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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.]

A system for the analysis and synthesis speech is described. In the analyzer, speech sounds are first classified into nonturbulent and turbulent groups. The first three formants of the former group and the first three moments of the latter group constitute six significant parameters of speech spectra. By measuring the zero‐crossing densities and/or envelopes of automatically selected frequency bands, these parameters or their equivalents are extracted. To test the feasibility of using these parameters in a speech compression system, a synthesis procedure is carried out. The synthesized speech and its spectrograms are demonstrated. [The research in this paper has been made possible through support and sponsorship extended by the Electronics Research Directorate of the Air Force Cambridge Research Center, under Contract No. AF 19(604)‐1039, Item I.]

In this paper, an experiment is described in which articulation scores were measured as the number of transmitted spectral parameters was varied from 6 to 16 in a Laguerre autocorrelation vocoder. The transmitted spectral parameters were the expansion coefficients of the short‐time‐averaged speech autocorrelation function in terms of Laguerre functions. Thus, these parameters are the same as the expansion coefficients of the speech power spectrum in terms of the Fourier cosine transforms of the Laguerre functions. The analysis and synthesis filters in this vocoder were synthesized from a number of identical RC transistor circuits. The time constant of the Laguerre analysis and synthesis filters was 125×10−6 sec. The system was operated in an analog back‐to‐back mode for these tests. The results presented show that about 16 parameters are required to achieve performance comparable to contemporary filter‐bank vocoders. The intelligibility tests were performed by Bolt Beranek and Newman Inc., in early 1965.