Adaptive feedback cancellation based on inserted and/or intrinsic characteristics and matched retrieval

• US 8,442,251 B2
• Filed: 04/01/2010
• Issued: 05/14/2013
• Est. Priority Date: 04/02/2009
• Status: Active Grant

• Current Assignee: Oticon A/S (William Demant Fonden)
• Original Assignee: Oticon A/S (William Demant Fonden)
• Inventors: Jensen, Jesper, Elmedyb, Thomas Bo
• Primary Examiner(s): Ni, Suhan
• Application Number:
  US12/681,265
• Publication Number:
  US 20110150257A1
• Time in Patent Office: 1,139 Days
• Field of Search: 381/312, 381317-318, 381/93, 381/94.1, 381/94.9, 381 7111- 12
• US Class Current: 381/318
• CPC Class Codes: H04R 25/453 electronically
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

An audio processing system processing an input sound to an output sound includes: an input transducer for converting input sound to an electric input signal and defining an input side; an output transducer for converting a processed electric output signal to an output sound and defining an output side; a forward path defined between the input transducer and the output transducer; a signal processing unit for processing an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal, and an electric feedback loop from the output side to the input side, having a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and a enhancement unit for estimating noise-like signal components in the electric signal of the forward path and providing a noise signal estimate output.

Claims

1. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal; and

an electric feedback loop from the output side to the input side comprising;

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path, the characteristics of the electric signal including at least one of modulation index, periodicity, correlation time, and noise-like parts of the electric signal, and providing an estimated characteristics output, wherein

the feedback path estimation unit is adapted to use the estimated characteristics output in the estimation of the acoustic feedback transfer function.

2. An audio processing system according to claim 1 wherein said feedback path estimation unit comprises an adaptive filter comprising a variable filter part and an algorithm part for updating filter coefficients of the variable filter part, the algorithm part being adapted to base the update at least partly on said estimated characteristics output from the enhancement unit.

3. An audio processing system according to claim 1, wherein the enhancement unit is adapted for retrieving intrinsic noise-like signal components in the electric signal of the forward path.

4. An audio processing system according to claim 3, wherein the correlation time N₁ of the noise signal estimate output from the enhancement unit obeys N₁≦

dG, where dG is the delay of the forward path.

5. An audio processing system according to claim 1 comprising a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function.

6. An audio processing system according to claim 5 wherein the probe signal generator is adapted to provide a probe signal based on masked added noise.

7. An audio processing system according to claim 5 wherein the probe signal generator is adapted to provide a probe signal based on perceptual noise substitution, PNS.

8. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal; and

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the enhancement unit is configured to retrieve intrinsic noise-like signal components in the electric signal of the forward path, and

the enhancement unit comprises an adaptive filter C(z,n) of the form

9. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the probe signal generator is configured to provide that the probe signal has predefined characteristics, and

the enhancement unit is configured to provide a noise signal estimate output based on said characteristics.

10. An audio processing system

for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the probe signal generator is adapted to provide that the probe signal has a correlation time N₀ which is smaller than or equal to the sum of the forward path and feedback path delays.

11. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the algorithm part of the feedback path estimation unit comprises a step length control block for controlling the step length of the algorithm in a given frequency region, and

the step length control block receives a control input from the probe signal generator.

12. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the probe signal generator is configured to provide a probe signal based on masked added noise,

the probe signal generator comprises an adaptive filter for filtering a white noise input sequence w, the output of the variable part M of the adaptive filter forming the masked probe signal, and the variable part M of the adaptive filter being updated based on a signal from the forward path by an algorithm part comprising a model of the human auditory system.

13. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function,

wherein the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function, wherein

the enhancement unit is configured to base the noise signal estimate output on an adaptive filter configured for filtering a feedback corrected input signal on the input side of the forward path to provide a noise signal estimate output comprising noise-like signal components said feedback corrected input signal.

14. An audio processing system according to claim 13 wherein the adaptive filter is a linear, finite impulse response (FIR) type filter with a time varying long-term prediction, LTP, filter characteristic of the specific form

15. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output; and

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function, wherein

the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function,

the enhancement unit is adapted to provide a noise signal estimate output based on binaural prediction filtering,

an adaptive noise retrieval filter E is adapted for filtering a signal y_c from another microphone, and

the adaptive noise retrieval filter E has a time varying filter characteristic described by the difference equation

16. An audio processing system according to claim 15, wherein

the other microphone is a microphone of a contra-lateral listening device, or an external sensor.

17. An audio processing system according to claim 15, wherein

the other microphone is a microphone of a communication device or of an audio selection device.

18. An audio processing system for processing an input sound to an output sound, the audio processing system comprising:

an input transducer for converting an input sound to an electric input signal and defining an input side;

an output transducer for converting a processed electric output signal to an output sound and defining an output side;

a forward path being defined between the input transducer and the output transducer, and comprising a signal processing unit (SPU) configured to process an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal;

an electric feedback loop from the output side to the input side, including

a feedback path estimation unit for estimating an acoustic feedback transfer function from the output transducer to the input transducer, and

an enhancement unit for extracting characteristics of an electric signal of the forward path and providing an estimated characteristics output;

a probe signal generator for generating a probe signal contributing to the estimation of the feedback transfer function; and

a master enhancement unit on the input side and a slave enhancement unit on the output side, each enhancement unit being electrically connected to the feedback estimation unit, wherein

the slave enhancement unit is adapted to provide the same transfer function as the master enhancement unit, and

the feedback path estimation unit is configured to use the estimated characteristics output in the estimation of the acoustic feedback transfer function.

19. A method of estimating a feedback transfer function in an audio processing system including a feedback estimation system for estimating acoustic feedback, a forward path between an input transducer and an output transducer, and a signal processing unit (SPU) adapted for processing an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal, and an electric feedback loop from the output side to the input side including a feedback path estimation unit for estimating the feedback transfer function from the output transducer to the input transducer, the method comprising:

extracting characteristics of the electric signal of the forward path, said characteristics including at least one of a modulation index, periodicity, correlation time, and noise-like parts of said electric signal;

providing an estimated characteristics output; and

adapting the feedback path estimation unit based on the estimated characteristics output in the estimation of the feedback transfer function.

20. A tangible non-transitory computer-readable medium storing instructions, wherein the instructions when executed on a data processor of an audio processing system including a feedback estimation system for estimating acoustic feedback, a forward path between an input transducer and an output transducer, and a signal processing unit (SPU) adapted for processing an SPU-input signal originating from the electric input signal and to provide a processed SPU-output signal, and an electric feedback loop from the output side to the input side including a feedback path estimation unit for estimating the feedback transfer function from the output transducer to the input transducer, cause the audio processing system to perform a method comprising:

extracting characteristics of the electric signal of the forward path, said characteristics including at least one of a modulation index, periodicity, correlation time, and noise-like parts of said electric signal;

providing an estimated characteristics output; and

adapting the feedback path estimation unit based on the estimated characteristics output in the estimation of the feedback transfer function.