SPEECH SIGNAL PITCH DETECTOR USING PREDICTION ERROR DATA

• US 3,740,476 A
• Filed: 07/09/1971
• Issued: 06/19/1973
• Est. Priority Date: 07/09/1971
• Status: Expired due to Term

• Current Assignee: Bishnu Saroop Atal
• Original Assignee: Bishnu Saroop Atal
• Inventors: Atal, Bishnu Saroop
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US05/161,173
• Time in Patent Office: 711 Days
• Field of Search: 179/1SA,15.55R 325/38A
• US Class Current: 704/207
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence

Abstract

Pitch periods in a complex speech signal are determined by evaluating the error in predicting the value of a sample of the signal on the basis of past sample values, and by locating samples for which the prediction error is large. Advantageously, the prediction error signal is devoid of all formant structure, so that there is no chance of confusing pitch signal peaks with formant peaks. A voiced-unvoiced decision is obtained from the ratio of the mean-squared value of the speech signal to the meansquared value of the prediction error signal.

Claims

1. A signal analyzer for determining the fundamental period of a speech signal, which comprises, adaptive predictor means supplied with samples of said speech signal for predicting the present value of each sample on the basis of a weighted summation of a number of prior sample values of said speech signal, means for subtracting said predicted speech value from the actual speech value to develop a difference signal, and means for determining the fundamental frequency of said difference signal as an indication of the fundamental period of said speech signal.

2. A signal analyzer as defined in claim 1, wherein said means for determining the fundamental frequency of said difference signal comprises, means for determining the frequency of occurrence of difference signal maxima above a prescribed threshold.

3. A signal analyzer as defined in claim 1, wherein said means for determining the fundamental frequency of said difference signal comprises, means for autocorrelating said difference signal for developing an autocorrelation signal representative of the periodic character of said difference signal, and means for detecting the location of the peak value of said autocorrelation signal.

4. Apparatus for determining the fundamental period of a speech signal, which comprises, means for developing an estimate of the present value of a speech signal on the basis of past values of said speech signal, means for developing a signal representative of the difference between said signal estimate and the true present value of said speech signal, and means for determining the fundamental frequency of said difference signal to develop a signal representative of the fundamental period of said speech signal.

5. Apparatus for determining the fundamental period of a speech signal, which comprises, adaptive predictor means supplied with samples of said speech signal for developing an estimate of the momentary value of said speech signal from previously supplied samples, means for developing a prediction error signal from the difference between said predicted signal estimate and the corresponding momentary value of samples of said speech signal, means for identifying prediction error samples whose magnitudes are above a prescribed threshold, and means for utilizing the frequency of occurrence of said identified error samples as a measure of the fundamental period of said speech signal.

6. Apparatus for analyzing the character of a speech signal, which comprises, in combination, predictor means supplied with samples of a speech signal for developing an estimate of the momentary value of said signal from previously supplied samples, means for developing prediction error signal samples from the difference between samples of said signal estimate and the corresponding momentary value of samples of said speech signal, means for identifying prediction error samples whose magnitudes are above a prescribed threshold, means for developing a first signal proportional to the mean-squared value of said speech samples, means for developing a second signal proportional to the mean-squared value of corresponding ones of said error samples, means for developing a signal proportional to the ratio of said first to said second mean-squared signals, means for utilizing the frequency of occurrence of said identified threshold error samples as a measure of the fundamental period of said speech signal, and means for utilizing said ratio of first and second mean-squared signals as a measure of the voicing characteristic of said speech signal.

7. Apparatus for analyzing the character of a speech signal as defined in claim 6, wherein, values of said ratio of mean-squared signals equal to or greater than a prescribed threshold are used to classify said speech signal as voiced, and wherein values of said ratio of mean-squared signals less than said threshold are used to classify said speech signal as unvoiced.

8. In a pitch analysis arrangement for speech signals, the combination of, means for developing a signal representative of the formant structure of an applied speech signal, means for removing said formant representative signal from said speech signal to produce a signal essentially devoid of all formant information, means for measuring tHe period of said formant devoid signal, and means for determining the voicing character of said speech signal on the basis of the power in said speech signal and the power in said formant devoid signal.