Speech signal pitch detection uses the residual signal output of an LPC (linear prediction coder) filter. The residual signal (or its Hilbert transform) is divided into frames of 20 milliseconds, and each frame searched for signal peak periodicity by first detecting the highest peak, then detecting a...http://www.google.fr/patents/US4561102?utm_source=gb-gplus-shareBrevet US4561102 - Pitch detector for speech analysis
