To improve reproduced sound quality by expanding a reproduction frequency band to digital audio signals the high frequency reproducing limit of which is decided by the sampling theorem.
Digital audio signals are given to an over-sampling type LPF(low-pass filter) 102 for over-sampling and frequency band limitation. Moreover, a band-pass filter 103, a rectifier circuit 104 and a high-pass filter 105 are used for generating higher harmonics higher than the frequency band of the input signals. A level control circuit 107 performs level control on the basis of the spectral intensity of the high frequency band components of the input signals detected with a spectrum analysis circuit 106, and an adder circuit 108 adds the higher harmonics to the input signal. Next, the over-sampling means 109 performs over-sampling at a still higher sampling frequency, and outputs audio signals of an expanded frequency band through an LPF 110.
EJIMA NAOKI
IWATA KAZUYA
