Voice messaging system with pitch tracking based on adaptively filtered LPC residual signal

摘要

A voice messaging system, wherein linear predictive coding (LPC) parameters, pitch, and preferably other excitation information is derived from a human voice input, encoded, and transmitted and/or stored, to be called up later to provide a speech output which is nearly identical to the original speech input. The invention features adaptive filtering of the residual signal. The residual signal derived from LPC estimation is adaptively filtered, and then is used as the input to a conventional pitch estimation procedure. The adaptive filtering step uses the first reflection coefficient (k.sub.1) to realize a simple filter (e. g., A(z) =(1-k.sub.1 z.sup.-1).sup.-1. This filter removes high frequency noise from the residual signal during voiced periods, but does not remove the high frequency energy which contains important information during the unvoiced periods of speech. Preferably the above preprocessing technique is also combined with a postprocessing technique, wherein dynamic programming is used to optimally track pitch and voicing information through successive frames.