System for suppressing acoustic echoes and interferences in multi-channel audio systems

• US 20020054685A1
• Filed: 09/17/2001
• Published: 05/09/2002
• Est. Priority Date: 11/09/2000
• Status: Abandoned Application

• Current Assignee: Creative Technology Ltd.
• Original Assignee: Creative Technology Ltd.
• Inventors: Dolson, Mark, Avendano, Carlos, LaRoche, Jean
• Application Number:
  US09/956,476
• Publication Number:
  US 20020054685A1
• Time in Patent Office: Days
• US Class Current: 381/66
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A method for obtaining a clean speech signal in a communication system having a transducer for receiving a clean speech signal from a user and having a pair of loudspeakers for providing an output signal to the user. The output signal contains loudspeaker signals which interfere with the clean speech signal, the loudspeaker signals traveling through acoustic paths to reach the transducer. The transducer receives an input signal containing the loudspeaker signals and the clean speech signal. The method includes a number of steps, namely, performing a short time Fourier transform (STFT) on the input signal to obtain at least one frequency component, performing a short time Fourier transform (STFT) on the loudspeaker signals to obtain frequency components, summing the frequency components to obtain an interference sum, and subtracting the interference sum from the at least one frequency component to obtain the clean speech signal for translation into a time domain.

Claims

1. A method for suppressing an interference signal from a microphone output signal to produce a clean speech signal, the interference signal being first and second loudspeaker signals modified by first and second acoustic paths through which the loudspeaker signals reach a microphone, the interference signal combining with the clean speech signal to form the microphone output signal, the method comprising:

determining an acoustic response for each of the first and second acoustic paths in a frequency domain;

determining an estimate of the interference signal in a frequency domain using the acoustic response for each of the first and second acoustic paths;

suppressing the estimate of interference signal from the microphone output signal to obtain the clean speech signal in the frequency domain; and

translating the clean speech signal into time domain.

2. The method of claim 1 further comprising estimating a delay for synchronizing the microphone output signal with the first and second loudspeaker signals.

3. The method of claim 1 wherein the clean speech signal contains pauses of nonspeech intervals, and the step of determining the acoustic response is performed during a pause.

4. The method of claim 1 further comprising decorrelating the first and second loudspeaker signals prior to the step of determining an acoustic response.

5. The method of claim 1 wherein the step of determining an estimate of the interference signal comprises decomposing each of the first and second loudspeaker signals into first and second frequency signals, respectively.

6. The method of claim 5 further comprising modifying the first frequency signal by the acoustic response of the first acoustic path to obtain a first interference estimate.

7. The method of claim 6 further comprising modifying the second frequency signal by the acoustic response of the second acoustic path to obtain a second interference estimate.

8. The method of claim 7 further comprising combining the first interference estimate and the second interference estimate to obtain a magnitude of the interference signal.

9. The method of claim 8 wherein the step of suppressing the interference signal comprises subtracting the magnitude of the interference signal from a magnitude of the microphone output signal.

10. The method of claim 1 wherein the step of determining an acoustic response comprises generating a sequence of white noise signals for output through the first and second loudspeakers.

22. The method of claim 1 wherein the step of determining the acoustic response comprises generating a sequence of white noise signals for output through the first and second loudspeakers.

23. The method of claim 4, wherein the step of decorrelation is carried out by any one or more of amplitude modulation, random panning and adding additive noise.

11. In a communication system having a transducer for receiving a clean speech signal from a user, and having first and second loudspeakers for providing an output signal to the user, the output signal containing first and second loudspeaker signals which interfere with the clean speech signal traveling through first and second acoustic paths to reach the transducer, the transducer receiving an input signal containing the first and second loudspeaker signals and the clean speech signal, a method of obtaining the clean speech signal, the method comprising:

performing a short-time Fourier transform (STFT) on the input signal to obtain at least one frequency component;

performing a short-time Fourier transform (STFT) on the first and second loudspeaker signals to obtain first and second frequency components, respectively;

summing the first and second frequency components to obtain an interference sum; and

subtracting the interference sum from the at least one frequency component to obtain the clean speech signal for translation into a time domain.

12. The system of claim 11 further comprising modifying the first frequency component with a transfer function of the first acoustic path, prior to the step of summing the first and second frequency components.

13. The system of claim 12 further comprising modifying the second frequency component with a transfer function of the second acoustic path, prior to the step of summing the first and second frequency components.

15. The system of claim 14 further comprising a filter module modifying the first frequency sub-band signal using an acoustic response of the first acoustic path, and for modifying the second frequency sub-band signal using an acoustic response of the second acoustic path.

16. The system of claim 14 further comprising an adder for summing the first and second frequency sub-band signals to obtain a magnitude of an interfering signal.

17. The method of claim 14 further comprising an adaptation module estimating an acoustic response of the first acoustic path, and for estimating an acoustic response of the second acoustic path.

19. The method of claim 18 further comprising estimating a delay for synchronizing the microphone output signal with the first and second loudspeaker signals.

20. The method of claim 18 wherein the step of determining a sum of magnitudes for each of the first and second frequency domain signals further comprises obtaining an acoustic response of first and second acoustic paths.

21. The method of claim 18 further comprising modifying the first echo signal by the acoustic response of the first acoustic path to obtain a first interference estimate for the first loudspeaker signal, and modifying the second frequency signal by the acoustic response of the second acoustic path to obtain a second interference estimate for the second loudspeaker signal.

14. In a communication system having a local microphone for transmitting signals to a remote user through a communication channel, and first and second local loudspeakers for receiving signals from the remote user via the communication channel, the microphone receiving a microphone output signal comprising a clean speech signal from a local user and an interference signal from the first and second loudspeakers, a system for suppressing the interference signal, the system comprising:

a first transform module performing a short-time Fourier transform (STFT) on the first loudspeaker signal to obtain a first frequency sub-band signal;

a second transform module performing a short-time Fourier transform (STFT) on the second loudspeaker signal to obtain a second frequency sub-band signal;

a third transform module performing a short-time Fourier transform (STFT) on the microphone output signal to obtain a third frequency sub-band signal;

a subtractor module subtracting the first and second frequency sub-band signals from the third frequency sub-band signal to obtain a clean speech signal; and

an inverse short-time Fourier transform (ISTFT) module translating the clean speech signal into time domain.

18. An acoustic echo suppression method comprising:

receiving an input signal containing first and second acoustic echo signals and a clean speech signal;

transforming the first and second acoustic echo signals into first and second frequency domain signals;

determining a sum of magnitudes for each of the first and second frequency domain signals;

transforming the input signal into a third frequency domain signal;

determining a sum for the magnitude of the first frequency domain signal and the second frequency domain signal;

determining a magnitude of the third frequency domain signal; and

canceling the first and second echo signals by generating a difference signal between the sum of the magnitudes for each of the first and second frequency domain signals and the magnitude of the third frequency domain signal, the difference signal being transformed into a time domain signal to obtain the clean speech signal.