System for equalizing an acoustic signal

• US 8,098,848 B2
• Filed: 05/16/2007
• Issued: 01/17/2012
• Est. Priority Date: 05/19/2006
• Status: Active Grant

• Current Assignee: Cerence Inc., Cerence Operating Company (Cerence Inc.)
• Original Assignee: Nuance Communications, Inc. (Microsoft Corporation)
• Inventors: Haulick, Tim, Schmidt, Gerhard Uwe, Buck, Markus
• Primary Examiner(s): Faulk, Devona
• Assistant Examiner(s): Paul, Disler
• Application Number:
  US11/749,678
• Publication Number:
  US 20080031471A1
• Time in Patent Office: 1,707 Days
• Field of Search: 381/86, 381/103, 381/83, 381/98, 381/93, 381/66, 379/406.01, 37940605-40606, 37940608-40609
• US Class Current: 381/103
• CPC Class Codes: H03G 3/32 the control being dependent upon ambient noise level or sound level
• CPC Class Codes: H03G 5/16 Automatic control
• CPC Class Codes: H04R 2499/13 Acoustic transducers and sound field adaptation in vehicles
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

An equalization system enhances the quality of communications between a remote party and a local party. The equalization system includes an equalization filter that equalizes an acoustic signal received from the remote party. The equalized acoustic signal is transmitted to a speaker based on the equalized acoustic signal. A device converts sound into electrical signals. The electrical signals are transmitted to an echo compensation filter that compensates for reflected sound. Filter characteristics of the equalization filter are based on filter characteristics of the echo compensation filter.

Claims

1. A system for equalizing an acoustic input signal, comprising

an echo compensation filter configured to receive a microphone signal from a microphone, the echo compensation filter comprising multiple echo compensation filter coefficients determined on the basis of the microphone signal;

an equalization filter in communication with the echo compensation filter, the equalization filter configured to equalize the acoustic input signal, where the equalization filter comprises multiple equalization filter coefficients determined based on the echo compensation filter coefficients; and

a reference filter comprising reference filter coefficients that represent a predetermined reference frequency response of the system including the echo compensation fiter and the equalization filter, where the echo compensation filter coefficients are determined based on the reference filter coefficients.

2. The system of claim 1, where the equalization filter is configured to transmit the equalized acoustic input signal to a speaker, and where the microphone signal is generated based on a speaker signal output by the speaker and detected by the microphone.

3. The system of the claim 2, further comprising a speaker amplifier in communication with the speaker and a microphone amplifier in communication with the microphone.

4. The system of claim 3, where at least one of the speaker amplifier and microphone amplifier are configured to be controlled by a user.

5. The system of claim 1, where the echo compensation filter is an adaptive filter.

6. The system of claim 5, where the echo compensation filter comprises a predictive pre-filter.

7. The system of claim 5, where the adaptive filter is an FIR filter.

8. The system of claim 7, where the FIR filter is adapted by a normalized least means square method.

9. The system of claim 1, further comprising a pre-filter, the pre-filter comprising:

filter coefficients determined for modeling a transfer function of the microphone;

and

where the pre-filter is configured to;

receive the equalized acoustic input signal;

generate a pre-filter signal based on the equalized acoustic input signal and on the transfer function of the microphone; and

transmit the pre-filter signal to the echo compensation filter.

10. The system of claim 9, where the microphone is a directional microphone located in an enclosure, and where the filter coefficients of the pre-filter are determined for modeling the transfer function of the directional microphone in a direction of a speaker that is located closer to the directional microphone than other speakers in the enclosure.

11. The system of claim 1, where the equalization filter coefficients are determined based on the echo compensation filter coefficients by solving a linear equation system with a recursive method.

12. The system of claim 1, further comprising a noise reduction filter configured to reduce noise of at least one of the acoustic input signal and the equalized acoustic input signal.

13. The system of claim 1, where the microphone signal received by the echo compensation filter is received from a microphone installed in a vehicle.

14. A method for enhancing the quality of a first acoustic input signal, comprising:

generating a speaker signal based on a second acoustic input signal by a speaker;

detecting the speaker signal;

generating a microphone signal based on the detected speaker signal;

adapting filter coefficients of an echo compensation filter to echo compensate the microphone signal;

providing a pre-determined reference frequency response approximately representative of the echo compensation filter and an equalization filter, where the filter coefficients of the echo compensation filter are determined based on the pre-determined reference frequency response; and

equalizing the first acoustic input signal with an equalization filter comprising equalization filter coefficients, where the equalization filter coefficients are determined based on the filter coefficients of the echo compensation filter.

15. The method of claim 14, further comprising:

pre-filtering the second acoustic input signal using of a pre-filter that models the transfer function of a microphone to generate a pre-filtered signal, where the filter coefficients of the echo compensation filter are adapted based on the pre-filtered signal.

16. The method of claim 15, where the microphone is a directional microphone located in an enclosure and where the pre-filter models the transfer function of the directional microphone in a direction of a speaker that is located closer to the directional microphone than other speakers located in the enclosure.

17. The method of claim 14, where equalizing comprises solving the linear algebraic equation system:

18. The method of claim 17, where the linear algebraic equation system is solved using a recursive method.

19. A product comprising:

a tangible computer readable medium; and

programmable instructions stored on the computer readable medium that cause a processor in an equalization system to;

generate a speaker signal based on a first acoustic input signal;

detect the speaker signal;

generate a microphone signal based on the detected speaker signal;

adapt filter coefficients of an echo compensation filter to echo compensate the microphone signal; and

equalize a second acoustic input signal with an equalization filter comprising equalization filter coefficients, where the equalization filter coefficients are determined based one the filter coefficients of the echo compensation filter

wherein a reference filter is provided having reference filter coefficients that represent a predetermined reference frequency response of the system including the echo compensation filter and the equalization filter, where the echo compensation filter coefficients are determined based on the reference filter coefficients.

20. The product of claim 19, where the programmable instructions stored on the computer readable medium cause the processor to:

pre-filter the first acoustic input signal using a pre-filter that models the transfer

function of a microphone; and

generate a pre-filtered signal, where the filter coefficients of the echo compensation filter are adapted based on the pre-filtered signal.

21. The product of claim 19, where the pre-determined reference frequency is modeled by multiple reference filter coefficients of a reference filter.

22. The product of claim 19, where the number of equalization filter coefficients is less than the number of filter coefficients of the echo compensation filter.

23. The product of claim 19, where the programmable instructions stored on the computer readable medium cause the processor to generate a speaker signal based on the equalized second acoustic input signal.

24. The product of claim 19, where echo compensation filter comprises a predictive pre-filter.

25. The product of claim 24, where the predictive pre-filter is a linear prediction coding filter.

26. The product of claim 19, where the computer readable medium is implemented in a vehicle to provide hands-free communication between a passenger of the vehicle and a remote party.