Signal modification circuit

Abstract

A signal modification circuit receives an input signal and produces an output having a modified characteristic. When the signal modification circuit is embodied in an audio circuit receiving an analog audio signal having a first variant level at its input, the audio circuit produces an output signal having a second variant level in which a frequency characteristic in a high frequency range is modified so that the second variant level decreases in accordance with a function of l/fm (f being frequency and m being an integer determined depending upon the nature of the audio signal) relative to the first variant level while being trapped in selected discrete frequencies. For this purpose a combination of a low-pass filter and a plurality of trap filters connected in series with one another, or a combination of a low-pass filter and a plurality of band-pass filters connected in parallel to one another. Instead, a convolution operating circuit is used which performs a convolution operation between an input digital signal and a unitary impulse response signal. In accordance with such audio circuit, the local position of musical sounds is stabilized and the articulation of spoken words is improved. The signal modification circuit according to the invention is also applicable to digital-to-analog converting circuit.