Method and apparatus for producing natural sounding pitch contours in a speech synthesizer

• US 7,280,969 B2
• Filed: 12/07/2000
• Issued: 10/09/2007
• Est. Priority Date: 12/07/2000
• Status: Expired due to Term

• Current Assignee: Cerence Operating Company (Cerence Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Bakis, Raimo, Eide, Ellen Marie
• Primary Examiner(s): Azad; Abul K.
• Application Number:
  US09/732,122
• Publication Number:
  US 20020072909A1
• Time in Patent Office: 2,497 Days
• Field of Search: 704258-269
• 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

Abstract

A speech synthesis system is disclosed that utilizes a pitch contour resulting in a more natural-sounding speech. The present invention modifies the predicted pitch, b(t), for synthesized speech using a low frequency energy booster. The low frequency energy booster interpolates the discrete pitch values, if necessary, and increase the amount of energy of the pitch contour associated with low frequency values, such as all frequency values below 10 Hertz. The amount of energy of the pitch contour associated with low frequency values can be increased, for example, by adding band-limited noise (a carrier signal) to the pitch contour, b(t), or by filtering the pitch values with an impulse response filter having a pole at the desired low frequency value. The present invention serves to add vibrato to the to the original pitch contour, b(t), and thereby improves the naturalness of the synthetic waveform.

Claims

1. A method for synthesizing speech, comprising:

generating a pitch contour for said synthesized speech; and

enhancing the natural sound of concatenated synthesized speech segments by increasing an amount of energy in low frequency components of said pitch contour.

2. The method of claim 1, wherein said low frequency components are below approximately 10 Hz.

3. The method of claim 1, further comprising the step of interpolating discrete pitch values to generate said pitch contour.

4. The method of claim 1, wherein said increasing step further comprises the step of adding band limited noise to said pitch contour.

5. The method of claim 4, wherein said band limited noise is comprised of one or more sinusoidal components.

6. The method of claim 4, wherein said band limited noise may be expressed as a x sin( ω

t+Φ

), where a is the amplitude of the pitch variation, ω

=2π

f_r; and

f_r is the rate of pitch variation.

7. The method of claim 1, wherein said increasing step further comprises the step of filtering said pitch contour with an impulse response filter having a pole at a desired low frequency value.

8. The method of claim 1, wherein said increasing step serves to add vibrato to said pitch contour.

9. The method of claim 1, wherein said pitch contour comprises a pitch value associated with each syllable of said speech.

10. A method for synthesizing speech, comprising:

generating a pitch contour for said synthesized speech; and

enhancing the natural sound of concatenated synthesized speech segments by adding band limited noise to said pitch contour.

11. The method of claim 10, wherein said band limited noise is added only to low frequency components below approximately 10 Hz.

12. The method of claim 10, further comprising the step of interpolating discrete pitch values to generate said pitch contour.

13. The method of claim 10, wherein said band limited noise is comprised of one or more sinusoidal components.

14. The method of claim 10, wherein said band limited noise may be expressed as a x sin( ω

t+Φ

), where a is the amplitude of the pitch variation, ω

=2π

f_r; and

f_r is the rate of pitch variation.

15. The method of claim 10, wherein said adding step serves to add vibrato to said pitch contour.

16. The method of claim 10, wherein said pitch contour comprises a pitch value associated with each syllable of said speech.

17. A method for synthesizing speech, comprising:

generating a pitch contour for said synthesized speech; and

enhancing the natural sound of concatenated synthesized speech segments by filtering said pitch contour with an impulse response filter having a pole at a desired low frequency value.

18. The method of claim 17, wherein low frequency value is below approximately 10 Hz.

19. The method of claim 17, further comprising the step of interpolating discrete pitch values to generate said pitch contour.

20. The method of claim 17, wherein said increasing step serves to add vibrato to said pitch contour.

21. The method of claim 17, wherein said pitch contour comprises a pitch value associated with each syllable of said speech.

22. A speech synthesizer, comprising:

a pitch predictor that generates a pitch contour for said synthesized speech; and

a low frequency energy booster to enhance the natural sound of concatenated synthesized speech segments by increasing an amount of energy in low frequency components of said pitch contour.

23. The speech synthesizer of claim 22, wherein said low frequency energy booster adds band limited noise to said pitch contour.

24. The speech synthesizer of claim 22, wherein said low frequency energy booster filters said pitch contour with an impulse response filter having a pole at a desired low frequency value.