Pitch determiner for a speech analyzer

• US 6,018,706 A
• Filed: 12/29/1997
• Issued: 01/25/2000
• Est. Priority Date: 01/26/1996
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Li, Xiaojun, Huang, Jian-Cheng, Simpson, Floyd
• Primary Examiner(s): Dorvil, Richemond
• Application Number:
  US08/999,171
• Time in Patent Office: 757 Days
• Field of Search: 704/223, 704/205, 704/206, 704/207, 704/208, 704/222, 704/219, 704/220, 704/200
• US Class Current: 704/207
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 21/013 Adapting to target pitch
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A pitch determiner (414) for use with a speech analyzer includes a pitch function generator (414) which generates a plurality of pitch components representing a pitch function for one or more sequential segments of speech. which are represented by a predetermined number of digitized speech samples. A pitch enhancer (1116) enhances the pitch function of a current segment of speech utilizing the pitch function of one or more sequential segments of speech to generate a plurality of enhanced pitch components. A pitch detector (1118) detects the pitch of the current segment of speech by determining the pitch of an enhanced pitch component having a largest amplitude of the plurality of enhanced pitch components.

Claims

1. A pitch determiner for use with a speech analyzer for determining a pitch within one or more sequential segments of speech, each segment of speech being represented by a predetermined number of digitized speech samples, said pitch determiner comprising:

a pitch function generator for generating from the predetermined number of digitized speech samples, a plurality of pitch components representing a pitch function, wherein said pitch function defines an amplitude of each of the plurality of pitch components;

a pitch enhancer, for enhancing the pitch function of a current segment of speech utilizing the pitch function of one or more sequential segments of speech, by generating a plurality of enhanced pitch components; and

a pitch detector for detecting the pitch of the current segment of speech by determining the pitch of an enhanced pitch component having a largest amplitude of the plurality of enhanced pitch components.

2. The pitch determiner of claim 1, further comprising a digital filter, coupled to an input of said pitch function generator, for limiting a spectrum of the segment of speech to an anticipated range of pitch components.

3. The pitch determiner of claim 1, further comprising one or more delay elements for generating the pitch function of one or more sequential segments of speech.

4. The pitch determiner of claim 1, wherein said pitch function generator comprises:

a squarer for squaring each of the predetermined number of digitized speech samples representing a segment of speech to generating squared digitized speech samples;

Fast Fourier Transform (FFT) calculator for deriving frequency components corresponding to the predetermined number of squared digitized speech samples representing a segment of speech;

an absolute value calculator for calculating an absolute value of the frequency components derived by tb FFT calculator; and

an Inverse Fourier Transform (IFFT) calculator for deriving a plurality of pitch components from the frequency components derived by the FFT calculator.

5. The pitch determiner according to claim 4, further comprising a haar filter, coupled to said squarer and to said FFT calculator, for emphasizing glottal events embedded in the speech thereby increasing accuracy of pitch detection.

6. The pitch determiner according to claim 4, further comprising a band limiting filter, coupled to said FFT calculator and to said absolute value calculator, for limiting the range of the frequency components derived by the FFT.

7. The pitch determiner according to claim 4, further comprising a normalizer, coupled to said IFFT calculator for normalizing each pitch component of said plurality of pitch components derived therefrom.

8. The pitch determiner according to claim 1, wherein said pitch enhancer comprises a dynamic peak enhancer for generating a plurality of enhanced pitch components from a plurality of pitch components, said dynamic peak enhancer being programmed to perform the steps of:

(a) selecting a first pitch component of a first pitch function, the first pitch component having an amplitude;

(b) determine a range of pitch components about a pitch component of a second pitch function corresponding to the first pitch component selected

(c) selecting a second pitch component having a maximum amplitude from within the range of pitch components;

(d) summing the amplitude of the first pitch component with the maximum amplitude of the second pitch component to generate an enhanced pitch component; and

repeating said steps of (a) through (d) for a predetermined number of pitch components of the plurality of pitch components of the first pitch function, to generate the plurality of enhanced pitch components.

9. The pitch determiner according to claim 8, wherein the first pitch function represents the pitch function of the current segment of speech, and wherein the second pitch function represents the pitch function of a succeeding segment of speech.

10. The pitch determiner according to claim 1, wherein the pitch within the segment of speech represents a first pitch candidate and wherein a largest amplitude of the plurality of enhanced pitch component represents a first magnitude, and wherein said pitch determiner further comprises:

a second pitch detector for detecting a second pitch of the current segment of speech having a current magnitude, by utilizing a pitch of a preceding segment of speech and the pitch function of the current segment of speech, the second pitch detected representing a second pitch candidate;

a summer for summing the current magnitude and magnitudes of selected pitch components for one or more preceding segments of speech to generate a second magnitude, the selected pitch components for each of the one or more preceding segments of speech being determined by the pitch function and pitch of a preceding segment of speech; and

a candidate selector for selecting the first pitch candidate when a ratio of the first magnitude and the second magnitude is less than a threshold, and selecting the second pitch candidate when a ratio of the first magnitude and second magnitude is greater than or equal to the threshold.

11. The pitch determiner according to claim 10, wherein the threshold is calculated.