Formant tracker

• US 4,424,415 A
• Filed: 08/03/1981
• Issued: 01/03/1984
• Est. Priority Date: 08/03/1981
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Lin, Kun-Shan
• Primary Examiner(s): Kemeny, Emanuel S.
• Application Number:
  US06/289,603
• Time in Patent Office: 883 Days
• Field of Search: 179/1.5 A, 179/1.5 B, 179/1.5 C, 179/1.5 D, 179/15.55 R, 179/15.55 T, 364/513, 364/725, 364/728, 324/77 B, 324/77 G
• US Class Current: 704/209
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/0018 Speech coding using phonetic or linguistical decoding of the source; Reconstruction using text-to-speech synthesis

Abstract

A formant tracker for receiving an analog speech signal and generating indicia representative of the formant. A pitch tracker determines the fundamental frequency of the analog speech input. The fundamental frequency is used to control a sinusoidal oscillator in the generation of a sinusoidal signal which when combined with the analog speech input generates a convolution over the chosen formant frequency. The process is repeated for each integer multiple of the fundamental frequency, thereby changing the sinusoidal oscillator. The optimal integer multiple is chosen which generates the formant identification. The optimal integer is also used to generate an appropriate bandwidth. Three formant frequency ranges are used to define human speech. The optimal integers for the other two formant identifications and the appropriate bandwidths are similarly determined. The three optimal integer values are combined with the fundamental frequency to get the three formant values and their associated bandwidths. These formant values and their bandwidths together with the fundamental frequency are communicated as output so as to identify in formant form the analog signal.

Claims

1. A formant tracker for receiving an analog signal, said formant tracker comprising:

means for tracking a pitch associated with the analog signal and generating a fundamental frequency therefrom; and

means operably coupled to the output of said pitch tracking means for receiving the fundamental frequency of the analog signal to determine at least one formant within a frequency spectrum in which the analog signal is found, said formant determining means including

means establishing an integer set including a plurality of integers associated with at least a selected frequency range containing said at least one formant and within said frequency spectrum in which the analog signal is found, and

means for establishing within said integer set over the plurality of integers contained therein an optimal integer for said selected frequency range within said frequency spectrum from said integer set and a bandwidth associated with said optimal integer;

said formant determining means generating said at least one formant in response to the product of said optimal integer and said fundamental frequency.

2. A formant tracker as set forth in claim 1, wherein said means for establishing an optimal integer comprises:

means for iteratively generating for each of said plurality of integers within said integer set a sinusoidal signal from said fundamental frequency as multiplied by successive ones of said integers during respective iterations,

means for convolving said sinusoidal signal with said analog signal over the selected frequency range containing said at least one formant and within said frequency spectrum in which the analog signal is found to obtain a convolution having a variable amplitude, and

means for choosing said optimal integer based upon the maximum amplitude of said convolution.

3. A formant tracker as set forth in claim 2, wherein said means for convolving said sinusoidal signal with said analog signal comprises integrating means for integrating the product of said sinusoidal signal and said analog signal over the selected frequency range containing said at least one formant and within said frequency spectrum in which the analog signal is found.

4. A formant tracker for receiving an analog signal, said formant tracker comprising:

means for tracking a pitch associated with the analog signal and generating a fundamental frequency therefrom;

means operably coupled to the output of said pitch tracking means for receiving the fundamental frequency of the analog signal to determine a plurality of formants within a frequency spectrum in which the analog signal is found, said formant determining means including

means establishing respective integer sets each of which includes a plurality of integers and associated with different selected frequency ranges containing respective formants and within said frequency spectrum in which the analog signal is found, and

means for establishing within each said integer set over the plurality of integers contained therein an optimal integer for said selected frequency range corresponding thereto within said frequency spectrum from said respective integer set and a bandwidth associated with each said optimal integer;

said formant determining means generating said plurality of formants in response to the respective products of each of said optimal integers and said fundamental frequency.

5. A formant tracker as set forth in claim 4, wherein

said integer set establishing means is effective to establish three respective integer sets each of which includes a plurality of integers and associated with three different selected frequency ranges containing respective formants and within said frequency spectrum in which the analog signal is found, and

said optimal integer establishing means being effective to establish three optimal integers for said three different selected frequency ranges, such that said formant determining means generates three formants in response to the respective products of each of said three optimal integers and said fundamental frequency.

6. A formant tracker as set forth in claim 5, wherein said three different selected frequency ranges within said frequency spectrum in which the analog signal is found comprise the respective ranges 200-850 hertz, 850-2500 hertz, and 2500-3500 hertz.

7. A formant tracker as set forth in claim 6, wherein said three different selected frequency ranges within said frequency spectrum in which the analog signal is found effectively define human speech.

8. A formant tracker as set forth in claim 7, further including automatic gain control circuit means connected to the input of said pitch tracking means for receiving a speech signal and generating the analog signal therefrom for input to said pitch tracking means.

9. Apparatus for generating indicia representative of an analog signal corresonding to human speech, wherein the indicia includes a plurality of formants within different selected frequency ranges of the analog signal, with each of said formants being contained within a different one of said selected frequency ranges and said formants collectively being definitive of human speech, said apparatus comprising:

means for determining a fundamental frequency from said analog signal;

plural formant determining means operably coupled to the output of said fundamental frequency determining means for respectively identifying individual formants within the frequency spectrum in which the analog signal is found as contained within said different selected frequency ranges, each of said formant determining means including

means establishing a respective integer set including a plurality of integers associated with a selected frequency range containing a respective formant and within said frequency spectrum in which the analog signal is found, said selected frequency range being different from the selected frequency ranges of the other formant determining means,

means for iteratively generating for each of said plurality of integers within said integer set a sinusoidal signal from said fundamental frequency as multiplied by successive ones of said integers during respectively iterations,

means for convolving said sinusoidal signal with said analog signal over the respective selected frequency range containing said formant to obtain a convolution having a variable amplitude, and

means for choosing an optimal integer for said selected frequency range based upon the maximum amplitude of said convolution;

each of said formant determining means generating a respective one of said plurality of formants in response to the respective products of each of said optimal integers and said fundamental frequency; and

means for determining respective bandwidths associated with each of said plurality of formants; and

output means operably coupled to said fundamental frequency determining means, said plural formant determining means, and said bandwidth determining means for providing said plurality of formants and said bandwidths respectively associated therewith along with said fundamental frequency as indicia representative of said analog signal.

10. Apparatus as set forth in claim 9, wherein said means for convolving said sinusoidal signal with said analog signal for each of said formant determining means comprises integrating means for integrating the product of said sinusoidal signal and said analog signal over the respective selected frequency ranges associated with each of said formant determining means.

11. Apparatus as set forth in claim 10, wherein said means for iteratively generating a sinusoidal signal for each of said formant determining means includes a sinusoidal oscillator connected to the output of said fundamental frequency determining means.

12. Apparatus as set forth in claim 11, wherein said fundamental frequency determining means comprises a pitch tracker.

13. Apparatus as set forth in claim 12, wherein three formant determining means are provided respectively corresponding to three different selected frequency ranges 200-850 hertz, 850-2500 hertz, and 2500-3500 hertz.

14. A method of identifying a formant from an analog signal, said method comprising:

generating a fundamental frequency of the analog signal by tracking a pitch associated with said analog signal;

establishing an integer set including a plurality of integers associated with at least a selected frequency range containing at least one formant and within a frequency spectrum in which the analog signal is found;

determining an optimal integer within said integer set from the plurality of integers contained therein for said selected frequency range within said frequency spectrum; and

generating said at least one formant by obtaining the product of said optimal integer and said fundamental frequency.

15. A method as set forth in claim 14, wherein said optimal integer is determined by

iteratively generating for each of said plurality of integers within said integer set a sinusoidal signal from said fundamental frequency as multiplied by successive ones of said integers during respective iterations;

convolving said sinusoidal signal with said analog signal over the selected frequency range containing said at least one formant and within said frequency spectrum in which the analog signal is found to obtain a convolution having a variable amplitude; and

choosing the optimal integer based upon the maximum amplitude of said convolution.

16. A method as set forth in claim 15, wherein a plurality of formants are identified from the analog signal, including

establishing a plurality of different selected frequency ranges each of which contains a respective formant wherein all of said selected frequency ranges lie within said frequency spectrum in which the analog signal is found;

establishing an integer set including a plurality of integers for each of the different selected frequency ranges containing respective formants;

determining an optimal integer for each of said integer sets and corresponding to the respective different selected frequency ranges; and

generating a plurality of formants by obtaining the respective products of each of said optimal integers and said fundamental frequency.