Echo canceller for non-linear circuits
First Claim
1. In an audio circuit comprising a microphone and a loudspeaker, said microphone detecting a speech signal from a near-end user, said loudspeaker receiving a far-end speech signal and generating a corresponding echo signal that is also detected by said microphone, a method of cancelling the echo signal comprising the steps of:
- providing at least one other microphone in said audio circuit for detecting said echo signal, said at least one other microphone also detecting said near-end speech signal;
estimating a plurality of acoustic transfer functions in a plurality of adaptive filters each having a plurality of coefficients, at least one of said adaptive filters using the far-end speech signal as a reference signal for adjusting its coefficients;
filtering the outputs of one or more of said microphones using the coefficients of one or more of said adaptive filters; and
combining the filtered and any unfiltered microphone outputs so as to substantially cancel said echo signal while substantially preserving said near-end speech signal.
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Abstract
A system and a method for echo suppression which use two or more microphones for beamforming of an echo signal corresponding to an incoming speech signal that is output by a loudspeaker. The outputs of the microphones are appropriately filtered and then linearly combined to cancel the echo signal, even if the incoming speech signal has been non-linearly distorted. Also, the microphones may be selectively positioned or pointed to allow the linear cancellation of ambient noise.
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Citations
68 Claims
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1. In an audio circuit comprising a microphone and a loudspeaker, said microphone detecting a speech signal from a near-end user, said loudspeaker receiving a far-end speech signal and generating a corresponding echo signal that is also detected by said microphone, a method of cancelling the echo signal comprising the steps of:
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providing at least one other microphone in said audio circuit for detecting said echo signal, said at least one other microphone also detecting said near-end speech signal; estimating a plurality of acoustic transfer functions in a plurality of adaptive filters each having a plurality of coefficients, at least one of said adaptive filters using the far-end speech signal as a reference signal for adjusting its coefficients; filtering the outputs of one or more of said microphones using the coefficients of one or more of said adaptive filters; and combining the filtered and any unfiltered microphone outputs so as to substantially cancel said echo signal while substantially preserving said near-end speech signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A circuit for cancelling an echo signal from an audio source comprising:
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a first microphone for detecting said echo signal along a first path defined by a first acoustic transfer function H1 ; a second microphone for detecting said echo signal along a second path defined by a second acoustic transfer function H2 ; a first adaptive filter for estimating H1 ; a second adaptive filter for estimating H2 ; a first fixed filter for filtering the output of said first microphone using the estimate of H2 ; a second fixed filter for filtering the output of said second microphone using the estimate of H1 ; and means for subtracting the output of said second fixed filter from the output of said first fixed filter so as to cancel said echo signal. - View Dependent Claims (31, 32, 33, 34)
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35. A circuit for cancelling an echo signal from an audio source comprising:
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a first microphone for detecting said echo signal along a first path defined by a first acoustic transfer function H1 ; a second microphone for detecting said echo signal along a second path defined by a second acoustic transfer function H2 ; a first adaptive filter for estimating H1 ; a second adaptive filter for estimating H2 ; a fixed filter for filtering the output of said second microphone using an acoustic transfer function H1 /H2 based on the estimates of H1 and H2 ; and means for subtracting the output of said fixed filter from the output of said first microphone so as to cancel said echo signal. - View Dependent Claims (36, 37, 38, 39)
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40. A circuit for cancelling an echo signal from an audio source comprising:
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a first microphone for detecting said echo signal along a first path defined by a first acoustic transfer function H1 ; a second microphone for detecting said echo signal along a second path defined by a second acoustic transfer function H2 ; a first adaptive filter for estimating 1/H1 and for filtering the output of said first microphone; a second adaptive filter for estimating 1/H2 and for filtering the output of said second microphone; and means for subtracting the output of said second adaptive filter from the output of said first adaptive filter so as to cancel said echo signal. - View Dependent Claims (41, 42, 43)
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44. A circuit for cancelling an echo signal from an audio source comprising:
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a first microphone for detecting said echo signal along a first path defined by a first acoustic transfer function H1 ; a second microphone for detecting said echo signal along a second path defined by a second acoustic transfer function H2 ; a first adaptive filter for estimating H1 ; a second adaptive filter for estimating 1/H2 and for filtering the output of said second microphone; a fixed filter for filtering the output of said second adaptive filter using the estimate of H1 ; and means for subtracting the output of said fixed filter from the output of said first microphone so as to cancel said echo signal. - View Dependent Claims (45, 46, 47, 48)
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49. A circuit for cancelling an echo signal from an audio source comprising:
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a first microphone for detecting said echo signal along a first path defined by a first acoustic transfer function H1 ; a second microphone for detecting said echo signal along a second path defined by a second acoustic transfer function H2 ; a first adaptive filter for estimating H1 ; a second adaptive filter for estimating H1 /H2 and for filtering the output of said second microphone; and means for subtracting the output of said second adaptive filter from the output of said first microphone so as to cancel said echo signal. - View Dependent Claims (50, 51, 52)
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53. In a speech communications system including a loudspeaker which generates an echo signal from an incoming signal, an echo cancellation circuit comprising:
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a plurality of microphones for detecting said echo signal from said loudspeaker; means for estimating a plurality of acoustic transfer functions using the incoming signal as a reference signal; means for filtering one or more of the outputs of said microphones using one or more of the estimated acoustic transfer functions; and means for combining the filtered outputs of the microphones so as to cancel said echo signal. - View Dependent Claims (54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68)
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Specification