A waveform extractor for scalable speech coding

Waveform interpolation (WI) models for speech coding contain many parameters whose sampling rates may not be simply related so that most implementations tend to fix their rates right from the waveform extraction stage, thereby compromising quality by departing from perfect reconstruction. A waveform extractor is proposed which samples waveform cycles of the original prediction residual signal at their natural variable rate so that it can perfectly reconstruct the signal. The speech coder, which may operate at a uniform sampling rate, is coupled to the waveform extractor by means of an evolving waveform interpolator that may handle several interpolation methods and sampling rates for a variety of fixed and variable rate coders, including conventional WI coders.