System for improving speech intelligibility through high frequency compression

• US 20060241938A1
• Filed: 12/09/2005
• Published: 10/26/2006
• Est. Priority Date: 04/20/2005
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Hetherington, Phillip A., Li, Xueman
• Granted Patent: US 8,086,451 B2
• Time in Patent Office: Days
• US Class Current: 704/208
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 21/0264 characterised by the type of parameter measurement, e.g. correlation techniques, zero crossing techniques or predictive techniques
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

A speech enhancement system that improves the intelligibility and the perceived quality of processed speech includes a frequency transformer and a spectral compressor. The frequency transformer converts speech signals from the time domain to the frequency domain. The spectral compressor compresses a pre-selected portion of the high frequency band and maps the compressed high frequency band to a lower band limited frequency range.

Claims

1. A speech system that improves the intelligibility and quality of a processed speech, comprising:

a frequency transformer that converts speech signals into a spectrum of frequencies; and

a spectral compressor electrically coupled to the frequency transformer that compresses a pre-selected high frequency band and maps the compressed high frequency band to a lower band limited frequency range.

2. The system of claim 1, where the frequency converter is programmed to automatically converts the speech signal into its frequency spectrum in nearly real time.

3. The system of claim 1, where the frequency converter is programmed or configured to automatically convert the speech signal into the spectrum of frequencies in real time.

4. The system of claim 1, where the high frequency band comprises a larger range of frequencies than the lower band limited frequency range.

5. The system of claim 1 where the spectral compressor comprises a non-linear compression basis function.

6. The system of claim 1 where the lower band limited frequency range comprises a portion of an analog bandwidth.

7. The system of claim 1 where the lower band limited frequency range comprises a portion of a telephone bandwidth.

8. The system of claim 1 further comprising a noise detector configured to detect and measure a level of noise present when the speech signal is detected.

9. The system of claim 1 further comprising a noise detector configured to detect and estimate a level of noise present when the speech signal is detected.

10. The system of claim 1 further comprising a gain controller configured to adjust the gain of the compressed high frequency band in relation to an independent extraneous signal.

11. The system of claim 10 where the independent extraneous signal comprises a background noise.

12. The system of claim 1 further comprising a gain controller coupled to the spectral compressor, where the spectral compressor is configured to adjust substantially only the gain of the compressed high frequency band at the lower band limited frequency range.

13. The system of claim 12 where the spectral compressor is configured to apply a plurality of gain adjustments that varies with a signal independent of the detected speech signal.

14. A speech system that improves the intelligibility of a processed speech, comprising:

a frequency transformer that converts speech signals into its frequency domain;

a spectral compressor coupled to the frequency transformer that compresses a pre-selected high frequency band and maps the compressed high frequency band to a lower frequency band;

a noise detector configured to detect and estimate a level of noise present; and

a gain controller configured to adjust the gain of the compressed high frequency band proportionally to the changing level of an independent and extraneous signal.

15. The speech system of claim 14 further comprising a controller that regulates the spectral compressor, the controller comprising a monitor that compares a signal-to-noise ratio of the compressed signal to a signal-to-noise ratio of the signal before it is compressed.

16. The speech system of claim 14 where the gain controller is configured to apply a gain that varies with a changing level of the extraneous signal.

17. The speech system of claim 14 where the gain controller is configured to apply a variable gain that causes the level of the compressed signal to be substantially coincident with a level of the independent and extraneous signal.

18. A speech system that improves the intelligibility of a processed speech, comprising:

a frequency transformer that converts speech signals from time domain into frequency domain in real time;

a spectral compressor coupled to the frequency transformer that compresses a pre-selected high frequency band and maps the compressed high frequency band to a lower frequency band within a telephone pass band;

a noise detector configured to detect and measure a background noise level of speech signals; and

a gain controller configured to apply a variable gain to the compressed high frequency band in relation to the level of the background noise.

19. The speech system of claim 18 further comprising a controller that regulates the spectral compressor through a communication bus, the controller compares a signal-to-noise ratio of a portion of the detected speech signal to a signal-to-noise ratio of a portion of the compressed signal.

20. The speech system of claim 19 where the controller is programmed to compare amplitude through a comparison of frequency bins.

21. The speech system of claim 19 further comprising an automatic speech recognition system coupled to the gain controller.