Real-Time Digital-Cepstrum-Pitch Extraction on a 12-Bit Machine

Abstract

This paper describes a digital cepstrum-pitch detector designed to work in real time on a 12-bit binary machine. Spectrum and cepstrum analysis of raw speech data is accomplished through the use of a single complex Fast Fourier Transform (FFT) algorithm. Pitch detection is accomplished by a cepstrum-peak scanning logic designed to locate the position of a peak corresponding to the pitch period. Since other peaks may exist in the data, logic is required to differentiate these peaks from the desired one. Because of the limited word size of the machine, special processing algorithms were developed to perform logging and to avoid the squaring of variables. Various logical operations performed on the spectrum and cepstrum functions in voicing detection and in the extraction of pitch are presented and discussed. A demonstration of the performance of this pitch detector when operated with a 2400-bit/sec digital vocoder will be presented by means of a tape recording. [Work supported under contract.]