DETECTOR FOR CODED SPEECH SIGNALS

摘要

The invention relates to a speech detector for determining whether or not a voice signal is present on a telephone line, particularly on timedivision multiplexed telephone channels. The known amplitude comparison speech detectors respond quickly to most voiced sounds and plosives but poorly to fricative consonants. Attempts have been made for the parallel use of another speech detector of the periodicity type but this is not much help because fricative consonants are inherently noise-like and lack sufficient periodicity. The speech detector disclosed herein is simple in structure and effective even with fricative consonants. The detector operates on coded speech signals composed of one sign bit and several amplitude bits representing the sign and amplitude of original analog speech signals. The detector comprises a zero crossing density detector section which senses the frequency of the change in the sign bits of the voice signals and a discriminator which delivers a detector output only when the sensed frequency exceeds a predetermined value. This detection output is supplied to an OR circuit to which is applied another detection output from a conventional amplitude comparison speech detector.