Patent ID: RE38822

Claim:
A circuit comprising: selecting means for selecting a frequency band of an audio input signal; harmonics generator means for generating harmonics of signals in the selected frequency band of the audio input signal to provide generated harmonics; adding means for supplying a sum of the audio input signal and scaled harmonics; level detecting means for detecting a level of at least a part of the spectrum of the audio input signal including the selected frequency band; and scaling means for scaling the generated harmonics in response to the detected level to provide the scaled harmonics, and wherein the harmonics generator comprises: a zero-crossing detector for detecting zero crossings in signals including signals of the selected frequency band; and a waveform generator for generating a waveform in response to detected zero crossings, an amplitude of the generated waveform being controlled by the level supplied by the level detecting means, and wherein the waveform generator comprises: a current source controlled by the detected level supplied by the level detecting means; a capacitance; and means for charging and discharging the capacitance in response to the detected zero crossings.