JP5023794B2 - Digital audio processing apparatus and digital audio processing program - Google Patents

Description

  The present invention corrects a digital audio signal by adding a variable amount corresponding to a difference value between adjacent samples in the digital audio signal to the maximum value side sample and subtracting it from the minimum value side sample. The present invention relates to a digital audio processing apparatus and a digital audio processing program.

  For example, in the CD standard, an analog audio signal is converted into a digital audio signal with a sampling frequency fs = 44.1 kHz and a quantization bit number = 16 bits, and is cut up to a band of 22.05 kHz according to the sampling theorem. Also, in the DVD video standard and the DVD audio standard, sampling frequencies fs = 48 kHz, 96 kHz, 192 kHz, the number of quantization bits = 24 bits, etc. higher than 44.1 kHz are used in order to obtain a richer presence than the CD signal. Has been.

  However, even if an existing CD signal is directly converted from 16 to 24 bits and converted to 48 kHz or the like by high-sampling for the purpose of obtaining a sense of reality, a band of 22.05 kHz or more is not generated. For this reason, a method has been proposed in which a high frequency band obtained by shaping the waveform of a CD signal is added to the original signal to reproduce a rich sense of reality. For example, as the first prior art, in Patent Document 1 below, the sampling data before and after are compared to detect the maximum value and the minimum value of the sampling data, and from the maximum value to the minimum value, from the minimum value to the maximum value. The number of samples is detected, and the difference from the previous sample is calculated for each sample excluding the local maximum value and local minimum value, and this is multiplied by the coefficient corresponding to the number of samples described above. Addition processing is performed on samples that are close to the maximum value except for subtraction, and subtraction processing is performed on samples that are close to the minimum value excluding the minimum value.

  In addition, as the second conventional technique, in Patent Document 2 below, the maximum value and the minimum value are also applied, and a predetermined coefficient is set for the difference between the maximum value and the minimum value and the value one sample before. Multiplication is performed, and the multiplication result is subjected to addition processing for the maximum value, and subtraction processing is performed for the minimum value. By these methods, it is possible to obtain a reproduction sound that is as sharp as an original analog signal, and has reality and clarity.

FIG. 2 is a block diagram related to a conventional digital audio processing apparatus in Patent Document 2. In FIG. Here, as an example, an input / output audio signal is set to fs = 96 kHz and the number of quantization bits = 24 bits. The extreme value calculation means 11 compares the input audio signal with the previous sample for each sample, detects whether it is large, small, or equal, and detects the maximum and minimum values of the waveform. The sample number detection means 12 detects the number of samples included between the obtained maximum value and minimum value. The difference value calculation means 13 obtains a difference value Δ between each sample including the maximum value and the minimum value and the value one sample before. The variable amount calculation means 14 calculates the variable amount = Δ × α by multiplying the obtained difference value Δ by each coefficient α corresponding to the number of samples included. The addition / subtraction means 15 performs a process of adding a variable amount = Δ × α for a sample close to a maximum value including a maximum value, and a variable amount = Δ for a sample close to a minimum value including a minimum value. The process of subtracting xα is performed.
Japanese Patent No. 3401171 (Claim 1) Japanese Patent No. 3659489 (Claim 1)

  However, according to the first and second conventional techniques, it is possible to convert audio information in a narrow frequency band into audio information in a wide frequency band with a small, simple and inexpensive circuit configuration, and the purpose can be achieved. , For each sample, calculate the difference Δ from the previous sample, multiply this by the coefficient α according to the number of samples, this multiplication result = Δ × α is added to the maximum value side sample, Since the subtraction process is performed on the sample on the minimum value side, the addition value / subtraction value differs from sample to sample, so the signal power of the original data may be changed. That is, when the total power obtained by the sum of squares of the added value and the total power obtained by the sum of the squares of the subtracted values do not coincide with each other, it is perceived that the volume level is changed.

  FIG. 3 is a diagram for explaining the conventional waveform processing and shows an example. In this figure, there are three samples of the interval between the minimum value and the maximum value in the sampling period, and variable amounts = Δd1 and Δd3 are added to the samples X2 and X4 close to the maximum value X3, respectively, and the minimum values X0 and X6 are respectively added. Variables = Δd2 and Δd4 are subtracted from near samples X1 and X5. In this example, in the case of Δd3 and Δd4, since the difference value between the samples X3-X4 and X5-X6 is uniform, Δd3 = Δd4, whereas in the case of Δd1 and Δd2, the audio signal is abrupt. Since a rise is observed, an inconsistent state occurs such that Δd2> Δd1. Therefore, when the subtraction process for Δd2 is performed, the power for the square of (Δd2−Δd1) decreases.

  Therefore, in the present invention, a digital audio signal is added by adding a variable amount corresponding to a difference value between adjacent samples before and after in the digital audio signal to the maximum value side sample and subtracting from the minimum value side sample. An object of the present invention is to provide a digital audio processing apparatus and a digital audio processing program capable of correcting a digital audio signal so that the volume level does not change when correcting.

In order to achieve the above object, the digital audio processing apparatus of the present invention is an extreme value calculating means for obtaining a maximum value and a minimum value by comparing samples before and after temporally adjacent in the original digital audio information,
Sample number detection means for detecting the number of samples from the maximum value to the minimum value and the number of samples from the minimum value to the maximum value;
A difference value calculating means for obtaining a difference between each sample including the maximum value and the minimum value and a value one sample before;
A first variable amount for multiplying each coefficient corresponding to the number of samples by each difference value and adding to the maximum value side sample, and a second variable amount for subtracting from the minimum value side sample Variable amount calculating means for obtaining a variable amount of
A power calculating means for calculating the power amount of power amount and a second variable amount of the first variable amount calculated by the variable amount calculating means,
A variable for correcting the first variable amount and the second variable amount so that the total power amount of the first variable amount and the total power amount of the second variable amount calculated by the power calculation means are the same. An amount correction means;
The first variable amount corrected by the variable amount correction unit is added to the maximum value side sample, and the second variable amount corrected by the variable amount correction unit is subtracted from the minimum value side sample. Adding and subtracting means to
Have.

In order to achieve the above object, the digital audio processing program of the present invention calculates an extreme value by calculating a maximum value and a minimum value by comparing samples before and after temporally adjacent in the original digital audio information,
A sample number detection step for detecting the number of samples from the maximum value to the minimum value and the number of samples from the minimum value to the maximum value;
A difference value calculating step for obtaining a difference between each sample including the maximum value and the minimum value and a value one sample before;
A first variable amount for multiplying each coefficient corresponding to the number of samples by each difference value and adding to the maximum value side sample, and a second variable amount for subtracting from the minimum value side sample A variable amount calculating step for obtaining a variable amount of
A power calculating step of calculating the power amount of power amount and a second variable amount of the first variable amount calculated by the variable-amount calculating step,
A variable that corrects the first variable amount and the second variable amount so that the total power amount of the first variable amount and the total power amount of the second variable amount calculated in the power calculation step are the same. An amount correction step;
The first variable amount corrected in the variable amount correction step is added to the sample on the maximum value side, and the second variable amount corrected in the variable amount correction step is subtracted from the sample on the minimum value side. Adding and subtracting step,
Have.

  According to the present invention, the first variable amount power to be added to the local maximum side sample and the second variable amount power to be subtracted from the local minimum side sample are the same. , The second variable amount is corrected, and each is added to the sample on the maximum value side and subtracted from the minimum value side, so that the signal power between the minimum value and the maximum value and between the maximum value and the minimum value is Since the signal power is maintained, the digital audio signal can be corrected so that the volume level does not change.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a digital audio processing apparatus and a digital audio processing program according to the present invention. Compared to the conventional block diagram (FIG. 2), a power calculation unit 26 and a variable amount correction unit 27 are added between the variable amount calculation unit 14 and the addition / subtraction unit 15. In the power calculation unit 26, among the variable amounts obtained by the variable amount calculation unit 14, the total power amount obtained by the square sum of the variable amount (addition value) used for addition and the square of the variable amount (subtraction value) used for subtraction. Calculate the total amount of power determined by the sum. In the variable amount correction means 27, by comparing the total power of the added value and the total power of the subtracted value, the compensation coefficient of the added value and the subtracted value is calculated so that each power becomes the same, and the added value or the subtracted value is calculated as the compensation coefficient. To correct.

Hereinafter, the power calculating unit 26 and the variable amount correcting unit 27 will be described in detail using the example (Δd2> Δd1) of FIG. In the power calculation means 26, the total power (Plus_pw) of the addition value and the total power (Minus_pw) of the subtraction value are obtained. In the example of FIG. 3, the following equations 1 and 2 are obtained.
Plus_pw = (Δd1) ² (Formula 1)
Minus_pw = (Δd2) ² (Formula 2)

  The variable amount correction means 27 calculates a compensation coefficient for adjusting to the larger total power amount so that Plus_pw = Minus_pw. Assuming that the compensation coefficient for the added value is ratio_p and the compensation coefficient for the subtraction value is ratio_m, the following equations 3 and 4 are obtained.

  ratio_m = 1 (Formula 4)

Then, the addition value and the subtraction value are corrected using the compensation coefficients (ratio_p, ratio_m).
Δd1 ′ = (ratio_p × Δd1) → Δd1 (Formula 5)
Δd2 ′ = (ratio_m × Δd2) → Δd2 (Formula 6)
Based on the above, let us consider deriving a general formula. There are m addition values (i = 0 to m−1), each defined as ΔPi, n subtraction values (j = 0 to n−1), and each defined as ΔMj.

Similarly to the above, it is considered to calculate a compensation coefficient for adjusting to the larger power total amount so that Plus_pw = Minus_pw. When the compensation coefficient for the added value is ratio_p and the compensation coefficient for the subtracted value is ratio_m, the following is obtained.
(When Plus_pw> Minus_pw)
ratio_p = 1 (Formula 9)

 (If Plus_pw <Minus_pw)

ratio_m = 1 (Formula 12)
(When Plus_pw = Minus_pw)
ratio_p = ratio_m = 1 (Formula 13)
From the above, assuming that the addition value corrected using the compensation coefficient is ΔP′i and the subtraction value is ΔM′j, the calculation is performed as follows.
ΔP′i = (ratio_p × ΔPi) (Formula 14)
ΔM′j = (ratio_m × ΔMj) (Formula 15)

  In the example shown above, it is considered to calculate the compensation coefficient for adjusting to the larger power total amount so that Plus_pw = Minus_pw, but it is also possible to adjust to the smaller power total amount side.

Further, the addition value and the subtraction value corrected by the variable amount correction unit 27 are smaller than the difference value used when the variable amount calculation unit 14 calculates the variable amount used for addition and subtraction, respectively. Limits may be added. That is, assuming that the difference value used when calculating the variable amount used for addition is DPi, and the difference value used when calculating the variable amount used for subtraction is DMj, (Equation 14) and (Equation 15) On the other hand, the following expressions 16 and 17 may be added.
| ΔP′i | <| DPi | (Formula 16)
| ΔM′j | <| DMj | (Formula 17)

  In the example shown above, the input audio signal is set to fs = 96 kHz and the number of quantization bits = 24 bits, but fs = 44.1 kHz and the number of quantization bits = 16 bits conforming to the CD standard may be used. . Further, the audio signal is not limited to the linear PCM signal, but may be a signal resulting from encoding / decoding processing by MP3, AAC encoding method, or the like.

It is a block diagram which shows one Embodiment of the digital audio processing apparatus and digital audio processing program which concern on this invention. It is a block diagram which shows the conventional digital audio processing apparatus. It is a figure for demonstrating the waveform process in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Extreme value calculation means 12 Sample number detection means 13 Difference value calculation means 14 Variable amount calculation means 15 Addition / subtraction means 26 Power calculation means 27 Variable amount correction means

Claims (4)

An extreme value calculation means for obtaining a local maximum value and a local minimum value by comparing samples before and after temporally adjacent in the original digital audio information;
Sample number detection means for detecting the number of samples from the maximum value to the minimum value and the number of samples from the minimum value to the maximum value;
A difference value calculating means for obtaining a difference between each sample including the maximum value and the minimum value and a value one sample before;
A first variable amount for multiplying each coefficient corresponding to the number of samples by each difference value and adding to the maximum value side sample, and a second variable amount for subtracting from the minimum value side sample Variable amount calculating means for obtaining a variable amount of
A power calculating means for calculating the power amount of power amount and a second variable amount of the first variable amount calculated by the variable amount calculating means,
A variable for correcting the first variable amount and the second variable amount so that the total power amount of the first variable amount and the total power amount of the second variable amount calculated by the power calculation means are the same. An amount correction means;
The first variable amount corrected by the variable amount correction unit is added to the maximum value side sample, and the second variable amount corrected by the variable amount correction unit is subtracted from the minimum value side sample. Adding and subtracting means to
A digital audio processing apparatus.   2. The first and second variable amounts corrected by the variable amount correcting unit are values smaller than the respective difference values calculated by the difference value calculating unit. Digital audio processor. An extreme value calculation step for obtaining a local maximum value and a local minimum value by comparing samples before and after temporally adjacent in the original digital audio information;
A sample number detection step for detecting the number of samples from the maximum value to the minimum value and the number of samples from the minimum value to the maximum value;
A difference value calculating step for obtaining a difference between each sample including the maximum value and the minimum value and a value one sample before;
A first variable amount for multiplying each coefficient corresponding to the number of samples by each difference value and adding to the maximum value side sample, and a second variable amount for subtracting from the minimum value side sample A variable amount calculating step for obtaining a variable amount of
A power calculating step of calculating the power amount of power amount and a second variable amount of the first variable amount calculated by the variable-amount calculating step,
A variable that corrects the first variable amount and the second variable amount so that the total power amount of the first variable amount and the total power amount of the second variable amount calculated in the power calculation step are the same. An amount correction step;
The first variable amount corrected in the variable amount correction step is added to the sample on the maximum value side, and the second variable amount corrected in the variable amount correction step is subtracted from the sample on the minimum value side. Adding and subtracting step,
A digital voice processing program.   The first and second variable amounts corrected by the variable amount correcting step are values smaller than the respective difference values calculated by the difference value calculating step. Digital audio processing program.

Images