Apparatus and method for processing audio data

Abstract

An ExOR circuit performs volume comparison between a sound level expressed by audio data and zero level by detecting whether or not the sign of audio data at a given time stored in a first register is inverted from a sign of audio data which is one sample before the audio data at the given time stored in a second register. A shift register for shifting audio data outputted from the first register changes the sound level by changing the shift amount every time the ExOR circuit detects the sign inversion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more apparent from the following detailed description when the accompanying drawings are referenced.

FIG. 1 is a diagram showing a structure of an audio data processing apparatus embodying the invention;

FIG. 2A is a flowchart (No. 1) for explaining operations of the audio data processing apparatus;

FIG. 2B is a flowchart (No. 2) for explaining operations of the audio data processing apparatus;

FIG. 3A is a diagram showing change in a sound level by mute processing of fade-out when timings of changing shift amounts in a shift register are not considered;

FIG. 3B is a diagram for explaining timings of changing shift amounts in the shift register;

FIG. 3C is a diagram showing change in a sound level by mute processing of fade-out when timings of changing shift amounts in the shift register are considered;

FIG. 4A is a diagram for explaining a first modified example of the structure of the audio data processing apparatus of FIG. 1;

FIG. 4B is a diagram for explaining a second modified example of the structure of the audio data processing apparatus of FIG. 1;

FIG. 5A is a diagram for explaining a third modified example of the structure of the audio data processing apparatus of FIG. 1;

FIG. 5B is a diagram for explaining a fourth modified example of the structure of the audio data processing apparatus of FIG. 1;

FIG. 6 is a flowchart (No. 3) for explaining operations of the audio data processing apparatus; and

FIG. 7 is a diagram for explaining a fifth modified example of the structure of the audio data processing apparatus of FIG. 1.

Claims

1. An apparatus for processing audio data, comprising: a comparing unit for performing volume comparison between a sound level expressed by audio data and a given threshold; anda changing unit for changing the sound level expressed by the audio data when a result of the comparison by the comparing unit is changed.

2. The apparatus according to claim 1, wherein the given threshold is zero level.

3. The apparatus according to claim 2, wherein the audio data is expressed in the form of two's complement,the comparing unit includes a detecting unit for detecting a sign change point of the audio data, andthe changing unit changes the sound level expressed by the audio data at the sign change point.

4. The apparatus according to claim 3, wherein the detecting unit detects whether or not a sign of data at a given time of the audio data is inverted from a sign of data which is one sample before the data at the given time of the audio data.

5. The apparatus according to claim 4, further comprising: a first register for storing the audio data; anda second register for storing audio data which is one sample before the audio data stored in the first register, whereinthe detecting unit is an exclusive OR circuit which outputs exclusive OR between a sign bit of the audio data stored in the first register and a sign bit of the audio data stored in the second register.

6. The apparatus according to claim 1, wherein the changing unit is a shift register for shifting the audio data.

7. The apparatus according to claim 6, wherein the audio data is expressed in the form of two's complement,the comparing unit includes a detecting unit for detecting a sign change point of the audio data, andthe shift register changes a shift amount of the audio data every time the detecting unit detects the sign change point.

8. The apparatus according to claim 6, wherein the audio data is expressed in the form of 2's complement,the comparing unit includes a detecting unit for detecting a sign change point of the audio data, andthe shift register changes a shift amount of the audio data every time the detecting unit detects the sign change point a given number of times.

9. The apparatus according to claim 1, wherein the audio data is expressed in the form of two's complement, andthe comparing unit produces a result of the comparison based on whether or not all values of high bits in a given number of digits in the audio data correspond with a value of a sign bit of the audio data.

10. The apparatus according to claim 1, further comprising a threshold changing unit for changing the given threshold when the result of the comparison by the comparing unit is changed.

11. A method for processing audio data, comprising: performing volume comparison between a sound level expressed by audio data and a given threshold; andchanging the sound level expressed by the audio data when a result of the comparison is changed.

12. The method according to claim 11, wherein the given threshold is zero level.

13. The method according to claim 12, wherein the audio data is expressed in the form of two's complement,the volume comparison is performed by detecting a sign change point of the audio data, andwhen the sign change point is detected, the sound level expressed by the audio data is changed at the sign change point.

14. The method according to claim 13, wherein in detecting the sign change point, detection is made as to whether or not a sign of data at a given time of the audio data is inverted from a sign of data which is one sample before the data at the given time of the audio data.

15. The method according to claim 14, wherein the sign change point is detected by obtaining exclusive OR between a sign bit of the audio data at a given time and a sign bit of audio data which is one sample before the audio data.

16. The method according to claim 11, wherein by using a shift register for shifting the audio data, a sound level expressed by the audio data is changed.

17. The method according to claim 16, wherein the audio data is expressed in the form of two's complement,the volume comparison is performed by detecting a sign change point of the audio data, andevery time the sign change point is detected, a shift amount of the audio data by the shift register is changed.

18. The method according to claim 16, wherein the audio data is expressed in the form of two's complement,the volume comparison is performed by detecting a sign change point of the audio data, andevery time the sign change point is detected a given number of times, a shift amount of the audio data by the shift register is changed.

19. The method according to claim 11, wherein the audio data is expressed in the form of two's complement, anda result of the volume comparison is obtained based on whether or not all the values of high bits in a given number of digits in the audio data correspond with the value of a sign bit of the audio data.

20. The method according to claim 11, wherein the given threshold is changed when the result of the volume comparison is changed.