JPH11312367A - How to remove signal distortion - Google Patents

Abstract

(57) [Problem] To provide a distortion removal method for correcting distortion of a reproduction signal. A distortion removing method for removing distortion from a reproduced signal of a digital recording medium, the distortion of the reproduced signal being analyzed for each frequency (120 steps), and as a result, data forming a portion determined to be distorted. It is characterized in that subtraction or addition is performed for each byte one bit at a time (130 steps).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital signal copying technique, and more particularly to a method for removing distortion generated when an audio signal is copied.

[0002]

SUMMARY OF THE INVENTION Music CDs (Compact
Disk) is most suitable as a source sound source besides enjoying playing because there is no deterioration of sound. In addition, MD (Mini Dis
k) has been remarkably popular in recent years, and has no sound deterioration like CDs and has a smaller shape than CDs.
Is often copied to an MD and used for going out.

[0003] Such a digital recording medium can be used semi-permanently if there is a reproducing device without deterioration of sound in the medium itself. However, if the reproduction signal of the CD has distortion, M
The copy data in D may be different from the original data.

For example, if a distortion is generated near the peak of the original reproduced signal for some reason and another peak is generated, when this is recorded on the MD, the MD recording method is performed because of the compression recording method. During MD playback, there is a possibility that a playback signal completely different from the original data will result. Such a phenomenon will be described with reference to FIG. In each waveform of FIG.
The solid line indicates the case where the volume of the reproduced data is increased due to the distortion, and the broken line indicates the case where the volume of the reproduced data is decreased due to the distortion.

[0005] If the CD output data is distorted by α from the original waveform as shown in (A), if this is compressed and recorded, MD recording data as shown in (B) is recorded. Here, the distorted portion of the waveform is also compressed to α ′. When this MD recording data is reproduced, it becomes MD reproduction output data shown in (C). At this time, the distorted portion α ″ is reproduced with being emphasized more than the distorted portion α of the CD output data of (A). Through such a process, the weak distortion that is inconspicuous in the CD output data is greatly enlarged. The resulting MD playback signal is completely different from the CD output data.

The present invention provides a distortion removing method for correcting such distortion of a reproduced signal.

[0007]

According to the present invention, in order to remove the above-mentioned distortion of the reproduced signal which has an influence on the reproduced signal reproduced from the digital recording medium, the distortion is analyzed for each frequency. As a result, the subtraction or the addition is performed on the data bytes constituting the portion determined to be distorted. Such distortion removal is performed for each frequency for all frequencies of the reproduction signal, and subtraction or addition is performed for each bit.

The determination of the distortion portion is made based on the output change rate and the time from the immediately preceding output peak. Specifically, when the output change rate changes from 0 to the sampling clock from the immediately preceding output peak to 0 or more, the operation is determined to be distortion and the operation is shifted to the operation of eliminating the distortion. The signal is subtracted out until the rate becomes negative. Conversely, if the output change rate is extremely negatively larger than the immediately preceding byte change rate, the operation is determined to be distortion and the operation shifts to the operation of eliminating the distortion, and the byte change rate determined to be distortion is extremely negative. The signal is added and removed until it can be determined that the signal does not increase in the direction.

[0009] The distortion is removed after a byte determined to be distortion is found until a reproduced signal whose output change rate is greater than 0 is found. The amount of bits removed during this time is the same as the amount of bits removed in the bytes forming the portion determined to be distorted. Here, if the number of times of subtraction or addition of the byte determined to be distorted is counted and the removed bit amount is stored, and the bit amount corresponding to the counted number is subtracted or added, the distortion can be removed more quickly. be able to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings, in which distortion is subtracted and deleted. In the following description, as shown in FIG. 2, the minimum volume (output) of the quantized waveform is defined as 1 byte and the data captured with 1 clock is defined as 1 byte.

The circuit shown in FIG. 3 is a circuit that removes distortion from audio data that has been distorted as shown in FIG. This circuit is
An input buffer 10 for separating audio data into three types of signals: a clock signal, an L / R timer signal, and source data;
Determine the peak value and average value of the volume of the source data and
A peak / average value detection circuit 12 input to U15, a change rate detection circuit 13 for obtaining a change rate of the volume of the source data and inputting it to the CPU 15, a clock timer circuit 14 for inputting a clock signal to the CPU 15, A delay circuit 11 for delaying the input to the subtractor 16;
, A subtractor 16 for removing the distortion from the source data, an output buffer 18 for outputting the source data from which the distortion has been removed, and C in one byte.
Memory 1 for storing how many times the PU 15 has issued the subtraction instruction
7 is comprised.

The detailed operation and data flow of each circuit are as follows. First, the input audio data is separated by the input buffer 10 into three digital signals of a clock signal, an L / R timer signal, and source data. The clock signal and the L / R timer signal are input to the CPU 15 via the clock timer circuit 14, and the source data is input to the peak value / average value detection circuit 12 and the change rate detection circuit 13.
The source data input to the peak value / average value detection circuit 12 is subjected to D / A conversion to become analog source data.
From the analog source data, the peak value of the sound volume and the average value of the sound volume within an arbitrary time are obtained, and the obtained peak value and average value are sent to the CPU 15. The source data input to the change rate detection circuit 12 is also D / A converted to analog source data, and the change rate of the volume within an arbitrary time is obtained from the analog source data and sent to the CPU 15.

The CPU 15 includes a peak / average value detection circuit 1
If the change rate after 2 to 5 sampling clocks from the peak sent from 2 is 0 or more, this byte is regarded as being distorted and a subtraction instruction is output to the subtractor 16.
Also, the count 1 is added to the memory 17 by this subtraction instruction. The subtractor 16 that has received the subtraction instruction determines that the signal is distorted from the source data delayed by the delay circuit 11 by the same time as the peak / average value detection circuit 12 (or the change rate detection circuit 13) + the delay time of the CPU 15. One bit is subtracted from the set byte.

The byte obtained by subtracting one bit from the distortion portion is input to the change rate detection circuit 19, and the change rate is measured. The measured change rate is input to the CPU 15, and if the change rate is 0 or more, it is determined that the distortion is still occurring, and the subtraction command is output to the subtractor 16 again. If the rate of change is less than 0, it is determined that the distortion has disappeared, and the byte with the distortion is output to the outside via the output buffer 18.

The flowchart shown in FIG. 4 shows a method for removing distortion of a CD reproduction signal using the circuit of FIG.

The CD reproduction data input to the input buffer 10 in 100 steps is separated into three digital signals of a clock signal, an L / R timer signal, and source data by the input buffer 10. Of the separated data, the source data is input to the peak / average value detection circuit 12 and the change rate detection circuit 13, and the peak value, average value, and change rate are measured in each circuit, and the measurement result is sent to the CPU 15. Is entered. Next, at step 110, the CPU 15 sets the counter value of the memory 17 to 0 and proceeds to step 120 to determine whether the byte is a distorted byte. The distortion is determined based on the peak value and the change rate measured by the peak / average value detection circuit 12 and the change rate detection circuit 13.
When the change rate becomes 0 or more after 5 sampling clocks, it is determined that the byte is distorted.

If it is determined at step 120 that there is distortion, the CPU
15 proceeds to step 130 to transmit a subtraction command to the subtractor 16. Upon receiving the subtraction command, the subtracter 16 subtracts one bit from the byte determined to be distorted. The subtraction command is also transmitted to the memory 17 in addition to the subtractor 16, and upon receiving the subtraction command, the memory 17 adds 1 to the counter value at step 140. When 1 is added to the counter value of the memory 17, the process returns to step 120, and it is determined again whether or not the byte determined to be distorted is distorted. Steps 120 to 140 are performed until the byte that is initially determined to be distorted is no longer determined to be distorted. During this time, the byte that is determined to be distorted is decremented by one bit, and the counter value is incremented by one. To go.

If it is determined in step 120 that the image is not distorted / if it is no longer determined that the image is distorted, the process proceeds to step 150 and the CPU 1
5 reads the counter value stored in the memory 17.
If the read counter value is 0, the process proceeds to step 190,
Judge whether there is the next byte, and if there is, 11
Returning to step 0, the counter value is returned to 0, and the steps from step 120 are executed again. If there is no next byte, it is determined that the distortion removal processing has been completed for all the data, and the distortion removal ends.

If the counter value is not 0 at step 150, the process proceeds to step 160. At step 160, the next byte is fetched, the rate of change of this byte is measured, and the measurement result is sent to CPU1.
Enter 5 At step 170, the CPU 15 determines whether the measurement result is 0 or less. 180 if less than 0
Proceeding to the stage, the byte is subtracted one bit at a time the same number of times as the counter value. If the rate of change is greater than 0, it is determined that distortion removal has been completed, and the process proceeds to step 190.

When step 180 is completed, the process returns to step 160,
Steps 160 to 180 are repeatedly executed. 160-18
By the 0 stage, the reproduction waveform of the CD becomes the waveform shown in FIG. 5, and becomes a waveform close to the original CD output data.

According to the same circuit configuration and the same flowchart, distortion can be added to correct the waveform. At this time, the subtraction instruction becomes an addition instruction, and the subtractor 16 operates as an adder. The criterion for judging distortion is that when the change rate becomes extremely negative in the negative direction than the change rate of the immediately preceding byte after 2 to 5 sampling clocks from the immediately preceding output peak, it is judged as distortion. The criterion for determining that distortion has disappeared is that distortion has been eliminated when distortion has been deleted so that the change rate of the byte determined to be distortion has not become extremely large in the negative direction. Other operations are the same as in the case where the distortion is deleted by subtraction.

[0022]

According to the distortion removal method of the present invention, even when a reproduced signal of a digitally recorded signal has a peak near the original peak due to distortion, the peak portion can be deleted. , It can be reproduced without largely changing from the original reproduction signal.

[Brief description of the drawings]

FIG. 1 is an exemplary view showing a process in which a distortion portion is emphasized by compression recording.

FIG. 2 is a diagram showing definitions of bits and bytes.

FIG. 3 is a circuit diagram of a distortion removal circuit.

FIG. 4 is a flowchart of distortion removal.

FIG. 5 is a waveform after distortion removal.

[Explanation of symbols]

 Reference Signs List 10 input buffer 11 delay circuit 12 peak / average value detection circuit 13, 19 change rate detection circuit 14 clock timer circuit 15 CPU 16 subtractor 17 memory 18 output buffer

Claims (9)

[Claims] 1. A distortion removing method for removing distortion from a reproduction signal of a digital recording medium, wherein the distortion is analyzed for each frequency of the reproduction signal, and as a result, a data byte forming a portion determined to be distorted is removed. And performing a subtraction or an addition. 2. For all frequencies of the reproduced signal, 1
2. The distortion removing method according to claim 1, wherein the distortion is removed for each waveform. 3. The distortion removal method according to claim 1, wherein the subtraction or the addition is performed one bit at a time. 4. The distortion removing method according to claim 1, wherein the analysis of the distortion is performed based on a rate of change of the output and a time from an immediately preceding output peak. 5. The distortion analysis is performed by calculating two points from the immediately preceding output peak.
5. The distortion removing method according to claim 4, wherein the distortion is determined when the rate of change of the output changes from 0 to 5 or more during the sampling clock. 6. The method according to claim 1, wherein the subtraction of the data byte is performed until the rate of change of the byte determined as distortion is less than zero.
The method for removing distortion according to any one of the above. 7. The distortion removing method according to claim 1, wherein the subtraction or the addition is performed until a byte whose output change rate is greater than 0 is found after finding a byte determined to be distortion. 8. The distortion removal method according to claim 7, wherein the subtraction or addition performed until a byte whose output change rate is greater than 0 is found is performed by the same amount as the number of bits subtracted or added from the bytes constituting the portion determined to be distorted. . 9. The distortion removing method according to claim 8, wherein the number of times of subtraction or addition of the byte determined to be distorted is counted and the amount of removed bits is stored, and the bit is subtracted or added one bit at a time equal to the counted number. .