Method and apparatus for processing digital audio signal

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

detecting extreme values in an audio waveform represented by the digital audio signal, the detected extreme values including a detected maximum value and a detected minimum value;

counting samples between a sample corresponding to first one of the detected extreme values and a sample corresponding to second one of the detected extreme values to get a count result;

detecting an audio frequency represented by the digital audio signal in response to the count result;

calculating a difference between each of the detected extreme values and a value of a sample which immediately precedes a sample corresponding to the present detected extreme value;

selecting one from predetermined frequency bands different from each other;

selecting one from predetermined coefficients different from each other;

multiplying the calculated differences by the selected coefficient to get corrective values respectively;

deciding whether or not the detected audio frequency represented by the digital audio signal is in the selected frequency band; and

when it is decided that the detected audio frequency is in the selected frequency band, adding, to the detected maximum value, corresponding one of the corrective values, and subtracting, from the detected minimum value, corresponding one of the corrective values.

2. A method as recited in claim 1 , wherein the predetermined coefficients are smaller than 1.0.

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

means for detecting extreme values in an audio waveform represented by the digital audio signal, the detected extreme values including a detected maximum value and a detected minimum value;

means for counting samples between a sample corresponding to first one of the detected extreme values and a sample corresponding to second one of the detected extreme values to get a count result;

means for detecting an audio frequency represented by the digital audio signal in response to the count result;

means for calculating a difference between each of the detected extreme values and a value of a sample which immediately precedes a sample corresponding to the present detected extreme value;

means for selecting one from predetermined frequency bands different from each other;

means for selecting one from predetermined coefficients different from each other;

means for multiplying the calculated differences by the selected coefficient to get corrective values respectively;

means for deciding whether or not the detected audio frequency represented by the digital audio signal is in the selected frequency band; and

means for, when it is decided that the detected audio frequency is in the selected frequency band, adding, to the detected maximum value, corresponding one of the corrective values, and subtracting, from the detected minimum value, corresponding one of the corrective values.

4. An apparatus as recited in claim 3 , wherein the predetermined coefficients are smaller than 1.0.

5. A computer readable memory storing a computer program for enabling a computer to execute steps of processing a digital audio signal having a sequence of samples, the steps comprising:

detecting extreme values in an audio waveform represented by the digital audio signal, the detected extreme values including a detected maximum value and a detected minimum value;

counting samples between a sample corresponding to first one of the detected extreme values and a sample corresponding to second one of the detected extreme values to get a count result;

detecting an audio frequency represented by the digital audio signal in response to the count result;

calculating a difference between each of the detected extreme values and a value of a sample which immediately precedes a sample corresponding to the present detected extreme value;

selecting one from predetermined frequency bands different from each other;

selecting one from predetermined coefficients different from each other;

multiplying the calculated differences by the selected coefficient to get corrective values respectively;

deciding whether or not the detected audio frequency represented by the digital audio signal is in the selected frequency band; and

when it is decided that the detected audio frequency is in the selected frequency band, adding, to the detected maximum value, corresponding one of the corrective values, and subtracting, from the detected minimum value, corresponding one of the corrective values.

6. An apparatus for processing a digital audio signal, comprising:

first means for detecting an extreme in an audio waveform represented by the digital audio signal;

second means for detecting a local audio frequency represented by the digital audio signal;

third means for deciding whether or not the local audio frequency detected by the second means is in a limited frequency band;

fourth means for, when the third means decides that the local audio frequency is in the limited frequency band, emphasizing the extreme detected by the first means;

fifth means for, when the third means decides that the local audio frequency is not in the limited frequency band, keeps unchanged the extreme detected by the first means; and

sixth means for keeping unchanged the audio waveform except for the extreme.

7. An apparatus as recited in claim 6 , further comprising seventh means for changing the limited frequency band.

8. An apparatus as recited in claim 6 , further comprising seventh means for changing a degree of the emphasis by the fourth means.