Adaptive noise cancelling microphone system

• US 20040047464A1
• Filed: 09/11/2002
• Published: 03/11/2004
• Est. Priority Date: 09/11/2002
• Status: Active Grant

• Current Assignee: Nanyang Technology University
• Original Assignee: Nanyang Technology University
• Inventors: Yu, Zhuliang, Ser, Wee
• Granted Patent: US 6,917,688 B2
• Time in Patent Office: Days
• US Class Current: 379/392.01
• CPC Class Codes: G10K 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: G10K 2210/1082 Microphones, e.g. systems using "virtual" microphones
• CPC Class Codes: G10K 2210/3018 Correlators, e.g. convolvers or coherence calculators
• CPC Class Codes: H04M 9/08 Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic

Abstract

An adaptive noise canceling microphone system for extracting a desired signal, in particular a desired speech signal, comprising two microphones being arranged at a predefined distance from each other; a signal forming system (SFS) being adapted to receive a first and second input signals resulting from sounds received by the two microphones wherein an acoustical signal component in the first input signal is determined, wherein an acoustical signal component in the second input signal is determined, wherein the acoustical signal component in the first input signal is enhanced to generate a speech enhanced signal, and wherein the acoustical signal component in the second input signal is suppressed to generate a speech nulled signal; an adaptive noise cancellation filtering circuit being adapted to receive the speech enhanced signal and the speech nulled signal, wherein the noise in the speech enhanced signal is cancelled using the speech nulled signal as reference, thereby generating an output filtered signal representing the desired signal.

Claims

1. An adaptive noise canceling microphone system for extracting a desired signal, in particular a desired speech signal, comprising:

two microphones being arranged at a predefined distance from each other;

a signal forming system (SFS) being adapted to receive a first and second input signal resulting from sounds received by the two microphones,

wherein an acoustical signal component in the first input signal is determined,

wherein an acoustical signal component in the second input signal is determined,

wherein the acoustical signal component in the first input signal is enhanced to generate a speech enhanced signal, and

wherein the acoustical signal component in the second input signal is suppressed to generate a speech nulled signal;

an adaptive noise cancellation filtering circuit being adapted to receive the speech enhanced signal and the speech nulled signal, wherein the noise in the speech enhanced signal is cancelled using the speech nulled signal as reference, thereby generating an output filtered signal representing the desired signal.

2. The adaptive noise canceling microphone system according to claim 1, further comprising a post processing filtering circuit for reducing noise from the output filtered signal, wherein the post processing filtering circuit is adapted to receive the output filtered signal, using the speech enhanced signal and the speech nulled signal as reference, and to generate a digital result signal representing the output filtered signal with noise reduced.

3. The adaptive noise canceling microphone system according to claims 1 or 2, further comprising an adaptive noise cancellation microphone (ANCM) controller for receiving the speech enhanced signal, the speech nulled signal and the output filtered signal, the adaptive noise cancellation microphone (ANCM) controller being adapted to generate an adaptive noise cancellation filter (ANCF) control signal and an SFS control signal for updating coefficients of at least one filter of the SFS and adaptive noise cancellation filtering circuit, respectively, using the received speech enhanced signal, the speech nulled signal and the output filtered signal.

4. The adaptive noise canceling microphone system according to claim 3, wherein the adaptive noise cancellation microphone controller is adapted to generate a post processing filter control signal for updating the coefficients of the at least one filter of the post processing filtering circuit.

5. The adaptive noise canceling microphone system according to claim 3, wherein the SFS comprises

a first FIR filter and a second FIR filter for receiving the first input signal, wherein the first FIR filter and the second FIR filter are adapted to determine the acoustical signal component in the first input signal, and to generate a first FIR filtered signal and a second FIR filtered signal, respectively, representing the acoustical signal component in the first input signal;

a first adder for adding the first FIR filtered signal to the second input signal, thereby generating the speech enhanced signal;

a second adder for subtracting the second FIR filtered signal from the second input signal, thereby generating the speech nulled signal;

6. The adaptive noise canceling microphone system according to claim 5, wherein the SFS further comprises a Least Means Squared (LMS) algorithm block, wherein the LMS algorithm blocked is adapted to receive the first input signal, the SFS control signal and the speech nulled signal, and to update the coefficients of the first and/or second FIR filters.

7. The adaptive noise canceling microphone system according to claim 5, wherein the SFS further comprises a first Read Only Memory (ROM) and a second Read Only Memory (ROM), wherein information representing the coefficients of the first FIR filter and the second FIR filter are stored in the first ROM and the second ROM, and the stored information in the ROMs are used as coefficients for the first FIR filter and the second FIR filter, respectively.

8. The adaptive noise canceling microphone system according to claim 3, wherein the adaptive noise cancellation filtering circuit comprises

an adaptive filter being adapted to receive speech nulled signal, and to generate a filtered signal representing noise in the first and second input signal,

wherein the ANCF control signal is used to update the coefficients of the adaptive filter, and

wherein an error signal from the adder is used as feedback information to the adaptive filer,

an adder for subtracting the filtered signal from the speech enhanced signal, and generating the error signal.

9. The adaptive noise cancellation microphone system according to claim 8, further comprising a delay circuit arranged between the speech enhanced signal and the adder, wherein the delay circuit is adapted to receive and delay the speech enhanced signal, and to generate a delayed signal to the adder.

10. The adaptive noise cancellation microphone system according to claim 8, further comprising

an additional adder arranged between the speech nulled signal and the adaptive filter for subtracting an additional filtered signal of the additional adaptive filter from the speech nulled signal, and generating an additional error signal to the adaptive filter;

and

an additional adaptive filter being adapted to receive the error signal, and to generate the additional filtered signal representing an estimated component of the desired signal in the error signal,

wherein the ANCF control signal is used to update the coefficients of the additional adaptive filter, and

wherein the additional error signal is used as a feedback information to the additional adaptive filter.

11. The adaptive noise cancellation microphone system according to claim 9, further comprising

an additional adder arranged between the speech nulled signal and the adaptive filter for subtracting an additional filtered signal of the additional adaptive filter from the speech nulled signal, and generating an additional error signal to the adaptive filter;

and

an additional adaptive filter being adapted to receive the error signal, and to generate the additional filtered signal representing an estimated component of the desired signal in the error signal,

wherein the ANCF control signal is used to update the coefficients of the additional adaptive filter, and

wherein the additional error signal is used as a feedback information to the additional adaptive filter.

12. The adaptive noise cancellation microphone system according to claim 2, wherein the post processing filtering circuit comprises

a FIR filter being adapted to receive the output filtered signal and to generate the digital result signal,

a coefficient calculation block being adapted to receive the speech enhanced signal, the speech nulled signal and the output filtered signal, and to generate a coefficient signal representing the coefficients of the FIR filter;

13. The adaptive noise cancellation microphone system according to claim 12, wherein the coefficient calculation block is further adapted to receive a post processing control signal, wherein the post processing control signal is also used to generate the coefficient signal representing the coefficients of the FIR filter.

14. The adaptive noise cancellation microphone system according to claim 3, wherein the adaptive noise cancellation controller comprises

a power estimator unit being adapted to receive each of the speech enhanced signal, the speech nulled signal and the output filtered signal, and to generate a corresponding power signal to be received by a silence detector unit and a signal detector unit;

the silence detector unit for detecting whether an acoustical signal is present in the speech enhanced signal input, the speech nulled signal and the output filtered signal, and being adapted to generate a first output signal which indicates whether the acoustical signal is present;

a signal detector unit for detecting whether a desired signal is present in the speech enhanced signal, the speech nulled signal and the output filtered signal, and being adapted to generate a second output signal which indicates whether the desired signal is present;

an adaptive noise cancellation filter controller unit being adapted to receive the first output signal and the second output signal to determine the characteristic of the first input signal and the second input signal, and to generate the ANCF control signal which represents an updated coefficient parameter for updating the coefficients of the at least one filter of the adaptive noise cancellation filtering circuit; and

an SFS controller unit being adapted to receive the first output signal and the second output signal to determine the characteristic of the first input signal and the second input signal, and to generate the SFS control signal which represents an updated coefficient parameter for updating the coefficients of the at least one filter of the SFS.

15. The adaptive noise cancellation microphone system according to claim 4, wherein the adaptive noise cancellation controller comprises

a power estimator unit being adapted to receive each of the speech enhanced signal, the speech nulled signal and the output filtered signal, and to generate a corresponding power signal to be received by a silence detector unit and a signal detector unit;

the silence detector unit for detecting whether an acoustical signal is present in the speech enhanced signal input, the speech nulled signal and the output filtered signal, and being adapted to generate a first output signal which indicates whether the acoustical signal is present;

a signal detector unit for detecting whether a desired signal is present in the speech enhanced signal, the speech nulled signal and the output filtered signal, and being adapted to generate a second output signal which indicates whether the desired signal is present;

an adaptive noise cancellation filter controller unit being adapted to receive the first output signal and the second output signal to determine the characteristic of the first input signal and the second input signal, and to generate the ANCF control signal which represents an updated coefficient parameter for updating the coefficients of the at least one filter of the adaptive noise cancellation filtering circuit; and

an SFS controller unit being adapted to receive the first output signal and the second output signal to determine the characteristic of the first input signal and the second input signal, and to generate the SFS control signal which represents an updated coefficient parameter for updating the coefficients of the at least one filter of the SFS.

16. The adaptive noise cancellation microphone system according to claim 15, wherein the adaptive noise cancellation controller further comprises a post processing filter controller unit, wherein the post processing filter controller unit is adapted to receive the first output signal and the second output signal to determine the characteristic of the first input signal and the second input signal, and to generate a post processing control signal which represents an updated coefficient parameter for updating the coefficients of at least one filter of the post processing filtering circuit.

17. The adaptive noise canceling microphone system according to claim 1, further comprises

a first amplifier and a second amplifier for receiving and amplifying signals resulting from the sounds received by the two microphones;

a first low pass filter and a second low pass filter for receiving and filtering the amplified signals from the first amplifier and the second amplifer, thereby generating analog amplified and filtered signals;

a first Analog-to-Digital converter and a second Analog-to-Digital converter for receiving and converting the analog amplified and filtered signals to digital signals, thereby generating the first input signal and the second input signal.

18. The adaptive noise cancellation microphone system according to claim 2, further comprising a Digital-to-Analog converter for converting the digital result signal to an analog signal, thereby generating an output result signal.