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.]

In this paper, we describe a real-time all-digital spectrum channel vocoder implemented on a programmable signal processor. The vocoder system efficiently utilizes a radix four, 64-point FFT algorithm for spectral analysis, while the pitch extractor selects the pitch period using decision logic on the average magnitude difference function (AMDF) of the input speech. The receiver linearly interpolates both the pitch period and the synthesized impulse response which is generated by using the inverse Fourier transform. The vocoder frame updating rate is 22 msec, and the input speech sampling rate is 7040 samples/sec. The configuration of the vocoder and the logic of the AMDF pitch extractor is discussed and the system demonstrated with audio tapes.