JPH10322204A - Method and device for reducing distortion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce distortion at a specific level range in a digital audio signal by using a smoothed digital audio signal for a distortion presence part of the digital audio signal, a distorted digital audio signal for a part other than the distortion presence part and summing both sets of waveform. SOLUTION: A distortion presence part discrimination means 102 discriminates a part of a received digital audio signal at a specific level range of which data are in existence to be a distortion presence part and generates a switching reference signal. A waveform smoothing means 105 smoothes the received digital audio signal and provides an output of the result. A waveform synthesis means 106 generates cross fade coefficients A, B based on the switching reference signal from the distortion presence part discrimination means 102, multiplies the cross fade coefficient A with the smoothed digital audio signal by the waveform smoothing means 105, and multiplies the cross fade coefficient B with the digital audio signal from a delay means 104 of the distortion reduction device 101 and sums the digital audio signals with which the coefficierxts are multiplied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an apparatus and a method for reducing distortion in a digital audio signal.

[0002]

2. Description of the Related Art When digitally recording an audio signal, analog / digital (A / D: Analog / Digital) is used.
An analog audio signal is converted to a digital audio signal using a converter. When a digital audio signal is reproduced, digital / analog (D / A: Di)
The digital audio signal is converted to an analog audio signal using a gital / Analog) converter. Among digital recordings, PCM (Puls
e Code Modulation) In recording, the time axis direction of an analog audio signal is subdivided (sampling: sampling) at a certain frequency, and the signal level of each subdivided sample is represented by a certain bit length (quantization: (Quantization).

At the beginning of PCM recording, a 13-bit or 14-bit successive approximation A / D converter, which is lower than the current one, was mainly used. Also,
A / D converters in the early days of PCM recording have poorer linearity in A / D conversion characteristics than current A / D converters.
The digital audio signal contained many nonlinear errors, and the recorded digital audio signal also had many distortions.

[0004] The digital audio signals of the past having such distortions are some of those recording sources that are excellent in performance and those that are valuable in music history. There is a demand to correct such distortion and reproduce the 16-bit digital audio signal currently used in compact disks (CD: Compact Disk), digital audio tapes (DAT: Digital Audio Tape), and the like.

[0005]

As one of the methods for correcting the non-linear error of the past digital audio signal as described above, a conversion characteristic of an A / D converter used at the time of recording is measured and inversely corrected. Although a method is conceivable, the A / D converter used at the time of recording often does not exist at present, and the characteristics of the A / D converter change with time even if it is present, and based on the current characteristics, It is impossible to correct the non-linear error during recording by using
It is difficult to actually measure a / D converter to correct a nonlinear error of a past PCM recording source (digital audio signal).

[0006] Non-linear errors occur due to non-uniformity of each quantization step in an A / D converter with poor bit precision. When a digital audio signal having a non-linear error is reproduced by a D / A converter having good linearity, the reproduced signal is
Although it has a certain level of quantization noise corresponding to the number of data bits, by correcting this non-linear error, a certain level of quantization distortion may be increased. This distortion appears remarkably in the zero-cross portion where the nonlinear error is large, and has a drawback that it becomes a zero-cross distortion and the sound is jarring to the sense of hearing.

[0007] Since the zero-cross distortion is obtained by locally amplifying the quantization distortion in the zero-cross part as described above, the conventional quantization noise reduction method (smoothing by adaptive filter and waveform conversion) is used. ) Can be used, but since the quantization distortion of this zero-cross portion is enlarged compared to the quantization distortion of the other portions, if a process that can sufficiently correct this is performed, There is also a possibility that harmonic components of other parts of the music signal are lost, resulting in a change in sound quality due to deterioration of frequency characteristics.

Accordingly, an object of the present invention is to provide a distortion reduction method and a distortion reduction apparatus capable of reducing distortion of a digital audio signal generated in a specific level range.

[0009]

Therefore, according to the present invention, in a distortion reduction apparatus for reducing distortion of a digital audio signal, a range of a specific level where the distortion of the digital audio signal exists is defined as a distortion existence section. A distortion existence section discriminating means for detecting and generating a switching reference signal, a waveform smoothing means for smoothing the distortion of the digital audio signal, and a distortion existence section corresponding to the switching reference signal from the distortion existence section discriminating means. The digital audio signal obtained by continuously connecting the waveforms by cross-fading using the waveform of the digital audio signal from the waveform smoothing means during the And a waveform synthesizing means for outputting the same.

According to a second aspect of the present invention, there is provided a distortion reducing method for reducing distortion of a digital audio signal, wherein a range of a specific level where the distortion of the digital audio signal exists is detected as a distortion existing portion, and a switching reference signal is detected. Generates and smooths the distortion of the digital audio signal, and uses the waveform of the smoothed digital audio signal in the period corresponding to the distortion existing portion based on the switching reference signal, and uses the original digital signal in the period other than the distortion existing portion. It is characterized by using a waveform of an audio signal to output a digital audio signal whose waveform is continuously connected by cross-fading.

According to a third aspect of the present invention, there is provided a distortion reducing apparatus for reducing zero cross distortion caused by correcting a non-linear error of a digital audio signal having a non-linear error. A zero-crossing part discriminating means for detecting a portion where data exists in a range of ± 1 LSB as a zero-crossing part and generating a switching reference signal; a waveform smoothing means for smoothing the digital audio signal after the nonlinear error correction; Based on the switching reference signal from the zero-cross discriminating means, the waveform of the digital audio signal from the waveform smoothing means is used during the period corresponding to the zero-cross part, and the digital signal after the non-linear error correction is used during the period other than the zero-cross part. Using a waveform of an audio signal to output a digital audio signal whose waveform is continuously linked by fade It is characterized by comprising a waveform synthesis means.

According to a fourth aspect of the present invention, there is provided a distortion reducing method for reducing zero cross distortion caused by correcting a non-linear error of a digital audio signal having a non-linear error. A switching reference signal is generated by detecting a portion where data exists in a range of ± 1 LSB as a zero-crossing portion, and the digital audio signal after the non-linear error correction is smoothed. The digital audio signal whose waveform is continuously connected by crossfading is used by using the waveform of the digital audio signal smoothed during the period, and by using the waveform of the digital audio signal after the nonlinear error correction during the period other than the zero crossing part. It is characterized by outputting.

According to the present invention, a range of a specific level in which a distortion of a digital audio signal exists is detected as a distortion existence part, a switching reference signal is generated, and the digital audio signal is subjected to the distortion existence part using an adaptive filter or the like. Based on the switching reference signal, the waveform of the digital audio signal from the waveform smoothing unit is used in a period corresponding to the distortion existing portion based on the switching reference signal, and the waveform of the original digital audio signal is used in a period other than the distortion existing portion. In addition, since the waveforms are continuously connected by cross-fading, a digital audio signal with reduced distortion at a specific level can be obtained.

A switching reference signal is generated by detecting, from the digital audio signal before the non-linear error correction, a portion where data exists within a range of ± 1 LSB as a zero cross portion,
The digital audio signal in which zero cross distortion has occurred due to the nonlinear error correction is smoothed using an adaptive filter or the like, and the waveform of the smoothed digital audio signal (non-linear waveform) in the period corresponding to the zero cross part based on the switching reference signal. The waveform of the digital audio signal whose error has been corrected and smoothed) is used, and the waveform of the digital audio signal whose nonlinear error distortion has been corrected (the waveform of the digital audio signal having zero cross distortion) is used during periods other than the zero cross. Since the waveforms are continuously connected by fading, a digital audio signal with reduced zero cross distortion can be obtained.

[0017]

FIG. 1 is a schematic diagram showing a schematic configuration of an embodiment of a distortion reduction apparatus according to the present invention. In FIG. 1, a distortion reduction device 101 includes
02, delay means 103 and 104, and waveform smoothing means 1
05 and a waveform synthesizing unit 106.

The distortion existence section discriminating means 102 discriminates a portion where data exists in a specific level range of the input digital audio signal as a distortion existence section, and a waveform synthesizing section 106 described later converts the digital audio signal of the distortion existence section into a digital signal. A switching reference signal for synthesizing the waveform and the waveform of the digital audio signal other than the distortion existing portion is generated. The specific level is a range of a signal level corresponding to a specific code in the digital audio signal.
2 can be realized by, for example, a combination of two comparators (comparators).

The delay means 103 and 104 are provided with a digital audio signal input to the distortion reduction apparatus 101 and a switching reference signal from the distortion existence discriminating means 102, which are digitally processed by a waveform smoothing means 105 to be described later. This is for preventing a time lag from the audio signal. These delay means 103 and 104 are necessary only when the device is realized by hardware, and are not necessary when the device is realized by software. The delay means 10
3 may be arranged at a stage prior to the distortion existing portion discriminating means 102.

The waveform smoothing means 105 smoothes the input digital audio signal and outputs it. In this smoothing process, for example, a filter is applied to the input digital audio signal to such an extent that the distortion of the distortion existing portion can be corrected. Since the length of the distortion existing portion is not constant, an adaptive filter or the like whose cutoff frequency changes adaptively according to the input digital audio signal is desirable.

The waveform synthesizing means 106 generates cross-fade coefficients A and B based on the switching reference signal from the distortion existence part discriminating means 102, and adds the cross-fade coefficients to the digital audio signal smoothed by the waveform smoothing means 105. A
, And the digital audio signal input to the distortion reduction apparatus 101 and output from the delay unit 104 is multiplied by a cross-fade coefficient B, and the multiplied digital audio signals are added. That is, the waveform of the smoothed digital audio signal of the distortion existing portion is cross-fade inserted into the distortion existing portion of the waveform of the original digital audio signal, and the digital audio signal with reduced distortion is synthesized.

The distortion reducing apparatus 101 having the above-described respective structures
Will be described. Here, the distortion reduction device 1
It is assumed that a digital audio signal input to 01 has a zero cross distortion having a distortion near a zero cross (a range of a specific level). FIG. 2 is a schematic diagram illustrating waveforms for explaining a distortion reduction process in the distortion reduction device according to the present embodiment. (A) shows a waveform before zero cross distortion reduction,
(B) shows a smoothed waveform, (c) shows a switching reference signal and a crossfade coefficient, and (d) shows a waveform after zero cross distortion reduction.

In FIG. 1, a digital audio signal having a zero cross distortion as shown in FIG. 2A is input to a distortion existence part discriminating means 102, a delaying means 104, and a waveform smoothing means 105 of a distortion reducing apparatus 101. You.

As shown in FIG. 2B, the waveform smoothing means 105 applies a filter to the input digital audio signal to such an extent that the distortion at the zero-cross portion can be reduced. The digital audio signal that has passed through the filter is input to the waveform synthesizing unit 106.

On the other hand, the distortion existence section discriminating means 102 outputs ± αLSB (± 1 to several L) of the input digital audio signal.
A portion where data exists in the range of SB) is detected. In the present embodiment, a portion where data exists near the zero cross is detected as a distortion existing portion where distortion exists. FIG.
As shown in FIG. 2A, a distortion existing portion near the zero cross is detected, and a switching reference signal indicating the distortion existing portion shown in FIG.

The switching reference signal from the distortion existence section discriminating means 102 is delayed by the delay means 103 so as to be temporally compatible with the time when the waveform smoothing means 105 performs the smoothing process, and the waveform synthesizing means 106 Is output to Also,
Similarly, the digital audio signal input to the distortion reduction device 101 is time-delayed by the delay unit 104 and output to the waveform synthesizing unit 106.

Then, the waveform synthesizing means 106 cross-fades the smoothed digital audio signal from the waveform smoothing means 105 into the zero cross distortion existing portion of the digital audio signal from the delay means 104. In other words, when the waveform of a digital audio signal having zero cross distortion is smoothed using an adaptive filter or the like to reduce the zero cross distortion, even the high frequency components of the music signal are lost and the frequency characteristics are degraded. Only the zero-cross part of the digital audio signal waveform is replaced and inserted into the original digital audio signal. At this time, discontinuity occurs at the connection point of the waveform, which may cause new noise. Therefore, cross-fade addition is performed outside the distortion existing portion to smoothly connect the waveforms.

More specifically, based on the switching reference signal shown in FIG. 2C, in the area A shown in FIG. 2D, the digital audio signal from the delay means 104 is added to the cross signal shown in FIG. Multiplying by the fade coefficient A, B shown in FIG.
In the region, the digital audio signal from the waveform smoothing means 105 is multiplied by a cross-fade coefficient B shown in FIG. 2C, and the digital audio signals are added so as to cross-fade at portions other than the zero cross. That is, by synthesizing the waveforms so that the zero-cross portion becomes the digital audio signal from the waveform smoothing means 105,
As shown in FIG. 2D, the digital audio signal has reduced zero cross distortion.

As described above, the distortion reducing apparatus according to the present embodiment inputs a digital audio signal in which distortion has occurred, detects a portion where data exists in a specific level range of the digital audio signal as a distortion existing portion. , A switching reference signal is generated according to the distortion existing portion. On the other hand, the input digital audio signal is divided into two systems, one is left as it is, and the other is smoothed. Then, by multiplying the distorted digital audio signal and the smoothed digital audio signal by a cross-fade coefficient created based on the switching reference signal, the distortion existing unit uses the smoothed digital audio signal, In portions other than the distortion existing portion, both waveforms are added and synthesized using a digital audio signal having distortion. This allows
It is possible to reduce distortion of a digital audio signal in which distortion has occurred in a specific level range.

In the above-described embodiment, the switching reference signal is generated from the distorted digital audio signal input to the distortion reducing device. However, a dedicated digital audio signal for detecting the distortion is separately provided. You may make it input.

In such a case, the distortion existence portion determining means 10
2 generates a switching reference signal by detecting a distortion existing portion from a digital audio signal for detecting distortion. The delay means of the delay means 103 also takes into account the amount of delay by an external circuit. Further, the delay unit 104 and the waveform smoothing unit 1
At 05, a digital audio signal having distortion in a specific level range is input. The delay unit 104 has a delay time equivalent to that of the waveform smoothing unit 105, delays the input digital audio signal, and outputs the digital audio signal to the waveform synthesizing unit 106. The waveform smoothing means 105 smoothes the input digital audio signal and outputs the digital audio signal to the waveform synthesizing means 106. Then, the waveform synthesizing unit 106 includes the delay unit 1
Based on the switching reference signal from the distortion existing part determining means 102 input via the input section 03, cross-fade counts A and B are generated, and the digital audio signals from the delay means 104 and the waveform smoothing means 105 are cross-fade added. .

Next, the non-linear error correction device corrects the non-linear error of the digital audio signal having the distortion based on the non-linear error of the A / D converter used at the time of recording. A case in which the generated digital audio signal is reduced in zero cross distortion by the distortion reduction device of the present embodiment will be specifically described.
FIG. 3 is a schematic diagram showing a schematic configuration in a case where the distortion reduction device of the present embodiment and the nonlinear error distortion correction device are combined. 3, the non-linear error correction device 301 includes a switching unit 302, a level distribution measuring unit 303, an error distribution calculating unit 304, an error data integrating unit 305, and a table converting unit 306. Distortion reduction device 10
1 has the same configuration as that of FIG. However, the digital audio signal input to the distortion existence part discriminating means 102 is a 13-bit digital audio signal before the nonlinear error correction, and the delay means 104 and the waveform smoothing means 105
Is a 16-bit digital audio signal having a zero-cross distortion with the non-linear error output from the non-linear error correction device 301 corrected.

First, the non-linear error correction device 301 will be described. In FIG. 3, the nonlinear error correction device 301
Is to correct a non-linear error based on the frequency of appearance of a digital code using the statistical characteristics of a digital audio signal. That is, the level distribution (distribution indicating the frequency of appearance of each code) of a digital audio signal recorded using an ideal A / D converter has a characteristic like a normal distribution centered on a zero level, but is non-linear. In an A / D converter having an error, the level width is not constant due to a bit error, and the data to be converted is shifted between adjacent levels. , And a code having an extremely high appearance frequency or an extremely low occurrence code is generated depending on the code.

Therefore, the level distribution of the digital audio signal is smoothed to reduce the unevenness of the appearance frequency, and approximated to the ideal level distribution when the A / D converter has no nonlinear error. Is divided by the level distribution after smoothing to calculate the distribution of nonlinear errors at each level of the A / D converter. By integrating the distribution of the non-linear error to obtain a conversion table capable of correcting the non-linear error, and converting the input digital audio signal into a table, the non-linear error can be corrected.

Specifically, assuming that the appearance frequency of the level i of the digital audio signal is g (i) and the smoothed level distribution is h (i), the nonlinear error distribution N (i) is N (i) = g (i) / h (i) (1)

Then, the conversion table T (i) is obtained from the N (i) by integrating as shown in the following equation. T (0) = 0 (2) T (i) = T (i-1) + N (i) (i> 0) (3) T (i) = T (i + 1) -N (i) (i <0 ) (4)

Or T (0) = 0 (5) T (i) = T (i-1) + [{N (i) + N (i-1)} / 2] (i> 0) (6) T (i) = T (i + 1) − [{N (i) + N (i + 1)} / 2] (i <0) (7)

At this time, the bit length of the conversion table T (i) is made longer than the bit length of the input digital audio signal to extend the bit length, so that the nonlinear error can be corrected with high accuracy. For example, it is possible to convert a signal level with 13-bit accuracy into a signal level with 16-bit accuracy.

That is, when a 13-bit digital audio signal having a non-linear error due to the A / D converter used for recording is input to the non-linear error correction device 301, the switching device 302 first inputs the digital audio signal to the level distribution measuring device 303. , The level distribution representing the appearance frequency of each code of the digital audio signal is measured. Next, the error distribution calculating means 304 obtains an error distribution by dividing the original level distribution by using the smoothed result in order to reduce unevenness of the appearance frequency of the level distribution code. Next, the error data integrating means 305 sequentially integrates the error data to obtain a conversion table.

Thereafter, the switching means 302 is switched, and the data of the digital audio signal having a non-linear error is converted by the table conversion means 306 based on the conversion table and output. Here, the output digital audio signal is output as a 16-bit digital audio signal whose bit length is extended by the conversion table.

The digital audio signal output from the non-linear error correction device 301 is output as a digital audio signal in which a zero-cross portion has distortion. The cause of the zero-cross distortion and a conventional method for reducing the zero-cross distortion will be described. FIG. 4 is a schematic diagram showing an example of a digital audio signal waveform for explaining zero cross distortion. (A) A / D with high A / D conversion accuracy
(B) shows a case where an A / D converter having a non-linear error is used, (c) shows a case where the non-linear error of (b) is corrected, and (d) shows a case where the non-linear error is corrected. (C) shows a case where a sliding band filter is used,
(E) shows a case where the ε-separated nonlinear filter is used in (c), and (f) shows a case where linear interpolation processing is used in (c).

FIG. 4A shows the waveform of a digital audio signal when an A / D converter having good linearity of A / D conversion characteristics is used, and the digital audio signal when there is no nonlinear error or zero cross distortion. The signal is shown. In contrast, when an A / D converter having a non-linear error is used,
As shown in FIG. 4B, the data of the zero cross portion may be compressed and lost due to the accumulated bit error. In the successive approximation type A / D converter in the early stage of PCM recording, the precision of each bit of the internal D / A converter was poor, and each bit had its own error. In particular, -1 (FFF
Since all bits are inverted between F) and 0 (0000), a level error is generated in which the unique error of all bits is added. Therefore, a large distortion occurs at the zero cross point, and the width of one LSB at the zero cross point becomes larger than the width of the other one LSB.

When the non-linear error of the digital audio signal shown in FIG. 4B is corrected, the signal level of each section is reproduced to be close to the original waveform, and the waveform becomes as shown in FIG. 4C. However, the minute level signal near the zero cross
Originally, it is lost at the time of A / D conversion, so it is impossible to completely restore the data. When the above-described nonlinear error is corrected for such a lost signal, the 1LSB level is enlarged, a large step waveform is generated, and the quantization distortion is increased as shown in FIG.

In order to reduce the zero-cross distortion of the digital audio signal shown in FIG. 4C, a process using a sliding filter and an ε-separation nonlinear filter is performed, and a portion where the zero-cross level disappears is subjected to a linear interpolation process. When applied, the waveforms are as shown in FIGS. 4 (d), 4 (e) and 4 (f). Although each has some effect, if each process is performed to such an extent that the zero cross distortion can be sufficiently reduced, even harmonic components of the music signal are lost.

Therefore, the distortion reducing device of the present embodiment
Effectively reduce zero cross distortion. FIG. 5 is a schematic diagram illustrating a waveform after performing each processing in the distortion reduction device of the present embodiment. (A) shows the waveform of the input digital audio signal, (b) shows the waveform of the digital audio signal after smoothing, and (c) shows the waveform obtained by cutting out the portion other than the zero-cross portion by the cross-fade coefficient B. Show,
(D) shows a waveform obtained by cutting out the zero cross portion by the crossfade coefficient A, and (e) shows a waveform of the digital audio signal after the crossfade is inserted.

The non-linear error correction device 30 shown in FIG.
The digital audio signal in which zero cross distortion has occurred due to the nonlinear error correction of 1 is input to the distortion reduction device 101,
These are input to the delay unit 104 and the waveform smoothing unit 105, respectively. The 13-bit digital audio signal before the correction of the non-linear error is provided by the distortion existence section discriminating means 102.
To enter.

FIG. 5 (c)
As shown in the figure, ± 1 of the input digital audio signal
A zero-crossing part where data exists in the LSB range is detected as a distortion existing part, and based on the detected distortion existing part, a switching reference signal as shown in FIG. And outputs it to the waveform synthesizing means 106.

Further, the waveform smoothing means 105
As shown in (b), a digital audio signal in which the zero-cross distortion of the 16-bit digital audio signal in which the non-linear error has been corrected is removed by an adaptive filter is generated,
Output to the waveform synthesizing means 106. The original 16-bit digital audio signal and the filtered and smoothed 16-bit digital audio signal are input to the waveform synthesizing unit 106.

The waveform synthesizing means 106 multiplies each digital audio signal by a cross-fade coefficient based on the switching reference signal from the distortion existence part judging means 102 and synthesizes them, as shown in FIG. Output as a digital audio signal with reduced zero cross distortion.

As described above, a portion where data exists within a range of ± 1 LSB from the original 13-bit digital audio signal is determined as a zero-cross portion where zero-cross distortion has occurred, and a switching reference signal is generated. Smoothing digital audio signal with expanded zero cross distortion by correction,
Based on the switching reference signal, the waveform of the digital audio signal whose zero-cross distortion has been smoothed is cross-fade-inserted into the zero-cross part of the digital audio signal waveform after the non-linear error correction, and synthesized. A digital audio signal in which the distortion of the zero crossing portion caused by the above is reduced can be obtained.

Here, in the above-described distortion existence portion discriminating means, the discrimination of the zero cross portion is discriminated based on ± 1 LSB of the 13-bit digital audio signal.
In the value of the digital audio signal converted into 6 bits, the determination may be made in a range corresponding to ± 1 LSB at 13 bits.

[0052]

According to the present invention, it is possible to reduce the distortion of a digital audio signal generated in a specific level range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of one embodiment of a distortion reduction device of the present invention.

FIG. 2 is a schematic diagram showing waveforms for explaining a distortion reduction process in the distortion reduction device of the present embodiment. (A) shows a waveform before the zero cross distortion is reduced, (b) shows a smoothed waveform, (c) shows a switching reference signal and a cross fade coefficient, and (d) shows a waveform after the zero cross distortion is reduced. Is shown.

FIG. 3 is a schematic diagram showing a schematic configuration in a case where a distortion reduction device and a nonlinear error correction device of the present embodiment are combined.

FIG. 4 is a schematic diagram showing an example of a digital audio signal waveform for explaining zero cross distortion. (A) is A /
The case where an A / D converter with high D conversion accuracy is used is shown,
(B) shows a case where an A / D converter having a nonlinear error is used, (c) shows a case where the nonlinear error of (b) is corrected, and (d) shows a case where a sliding band filter is used for (c). (E) shows the case where the ε-separated nonlinear filter is used in (c), and (f) shows the case where the linear interpolation processing is used in (c).

FIG. 5 is a schematic diagram showing a waveform after performing each processing in the distortion reduction device of the present embodiment. (A) shows the waveform of the input digital audio signal, (b) shows the waveform of the digital audio signal after smoothing, and (c) shows the waveform obtained by cutting out the portion other than the zero-cross portion by the cross-fade coefficient B. (D) shows a waveform obtained by cutting out the zero-cross portion by the crossfade coefficient A, and (e) shows a waveform of the digital audio signal after the crossfade is inserted.

[Explanation of symbols]

101... Distortion reducing device, 102... Distortion existence part discriminating means, 103... Delaying means, 104.
..Waveform smoothing means, 106.
A non-linear error correction device, 302, switching means, 303
Level distribution measuring means, 304 error distribution calculating means
305 error data integrating means, 306 table conversion means

Claims (4)

[Claims] 1. A distortion reduction apparatus for reducing distortion of a digital audio signal, comprising: a distortion existence section discriminating means for detecting a range of a specific level in which the digital audio signal distortion exists as a distortion existence section and generating a switching reference signal; A waveform smoothing means for smoothing the distortion of the digital audio signal, and using a waveform of the digital audio signal from the waveform smoothing means in a period corresponding to the distortion existing portion based on the switching reference signal, A waveform synthesizing unit for outputting a digital audio signal in which waveforms are continuously connected by cross-fading using a waveform of the original digital audio signal in a period other than a distortion existing portion. . 2. A distortion reduction method for reducing distortion of a digital audio signal, wherein a range of a specific level in which the distortion of the digital audio signal exists is detected as a distortion existing portion, a switching reference signal is generated, and a switching reference signal is generated. Distortion is smoothed, and a waveform of the smoothed digital audio signal is used in a period corresponding to the distortion existing portion based on the switching reference signal, and in a period other than the distortion existing portion, the waveform of the original digital audio signal is used. A distortion reduction method, comprising outputting a digital audio signal in which waveforms are continuously connected by crossfading using the waveforms. 3. A distortion reducing apparatus for reducing zero cross distortion caused by correcting a non-linear error of a digital audio signal having a non-linear error, wherein data exists in a range of ± 1 LSB of the digital audio signal before the non-linear error correction. A zero-cross part determining means for detecting a part to be changed as a zero-cross part to generate a switching reference signal; a waveform smoothing means for smoothing the digital audio signal after the non-linear error correction; The waveform of the digital audio signal from the waveform smoothing means is used in a period corresponding to the zero cross portion based on the switching reference signal, and the digital audio signal after the nonlinear error correction is used in a period other than the zero cross portion. Outputs a digital audio signal in which waveforms are continuously connected by crossfading using waveforms Distortion reduction apparatus characterized by comprising a shape combining means. 4. A distortion reduction method for reducing zero cross distortion caused by correcting a non-linear error of a digital audio signal having a non-linear error, wherein data exists in a range of ± 1 LSB of the digital audio signal before the non-linear error correction. The switching reference signal is generated by detecting a portion to be changed as a zero cross portion, the digital audio signal after the nonlinear error correction is smoothed, and the smoothing is performed during a period corresponding to the zero cross portion based on the switching reference signal. Using the waveform of the digital audio signal thus obtained, and outputting a digital audio signal whose waveform is continuously connected by crossfading using the waveform of the digital audio signal after the non-linear error correction in a period other than the zero crossing portion. Characteristic distortion reduction method.