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.