Apparatus for synthesizing speech by varying pitch

• US 5,787,398 A
• Filed: 08/26/1996
• Issued: 07/28/1998
• Est. Priority Date: 03/18/1994
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Lowry, Andrew
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): MCFADDEN, SUSAN IRIS
• Application Number:
  US08/702,933
• Time in Patent Office: 701 Days
• Field of Search: 704/262, 704/263, 704/264, 704/265, 704/266, 704/267, 704/268
• US Class Current: 704/268
• CPC Class Codes: G10L 13/033 Voice editing, e.g. manipulating the voice of the synthesiser
• CPC Class Codes: G10L 13/0335 Pitch control
• CPC Class Codes: G10L 13/07 Concatenation rules

Abstract

The pitch of synthesized speech signals is varied by separating the speech signals into a spectral component and an excitation component. The latter is multiplied by a series of overlapping window functions synchronous, in the case of voiced speech, with pitch timing mark information corresponding at least approximately to instants of vocal excitation, to separate it into windowed speech segments which are added together again after the application of a controllable time-shift. The spectral and excitation components are then recombined. The multiplication employs at least two windows per pitch period, each having a duration of less than one pitch period. Alternatively each window has a duration of less than twice the pitch period between timing marks and is asymmetric about the timing mark.

Claims

1. A speech synthesis apparatus including means controllable to vary a pitch of speech signals synthesized thereby, having:

(i) means for separating the speech signals into a spectral component and an excitation component;

(ii) means for multiplying the excitation component by a series of overlapping window functions synchronous, in the case of voiced speech, with pitch timing mark information corresponding at least approximately to instants of vocal excitation, to separate it into windowed segments;

(iii) means to apply a controllable time-shift to the segments and add the time-shifted segments together; and

(iv) means for recombining the spectral and excitation components;

wherein the multiplying means employs at least two windows per pitch period, each having a duration of less than one pitch period.

2. A speech synthesis apparatus according to claim 1 in which the windows consist of first windows, one per pitch period, embracing timing mark positions and a plurality of intermediate windows.

3. A speech synthesis apparatus according to claim 2 in which the intermediate windows each have a width less than that of the first windows.

4. A speech synthesis apparatus according to claim 3 comprising:

(a) a store containing items of data each defining a portion of speech signal waveform, and each including timing mark information corresponding at least approximately to a peak of the vocal excitation; and

(b) driver means responsive to signals input thereto to provide addresses to read out items of data from the store and to provide pitch signals representing context-dependent pitch changes to be made to speech.

5. A speech synthesis apparatus according to claim 3 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech and of a filter having the inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal;

and the means for recombining them comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

6. A speech synthesis apparatus according to claim 2 comprising:

(a) a store containing items of data each defining a portion of speech signal waveform, and each including timing mark information corresponding at least approximately to a peak of the vocal excitation; and

(b) driver means responsive to signals input thereto to provide addresses to read out items of data from the store and to provide pitch signals representing context-dependent pitch changes to be made to speech.

7. A speech synthesis apparatus according to claim 2 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech and of a filter having the inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal;

and the means for recombining them comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

8. A speech synthesis apparatus according to claim 1 comprising:

(a) a store containing items of data each defining a portion of speech signal waveform, and each including timing mark information corresponding at least approximately to a peak of the vocal excitation; and

(b) driver means responsive to signals input thereto to provide addresses to read out items of data from the store and to provide pitch signals representing context-dependent pitch changes to be made to speech.

9. A speech synthesis apparatus according to claim 8 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech of and of a filter having the inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal;

and means for recombining them comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

10. A speech synthesis apparatus according to claim 1 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech and of a filter having an inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal; and

the means for recombining the spectral and excitation components comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

12. A speech synthesis apparatus according to claim 4 comprising:

(a) a store containing items of data each defining a portion of speech signal waveform, and each including timing mark information corresponding at least approximately to a peak of the vocal excitation; and

(b) driver means responsive to signals input thereto to provide addresses to read out items of data from the store and to provide pitch signals representing context-dependent pitch changes to be made to speech.

14. A speech synthesis apparatus according to claim 4, in which the compression or expansion means is operable in response to timing mark information including timing marks corresponding at least approximately to instants of vocal excitation to vary a degree of compression or expansion synchronously therewith such that the excitation signal is compressed or expanded less in the vicinity of the timing marks than it is in the center of a pitch period between two consecutive timing marks.

15. A speech synthesis apparatus according to claim 14 comprising:

(a) a store containing items of data each defining a portion of speech signal waveform, and each including timing mark information corresponding at least approximately to a peak of the vocal excitation; and

(b) driver means responsive to signals input thereto to provide addresses to read out items of data from the store and to provide pitch signals representing context-dependent pitch changes to be made to speech.

16. A speech synthesis apparatus according to claim 4 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech and of a filter having the inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal;

and the means for recombining them comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

11. A speech synthesis apparatus including means controllable to vary a pitch of speech signals synthesized thereby, having:

(i) means for separating the speech signals into a spectral component and an excitation component;

(ii) means for controlling pitch of the excitation component by repeating or omitting pitch periods thereof and, respectively, temporally compressing or expanding said component by interpolating new signal samples from input signal samples; and

(iii) means for recombining the spectral and excitation components.

13. A speech synthesis apparatus according to claim 11 in which the means for separating the spectral and excitation components comprises:

(a) analysis means for receiving synthesized speech and generating parameters of a filter having a frequency response similar to the spectral content of the speech and of a filter having the inverse response; and

(b) an inverse filter connected to receive the parameters to filter the speech to produce a residual signal;

and the means for recombining them comprises;

(c) a filter connected to receive the parameters and to filter the residual signal in accordance with the response.

17. A speech synthesis apparatus including means for controlling a pitch of an input signal by multiplying the signal by a series of overlapping windows to separate it into segments and recombining the segments after subjecting the segments to a time shift, the windows being synchronous with timing marks representing instants of peak vocal excitation, wherein each window has a duration of less than twice a pitch period between timing marks and is asymmetric about the timing mark.

18. A speech synthesis apparatus according to claim 17 including means for separating a speech signal into a spectral component and an excitation component, the pitch controlling means being connected to receive the excitation component as said input signal, and means for recombining the spectral component and pitch-adjusted excitation component.

19. A speech synthesis apparatus according to claim 17 wherein each window has a duration of less than 1.7 times the pitch period between timing marks.

20. A speech synthesis apparatus according to claim 19 wherein each window has a duration of between 1.25 and 1.6 times the pitch period between timing marks.

21. A speech synthesis apparatus according to claim 17 wherein each window embraces a complete period between two pitchmarks.