Algorithm for pitch extraction using zero-crossing interval sequence

A novel digital computer algorithm for pitch period analysis of connected speech is presented. The principal idea employed is to find the periodic-like portions of the speech, from its zero-crossing interval (ZCI) sequence, by an adaptive search. The algorithm requires only additions and comparisons, no multiplication. An implementation of the algorithm on a 1.5 μs memory-cycle computer (PDP-8) performs the analysis in real time, as accurately as manually performed pitch measurements from a plot of the speech waveform low-pass filtered to a bandwidth of 900 Hz in such a way that each pitch boundary is marked on a zero-crossing. Although 12 threshold values are used for decision making, only two of them, the upper and lower limits of the speaker´s one octave pitch range, are speaker dependent. However, these two threshold values of a speaker are easily extracted and set by the algorithm from a sample of only 4-5 s duration of his (or her) normal speech.