C. A. McGonegal

An approach to the approximation problem for nonrecursive digital filters

A direct design procedure for nonrecursive digital filters, based primarily on the frequency-response characteristic of the desired filters, is presented. An optimization technique is used to minimize the maximum deviation of the synthesized filter from the ideal filter over some frequence range. Using this frequency-sampling technique, a wide variety of low-pass and bandpass filters have been designed, as well as several wide-band differentiators. Some experimental results on truncation of the filter coefficients are also presented. A brief discussion of the technique of nonuniform sampling is also included.

Comparative performance study of several pitch detection algorithms

A comparative performance study of five pitch detection algorithms was conducted. A speech data base, consisting of eight utterances spoken by three males, three females, and one child was constructed. Both telephone and wideband recordings were made of each of the utterances. For each of the utterances in the data base a “standard” pitch contour was semiautomatically measured using a highly sophistocated interactive pitch detection program. The “standard” pitch contour was then compared with the pitch contour that was obtained from each of the five programmed pitch detectors. The algorithms used in this study were (1) a center clipping, infinite‐peak clipping, modified autocorrelation method; (2) the cepstral method; (3) the SIFT method; (4) the parallel processing time domain method; and (5) the data reduction method. A set of measurements were made on the pitch contours to quantify the various types of errors which occur in each of the above methods. Included among the error measurements were the avera...

On reducing the buzz in LPC synthesis

A method for reducing the characteristic buzz of LPC synthetic speech is presented. The method consists of the use of a nonimpulse source for exciting the LPC synthesizer during voiced sounds. One novel feature is that the temporal parameters of the source are kept in fixed proportion to the pitch period. An extensive perceptual experiment has shown that the resulting quality of the synthesis is significantly preferred over the quality of the standard LPC synthesis.

A semiautomatic pitch detector (SAPD)

The purpose of this paper is to describe a technique for semiautomatically determining the pitch contour of an utterance. The method is significantly more sophisticated than the standard technique of hand tracking of pitch periods from a waveform display of the utterance and leads to a fairly robust measurement of the pitch period. This technique utilizes a simultaneous display (on a 10 ms section-by-section basis) of the low-pass filtered waveform, the autocorrelation of a 400- point segment of the low-pass filtered waveform, and the cepstrum of the same 400-point segment of the wideband recording. For each of the separate displays (i.e., waveform, autocorrelation, and cepstrum) an independent estimate of the pitch period is made on an interactive basis with the computer, and the final pitch period decision is made by the user based on results of each of the measurements. The technique has been tested on a large number of utterances spoken by a variety of speakers with very good results. Formal tests of the method were made in which four people were asked to use the method on three different utterances, and their results were then compared. During voiced regions, the standard deviation in the value of the pitch period was about 0.5 samples across the four people. The standard deviation of the location of the time at which voiced regions became unvoiced, and vice versa was on the order of half a section duration, or 5 ms. The major limitation of the proposed method is that it requires about 30 min to analyze 1 s of speech. However, the increased accuracy and robustness of the results indicate that the tradeoff of time for accuracy is a good one for many applications.

A subjective evaluation of pitch detection methods using LPC synthesized speech

A subjective evaluation of seven pitch detectors has been carried out using synthetic speech. The evaluation is intended to complement the objective performance evaluation of the same pitch detection algorithms in the investigation of Rabiner et al. [1]. In the earlier study, each of the seven algorithms was evaluated on the basis of its performance with respect to four different types of errors. The standard of comparison was a semiautomatically determined pitch contour of each utterance in the experimental corpus. In the present study, the quality of LPC (linear predictive coding) analyzed and synthesized speech was evaluated. The pitch contour used in the synthesis was obtained either from one of the seven pitch detectors or from the semiautomatic pitch analysis. Using a computer-controlled sort board, an experiment was run in which each of eight listeners was asked to rank the nine versions of each utterance (the natural version was included to provide a stable anchor point). Results are presented on the overall preference for each pitch detector. In addition, subject preference as a function of the pitch range of the speaker and the transmission environment used in the recording is discussed. The present results are compared to those obtained in the earlier objective performance study.

The effects of ADPCM coding and LPC vocoding on an automatic speaker verification system

In an earlier report [C. A. McGonegal et al., J. Acoust. Soc. Am. 62, S4(A) (Fall 1977).] the effects of several transmission systems on speaker verification by human listeners were investigated. There it was shown that the transmission system played a significant role in the speaker verification process. In this talk we show the effects of the transmission system on an existing automatic speaker verification system [A. E. Rosenberg, Bell Systems Technical Journal 55, 723–744 (1976)] in which the measured features are pitch and gain as a function of time for a specified utterance. There were ten male and ten female customers and 40 male and 40 female imposters in this experiment. All utterances were recorded using a conventional telephone connection. Post processing included ADPCM coding and LPC vocoding. Preliminary results indicate that, on the average, the transmission system affects the verification accuracy, especially when the reference and test utterances are subjected to different transmission conditions.

Perceptual evaluation of several pitch detection algorithms

Recently an objective performance evaluation of seven pitch detection algorithms was made by Rabiner et al. [IEEE Trans. Acoust. Speech Signal Process., Oct. (1976)]. Each of the seven algorithms was compared on the basis of its performance with respect to five different types of errors. The standard of comparison was a semiautomatically determined pitch contour of each utterance. To complement this investigation we describe the results of a subjective evaluation of the synthetic speech quality of LPC analyzed and synthesized speech. The pitch contour used in the synthesis was either one of the seven pitch contours or the result of the semiautomatic analysis. Using a computer controlled sort board, an experiment was run in which each of eight listeners was asked to rank the nine versions of each utterance (the natural version was included to provide a stable anchor point). Results are presented on the over‐all preference for each pitch detector. In addition, subject preference as a function of the pitch r...