 11. According to the digital audio processing device 100, even if the audio signal contains a waveform in which multiple consecutive samples have the same value as the minimum sample, the sample interval can be detected more accurately, and an ideal harmonic signal for improving sound quality can be generated. Verification by the inventors has confirmed that the perceived sound quality is improved.

[0059] While Figures 7 and 10 conceptually explain the correction operation of maximum and minimum samples by the maximum / minimum sample correction unit 12, the samples to which maximum sample tags should be assigned and the samples to which minimum sample tags should be assigned can be calculated as shown in Figures 12 and 13.

[0060] Figure 12 shows the same waveform as Figure 6. In Figure 12, the x-axis is defined as the axis passing through the flat waveform of the first series of samples, the y-axis is defined as the axis passing through the first sample S3 of the flat waveform and perpendicular to the x-axis, and a two-dimensional coordinate system is set with sample S3 as the origin at coordinate (x0, y0). The coordinates of sample S2 are (x(-1), y(-1)), the coordinates of sample S6 are (x3, y3), and the coordinates of sample S7 are (x4, y4). In this way, each sample of the waveform shown in Figure 6 can be represented by xy coordinates on the x and y axes.

[0061] The slope of the first line SL1 is d3, and since the first line SL1 passes through the origin, the first line SL1 can be expressed by the following equation (1). The slope of the second line SL2 is (-d7), and since it passes through the coordinates (x3, y3), the second line SL2 can be expressed by the following equation (2). The sign * indicates multiplication. y = d³ * x …(1) y = (-d7)*x + (d7*x3) …(2)

[0062] The x-component of the estimated maximum sample SmaxE, which is the intersection point of the first line SL1 and the second line SL2, can be obtained by equation (3). SmaxE = (d7*x3) / (d3+d7) …(3)

[0063] If we let Se be the sample closest to the projection point PpE obtained by projecting the estimated maximum sample SmaxE onto a flat waveform, then sample Se can be obtained using equation (4). The projection point PpE is the x-component of the estimated maximum sample SmaxE calculated in equation (3). In equation (4), FL is the length of the flat waveform (sample interval), which is 3 here. (int) is a function that rounds down decimals to integers. By substituting FL for x3 in equation (3), and adding 0.5 to the result of the division (d7*FL) / (d3+d7) and then rounding down the decimal, the coordinates representing the sample are rounded, and we can obtain the coordinates of sample Se that is closest to the projection point PpE. In equation (4), d3 and d7 are absolute values. Here, sample S4 is obtained as sample Se. Se=(int)[(d7*FL) / (d3+d7)+0.5] …(4)

[0064] Figure 13 shows the same waveform as Figure 9. In Figure 13, the x-axis is defined as the axis passing through the flat waveform of the second series of samples, the y-axis is defined as the axis passing through the first sample S23 of the flat waveform and perpendicular to the x-axis, and a two-dimensional coordinate system is set with sample S23 as the origin (x0, y0). The coordinates of sample S22 are (x(-1), y(-1)), the coordinates of sample S26 are (x3, y3), and the coordinates of sample S27 are (x4, y4). In this way, each sample of the waveform shown in Figure 9 can be represented by xy coordinates on the x and y axes.

[0065] The slope of the third line SL11 is (-d23), and since the third line SL11 passes through the origin, the third line SL11 can be expressed by the following equation (5). The slope of the fourth line SL12 is d27, and since it passes through the coordinates (x3, y3), the fourth line SL12 can be expressed by the following equation (6). y = (-d23) * x …(5) y = d27*x + ((-d27)*x3) …(6)

[0066] The estimated minimum sample SminE, which is the intersection point of the third line SL11 and the fourth line SL12, can be calculated using equation (7). SmaxE=(d27*x3) / (d23+d27) …(7)

[0067] The sample Se closest to the projection point PpE obtained by projecting the estimated minimum sample SminE onto a flat waveform can be found using equation (8), similar to equation (4). In equation (8), d23 and d27 are absolute values. Here, sample S24 is obtained as sample Se. Se=(int)[(d27*FL) / (d23+d27)+0.5] …(8)

[0068] The operation of the digital audio processing device 100 and the digital audio processing methods performed by the digital audio processing device 100 will be further explained using the flowcharts shown in Figures 14 and 15. The flowcharts shown in Figures 14 and 15 also show the processes that the digital audio processing program causes the central processing unit of the microcomputer, which will be described later, to execute.

[0069] In Figure 14, when an audio signal is input to the digital audio processing device 100 and processing begins, the maximum / minimum sample detection unit 11 detects the maximum and minimum samples in step S31. The maximum / minimum sample correction unit 12 determines in step S32 whether there are consecutive samples with the same sample value as the maximum or minimum sample.

[0070] If, in step S32, consecutive samples have the same sample value as the maximum sample (YES), the maximum / minimum sample correction unit 12 assigns a maximum sample tag to a sample different from the detected maximum sample in step S33. If, in step S32, consecutive samples have the same sample value as the minimum sample (YES), the maximum / minimum sample correction unit 12 assigns a minimum sample tag to a sample different from the detected minimum sample in step S33. The process then proceeds to step S35.

[0071] If, in step S32, no consecutive samples have the same sample value as the maximum or minimum sample (NO), the maximum / minimum sample correction unit 12, in step S34, assigns a maximum sample tag to the detected maximum sample and a minimum sample tag to the detected minimum sample. The process then proceeds to step S35.

[0072] Figure 15 shows the specific processing in step S33. In Figure 15, the maximum / minimum sample correction unit 12 obtains the slope da of the straight line connecting the sample immediately preceding the flat waveform with the same value and the first sample of the flat waveform in step S331. The slope d3 shown in Figure 12 and the slope d23 shown in Figure 13 correspond to the slope da. In step S332, the maximum / minimum sample correction unit 12 obtains the slope db of the straight line connecting the last sample of the flat waveform and the sample immediately following the flat waveform. The slope d7 shown in Figure 12 and the slope d27 shown in Figure 13 correspond to the slope db. In step S333, the maximum / minimum sample correction unit 12 obtains the length FL of the flat waveform.

[0073] In step S334, the maximum / minimum sample correction unit 12 calculates the sample Se to which a maximum sample tag should be assigned and the sample Se to which a minimum sample tag should be assigned, based on the calculation formula shown in equation (9) below. Se=(int)[(db*FL) / (da+db)+0.5] …(9)

[0074] In step S335, the maximal / minimal sample correction unit 12 assigns a maximal sample tag or a minimal sample tag to the sample Se. In this way, the maximal or minimal sample in a flat waveform where samples of the same value are consecutive is corrected to a corrected maximal sample having a true maximal value or a corrected minimal sample having a true minimum value.

[0075] Returning to Figure 14, in step S35, the sample count detection unit 13 detects the number of samples (sample interval) between the sample with the maximum sample tag and the sample with the minimum sample tag. In step S36, the difference value calculation unit 14 calculates the difference value between adjacent samples. In step S37, the correction value calculation unit 15 calculates the correction value. In step S38, the addition / subtraction unit 16 adds or subtracts the correction value to the sample with the maximum sample tag and the samples near the sample with the minimum sample tag.

[0076] In step S39, the digital audio processing device 100 determines whether the input of the audio signal has ended. If the input of the audio signal has not ended (NO), the processing from step S31 onwards is repeated. If the input of the audio signal has ended, the digital audio processing device 100 terminates the processing.

[0077] The digital audio processing device 100 shown in Figure 1 can be realized by the execution of a digital audio processing program by the central processing unit of a microcomputer. In Figure 16, the central processing unit (hereinafter referred to as CPU) 50, the main memory 55, and the storage medium 60 are connected by a bus. The storage medium 60 is any non-temporary storage medium such as a hard disk drive, optical disc, or semiconductor memory. The digital audio processing program is stored in the storage medium 60. The digital audio processing program may be transmitted from an external server via a communication line such as the Internet and stored in the storage medium 60.

[0078] The CPU 50 loads the digital audio processing program stored in the storage medium 60 into the main memory 55. The CPU 50 executes the processes shown in Figures 14 and 15 by executing each instruction described in the digital audio processing program loaded into the main memory 55.

[0079] In the description of this embodiment, the maximum / minimum sample correction unit 12 performed a process of tagging the sample. However, if a first or second consecutive sample exists, the maximum / minimum sample detection unit 11 detects the maximum or minimum sample and the maximum / minimum sample correction unit 12 corrects it. This process does not necessarily have to involve tagging.

[0080] For example, in the maximum / minimum sample correction unit 12, if the maximum sample detected by the maximum / minimum sample detection unit 11 and the maximum sample of the maximum / minimum sample correction unit 12 are the same sample, the maximum sample detected by the maximum / minimum sample detection unit 11 will be overwritten with the same sample. Conversely, if the maximum sample detected by the maximum / minimum sample detection unit 11 and the maximum sample of the maximum / minimum sample correction unit 12 are different samples, the maximum sample detected by the maximum / minimum sample detection unit 11 will be overwritten with the different sample. The same applies to minimum samples.

[0081] As described above, in the digital audio processing device, digital audio processing method, and digital audio processing program according to one embodiment, the digital audio signal to be processed includes a waveform in which multiple samples with the same value as the maximum sample or minimum sample are consecutive. According to the digital audio processing device, digital audio processing method, and digital audio processing program according to one embodiment, the maximum sample or minimum sample is corrected to a corrected maximum sample or corrected minimum sample that is close to the true maximum sample or true minimum sample. Therefore, according to the digital audio processing device, digital audio processing method, and digital audio processing program according to one embodiment, it is possible to detect the sample interval more accurately and generate a harmonic signal that is ideal for improving sound quality.

[0082] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0083] 11. Extremely large and extremely small sample detection unit 12. Extremely large / extremely small sample correction section 13. Sample Count Detection Unit 14 Difference Value Calculation Unit 15 Correction Value Calculation Unit 16 Addition and Subtraction Section 50 Central Processing Unit 55 Main Memory 60 Storage medium 100 Digital audio processing devices

Claims

1. A maximum / minimum sample detection unit that detects the maximum and minimum samples in a series of samples that constitute an input digital audio signal, A maximum / minimum sample correction unit that, when there is a first consecutive sample consisting of two or more consecutive samples including the maximum sample that have the same value as the maximum sample detected by the maximum / minimum sample detection unit, assigns a maximum sample tag to a sample from the first consecutive sample that is different from the maximum sample; when there are no two or more consecutive samples including the maximum sample that have the same value as the maximum sample detected by the maximum / minimum sample detection unit, assigns a maximum sample tag to the maximum sample; when there is a second consecutive sample consisting of two or more consecutive samples including the minimum sample that have the same value as the minimum sample detected by the maximum / minimum sample detection unit, assigns a minimum sample tag to a sample from the second consecutive sample that is different from the minimum sample; and when there are no two or more consecutive samples including the minimum sample that have the same value as the minimum sample detected by the maximum / minimum sample detection unit, assigns a minimum sample tag to the minimum sample. A sample count detection unit that detects the number of samples between adjacent samples, one assigned the maximum sample tag and the other assigned the minimum sample tag. A difference value calculation unit that calculates the difference value of adjacent samples in the aforementioned series of samples, A correction value calculation unit calculates a correction value by multiplying the difference value calculated by the difference value calculation unit by a predetermined coefficient corresponding to the number of samples detected by the number of samples detection unit, An addition / subtraction unit adds the correction value calculated by the correction value calculation unit to at least the sample immediately preceding and immediately following the sample to which the maximum sample tag is attached, and subtracts the correction value calculated by the correction value calculation unit from at least the sample immediately preceding and immediately following the sample to which the minimum sample tag is attached. A digital audio processing device equipped with the following features.

2. The aforementioned maximum / minimum sample correction unit is: An estimated maximum sample is set at the intersection of a first straight line connecting the first sample in the first consecutive sample and the sample immediately preceding it, and a second straight line connecting the last sample in the first consecutive sample and the sample immediately following it. Among the first consecutive samples, the sample closest to the projection point obtained by projecting the estimated maximum sample onto the flat waveform of the first consecutive samples is given the maximum sample tag. An estimated minimum sample is set at the intersection of a third line connecting the first sample in the second consecutive sample and the sample immediately preceding it, and a fourth line connecting the last sample in the second consecutive sample and the sample immediately following it. Among the second series of samples, the sample closest to the projection point obtained by projecting the estimated minimum sample onto the flat waveform of the second series of samples is assigned the minimum sample tag. The digital audio processing device according to claim 1.

3. The system detects the maximum and minimum samples in a series of samples that make up the input digital audio signal. When there is a first sequence of two or more consecutive samples, including the maximum sample, that have the same value as the detected maximum sample, the maximum sample tag is assigned to a sample from the first sequence that is different from the maximum sample. When there are no two or more consecutive samples with the same value as the detected maximum sample, including the maximum sample, a maximum sample tag is assigned to the maximum sample. When there is a second sequence of two or more consecutive samples, including the minimum sample, that have the same value as the detected minimum sample, the minimum sample tag is assigned to a sample from the second sequence that is different from the minimum sample. When no two or more consecutive samples with the same value as the detected minimum sample, including the minimum sample, are found, a minimum sample tag is assigned to the minimum sample. The number of samples between adjacent samples, one with the maximum sample tag and the other with the minimum sample tag, is detected. The difference value of adjacent samples in the aforementioned series of samples is calculated, The calculated difference value is multiplied by a predetermined coefficient corresponding to the number of detected samples to calculate a correction value. Of the series of samples, the correction value is added to at least the sample immediately preceding and immediately following the sample to which the maximum sample tag is attached, and the correction value is subtracted from at least the sample immediately preceding and immediately following the sample to which the minimum sample tag is attached. Digital audio processing method.

4. On the computer, A step of detecting the maximum and minimum samples in a series of samples that constitute an input digital audio signal, When there is a first sequence of two or more consecutive samples, including the maximum sample, that have the same value as the detected maximum sample, the step of assigning a maximum sample tag to a sample that is different from the maximum sample from the first sequence of samples, When there are no two or more consecutive samples with the same value as the detected maximum sample, including the maximum sample, the step of assigning a maximum sample tag to the maximum sample, When there is a second sequence of two or more consecutive samples, including the minimum sample, that have the same value as the detected minimum sample, the minimum sample tag is assigned to a sample that is different from the minimum sample from the second sequence of samples. When no two or more consecutive samples with the same value as the detected minimum sample, including the minimum sample, are found, the minimum sample is tagged with a minimum sample tag. A step of detecting the number of samples between adjacent samples that have been assigned the maximum sample tag and samples that have been assigned the minimum sample tag, The steps include: calculating the difference value of adjacent samples in the aforementioned series of samples; The steps include: calculating a correction value by multiplying the calculated difference value by a predetermined coefficient corresponding to the number of detected samples; The steps include adding the correction value to at least the sample immediately preceding and immediately following the sample to which the maximum sample tag is attached, and subtracting the correction value from at least the sample immediately preceding and immediately following the sample to which the minimum sample tag is attached, A digital audio processing program that performs this operation.

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