GAIN AND SPECTRAL SHAPE ADJUSTMENT IN AUDIO SIGNAL PROCESSING

• US 20090225980A1
• Filed: 10/07/2008
• Published: 09/10/2009
• Est. Priority Date: 10/08/2007
• Status: Active Grant

• Current Assignee: Cerence Inc., Cerence Operating Company (Cerence Inc.)
• Original Assignee: Nuance Communications, Inc. (Microsoft Corporation)
• Inventors: Schmidt, Gerhard Uwe, Iser, Bernd
• Granted Patent: US 8,565,415 B2
• Time in Patent Office: Days
• US Class Current: 379/406.20
• CPC Class Codes: G10L 2021/02082 the noise being echo, reverberation of the speech
• CPC Class Codes: H04M 1/6075 adapted for handsfree use in a vehicle H04M1/6058 takes precedence; arrangements for holding telephones in a vehicle B60R11/0241
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A signal processing system enhances communication. When an audio signal is detected, an echo component of the detected audio signal may be estimated. A near party communication device may receive an audio signal from a remote party communication device. A characteristic of the received audio signal may be adjusted based on the echo component of the detected audio signal.

Claims

1. A method for processing an audio signal, comprising:

estimating an echo component of an audio signal detected at a near party communication device;

receiving an audio signal transmitted from a remote party communication device to the near party communication device; and

adjusting a characteristic of the received audio signal based on the echo component of the detected audio signal.

2. The method of claim 1, where the act of adjusting the characteristic of the received audio signal comprises adjusting a gain of the received audio signal based on the echo component of the detected audio signal.

3. The method of claim 1, where the act of adjusting the characteristic of the received audio signal comprises adjusting a spectral shape of the received audio signal based on the echo component of the detected audio signal.

4. The method of claim 3, where the act of adjusting the spectral shape comprises modifying a frequency envelope of the received audio signal based on the echo component of the detected audio signal.

5. The method of claim 1, where the echo component of the detected audio signal is due to a loudspeaker output of an audio signal received from the remote party communication device.

6. The method of claim 1, where the near party communication device is associated with a microphone and a loudspeaker, where the detected audio signal comprises a microphone signal generated by the microphone;

and

where the act of estimating the echo component comprises analyzing the microphone signal to identify a portion of the microphone signal that is due to the loudspeaker outputting an audio signal received from the remote party communication device.

7. The method of claim 1, further comprising estimating a noise component of the detected audio signal;

and

where the act of adjusting the characteristic of the received audio signal comprises adjusting a gain or spectral shape of the received audio signal based on the echo component and the noise component of the detected audio signal.

8. The method of claim 1, where the act of adjusting the characteristic of the received audio signal comprises:

modeling a desired spectral shape with an infinite impulse response filter to obtain a first model result;

modeling the desired spectral shape with a finite impulse response filter to obtain a second model result;

comparing the first model result with the second model result;

selecting the infinite impulse response filter to adjust a spectral shape of the received audio signal when the first model result is a better match for the desired spectral shape; and

selecting the finite impulse response filter to adjust the spectral shape of the received audio signal when the second model result is a better match for the desired spectral shape.

9. The method of claim 1, where the act of adjusting the characteristic of the received audio signal comprises:

passing the received audio signal through an infinite impulse response filter to adjust a spectral shape of the received audio signal based on an inverse discrete Fourier transform of a squared magnitude of a desired spectral shape;

or

passing the received audio signal through a finite impulse response filter to adjust the spectral shape of the received audio signal based on an inverse discrete Fourier transform of an inverse of a squared magnitude of the desired spectral shape.

10. The method of claim 1, where the act of adjusting the characteristic of the received audio signal comprises adjusting a gain or spectral shape of the received audio signal based on an average peak echo-to-noise ratio of the detected audio signal.

11. The method of claim 10, where the average peak echo-to-noise ratio is smoothed in frequency by an infinite impulse response filter.

12. A method for audio signal processing, comprising:

receiving an audio signal at a near party communication device that was transmitted from a remote party communication device;

estimating local background noise at the near party communication device;

estimating local acoustic echo at the near party communication device; and

adjusting a gain of the received audio signal based on the estimated local background noise and the estimated local acoustic echo.

13. The method of claim 12, where the local acoustic echo is due to a loudspeaker output of an audio signal received from the remote party communication device.

14. The method of claim 12, further comprising adjusting a spectral shape of the received audio signal based on the estimated local background noise and the estimated local acoustic echo.

15. The method of claim 14, where a desired spectral shape is modeled by both an infinite impulse response filter and a finite impulse response filter, the model results of both filters are compared with each other for each frame, and for each frame the model result that better matches the desired spectral shape is used for the adjusting of the spectral shape of the received audio signal.

16. The method of claim 14, where the spectral shape of the received audio signal is adjusted by an infinite impulse response filter based on an inverse discrete Fourier transform of a squared magnitude of a desired spectral shape or a finite impulse response filter based on an inverse discrete Fourier transform of an inverse of a squared magnitude of the desired spectral shape.

17. The method of claim 14, where the gain or spectral shape of the received audio signal is adjusted based on an average peak echo-to-noise ratio of the detected audio signal.

18. A signal processing system, comprising:

an echo compensation filter configured to filter an audio signal detected at a near party communication device and output an estimate of an echo component of the detected audio signal; and

a signal adjustment unit coupled with the echo compensation filter and configured to receive an audio signal from a remote party communication device, where the signal adjustment unit is configured to adjust a characteristic of the received audio signal based on the echo component of the detected audio signal.

19. The system of claim 18, where the echo component of the detected audio signal is due to a loudspeaker output of an audio signal received from the remote party communication device.

20. The system of claim 18, further comprising a noise reduction filter configured to filter the detected audio signal and output an estimate of a noise component of the detected audio signal;

and

where the signal adjustment unit is configured to adjust a gain or spectral shape of the received audio signal based on the echo component and the noise component of the detected audio signal.

21. The system of claim 18, where the signal adjustment unit comprises a finite impulse response filter or an infinite impulse response filter configured to adjust a spectral shape of the received audio signal.

22. The system of claim 18, where the signal adjustment unit is configured to adjust a gain or spectral shape of the received audio signal based on an average peak echo-to-noise ratio of the detected audio signal.

23. The system of claim 18, where the detected audio signal comprises a microphone signal, the system further comprising:

a first analysis filter bank configured to divide the microphone signal into microphone sub-band signals;

a second analysis filter bank configured to divide a reference signal into reference sub-band signals to be input into the echo compensation filter to reduce echo in the microphone sub-band signals; and

a synthesis filter bank configured to synthesize the microphone sub-band signals filtered by the echo compensation filter.

24. The system of claim 18, further comprising a transmitter configured to transmit the detected audio signal filtered by the echo compensation filter to a remote party communication device.

25. The system of claim 18, further comprising an amplifier, where the echo compensation filter is configured to receive a reference signal for adaptation of echo compensation filter coefficients either before or after amplification of the received audio signal processed by the signal adjustment unit.

26. A signal processing system, comprising:

a loudspeaker configured to output a loudspeaker signal;

a microphone configured to convert sound into an operational signal;

a noise reduction filter configured to filter the operational signal and output an estimate of noise;

an echo compensation filter configured to filter the operational signal and output an estimate of echo; and

a signal adjustment unit in communication with the noise reduction filter and the echo compensation filter, where the signal adjustment unit is configured to receive an audio signal from a remote party communication device and adjust a gain or spectral shape of the received audio signal based on the estimate of noise and the estimate of echo.

27. The system of claim 26, where the echo in the operational signal is due to detection of the loudspeaker signal at the microphone, where the loudspeaker signal is based on an audio signal received from the remote party communication device.

28. The system of claim 26, where the microphone comprises a directional microphone of a microphone array, further comprising a beamformer configured to receive the operational signal from the microphone array and obtain a beamformed signal.