Patent ID: 7003469

Claim:
An audio signal processing apparatus in which a waveform of a digital audio signal to be replayed is processed, the apparatus comprising: frequency bandwidth expanding means for expanding a frequency bandwidth of the digital audio signal through conversion of a sampling frequency at which the digital audio signal is sampled; low-pass filtering means for performing low-pass filtering on the digital audio signal expanded in the frequency bandwidth, the low-pass filtering involving a cut-off frequency corresponding to the converted sampling frequency; detecting means for detecting an interval of time between two adjacent waveform peaks of the low-pass-filtered digital audio signal, a polarity of a gradient of the waveform changing at each of the two adjacent waveform peaks and the interval of time being detected by measuring the number of times of sampling based on the converted sampling frequency; difference data calculating means for calculating data of a difference between current data of the low-pass-filtered digital audio signal and past data of the low-pass-filtered digital audio signal; weighting means for weighting the data of the difference depending on the interval of time between the two adjacent waveform peaks; and producing means for producing output data based on both the low-pass-filtered digital audio signal and the weighted data of the difference.