Method and apparatus for processing digital audio signal and related computer program

1. A method of processing a digital audio signal having a sequence of samples, the method comprising the steps of:

using an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

using an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

using an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

designating ones among samples in response to the detected inter-extreme sample number as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

2. A method as recited in claim 1 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

3. A method as recited in claim 1 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

4. An apparatus for processing a digital audio signal having a sequence of samples, the apparatus comprising:

an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

means for generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

means for designating ones among samples in response to the detected inter-extreme sample number as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

means for correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

5. An apparatus as recited in claim 4 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value of represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

6. An apparatus as recited in claim 4 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

7. A non-transitory computer readable medium storing a computer program for processing a digital audio signal having a sequence of samples, the computer program comprising the steps of:

using an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

using an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

using an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

designating ones among samples in response to the detected inter-extreme sample number as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

8. A non-transitory computer readable medium as recited in claim 7 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

9. A non-transitory computer readable medium as recited in claim 7 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

10. A method of pre-emphasizing a digital audio signal having a sequence of samples to generate a pre-emphasized digital audio signal before the pre-emphasized digital audio signal is compressed by an encoder, the pre-emphasizing being designed to compensate for audio quality degradation caused by the compression by the encoder, the method comprising the steps of:

using an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

using an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

using an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

designating ones among samples in response to the detected inter-extreme sample number and the degree of the audio quality degradation as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

11. A method as recited in claim 10 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value of represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value of represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

12. A method as recited in claim 10 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

13. An apparatus for pre-emphasizing a digital audio signal having a sequence of samples to generate a pre-emphasized digital audio signal before the pre-emphasized digital audio signal is compressed by an encoder, the pre-emphasizing being designed to compensate for audio quality degradation caused by the compression by the encoder, the apparatus comprising:

an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

means for generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

means for designating ones among samples in response to the detected inter-extreme sample number and the degree of the audio quality degradation as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

means for correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

14. An apparatus as recited in claim 13 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value of represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

15. An apparatus as recited in claim 13 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

16. A non-transitory computer readable medium storing a computer program for pre-emphasizing a digital audio signal having a sequence of samples to generate a pre-emphasized digital audio signal before the pre-emphasized digital audio signal is compressed by an encoder, the pre-emphasizing being designed to compensate for audio quality degradation caused by the compression by the encoder, the computer program comprising the steps of:

using an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

using an inter-extreme sample number detector for detecting a number of samples in time positions between time positions of two temporally-adjacent samples among samples representing respective detected extreme values to get a detected inter-extreme sample number;

using an inter-extreme difference calculator for calculating a difference between the detected extreme values represented by said two temporally-adjacent samples to get a calculated inter-extreme difference;

generating a corrective value in response to the detected inter-extreme sample number and the calculated inter-extreme difference, the generated corrective value being updated each time a new extreme value is detected;

designating ones among samples in response to the detected inter-extreme sample number and the degree of the audio quality degradation as objects to be corrected, the designated samples including at least (1) a sample adjacently following the older of said two temporally-adjacent samples, (2) a sample adjacently preceding the newer of said two temporally-adjacent samples, and (3) a sample being one of said two temporally-adjacent samples; and

correcting the designated samples in response to at least one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) a generated corrective value next to the currently-generated corrective value.

17. A non-transitory computer readable medium as recited in claim 16 , wherein the correcting is such that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from a value represented by the sample adjacently following the the older of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to a value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is added to the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a maximum value and a minimum value respectively, and that one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is added to the value represented by the sample adjacently following the older of said two temporally-adjacent samples and is added to the detected extreme value represented by the older of said two temporally-adjacent samples and one of (1) the currently-generated corrective value, (2) the previously-generated corrective value, and (3) the generated corrective value next to the currently-generated corrective value is subtracted from the value represented by the sample adjacently preceding the newer of said two temporally-adjacent samples and is subtracted from the detected extreme value represented by the newer of said two temporally-adjacent samples when the detected extreme values represented by the newer and older of said two temporally-adjacent samples are a minimum value and a maximum value respectively.

18. A non-transitory computer readable medium as recited in claim 16 , wherein the generated corrective value and the designated samples are selectable from candidate ones designed to compensate for different degrees of degradation in audio quality of the digital audio signal.

19. A method of processing a digital audio signal having a sequence of samples, the method comprising the steps of:

using an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

repetitively detecting a local period of the audio waveform;

using an inter-extreme difference calculator for repetitively calculating a difference between two detected extreme values and thereby repetitively detecting a local amplitude of the audio waveform; and

correcting a sample corresponding to the detected extreme value, a sample adjacently preceding the sample corresponding to the detected extreme value, and a sample adjacently following the sample corresponding to the detected extreme value in response to the detected local period and the detected local amplitude.

20. An apparatus for processing a digital audio signal having a sequence of samples, comprising:

an extreme detector for detecting every extreme value in an audio waveform represented by the digital audio signal, the extreme value being either a maximum value or a minimum value;

means for repetitively detecting a local period of the audio waveform;

an inter-extreme difference calculator for repetitively calculating a difference between two detected extreme values and thereby repetitively detecting a local amplitude of the audio waveform; and

means for correcting a sample corresponding to the detected extreme value, a sample adjacently preceding the sample corresponding to the detected extreme value, and a sample adjacently following the sample corresponding to the detected extreme value in response to the detected local period and the detected local amplitude.