Method and apparatus for estimating the level of acoustic feedback between a loudspeaker and microphone
First Claim
1. In an echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:
- an adjustable filter for receiving a loudspeaker signal and generating in response thereto an echo estimation signal,means for subtracting said echo estimation signal from the microphone signal to produce an echo corrected microphone signal, andmeans for adjusting transfer characteristics of said filter, during periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, to reduce said echo corrected microphone signal, the improvement comprising;
means for estimating an energy transfer ratio representative of the ratio of the energy of the microphone signal to the energy of the loudspeaker signal, andmeans for comparing the microphone signal to the energy transfer ratio multiplied by the loudspeaker signal to identify said periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone.
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Abstract
An improved echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system. The device includes an adjustable filter for receiving a loudspeaker signal and generating in response thereto an echo estimation signal. The device subtracts the echo estimation signal from the microphone signal to produce an echo corrected microphone signal. During periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, the device adjusts transfer characteristics of the filter to reduce the echo corrected microphone signal. The improvement includes estimating from the adjusted transfer characteristics an energy transfer ratio representative of the ratio of the energy of the microphone signal to the energy of the loudspeaker signal. The device compares the microphone signal to the energy transfer ratio multiplied by the loudspeaker signal to identify periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone.
157 Citations
18 Claims
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1. In an echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:
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an adjustable filter for receiving a loudspeaker signal and generating in response thereto an echo estimation signal, means for subtracting said echo estimation signal from the microphone signal to produce an echo corrected microphone signal, and means for adjusting transfer characteristics of said filter, during periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, to reduce said echo corrected microphone signal, the improvement comprising; means for estimating an energy transfer ratio representative of the ratio of the energy of the microphone signal to the energy of the loudspeaker signal, and means for comparing the microphone signal to the energy transfer ratio multiplied by the loudspeaker signal to identify said periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone. - View Dependent Claims (2, 3, 4, 5)
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6. In an echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:
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an adjustable filter for receiving a loudspeaker signal and generating in response thereto an echo estimation signal, means for subtracting said echo estimation signal form the microphone signal to produce an echo corrected microphone signal, means for adjusting transfer characteristics of said filter, during periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, to reduce the echo corrected microphone signal, and a clipper for attenuating said echo corrected microphone signal during selected periods of time, the improvement comprising; means for calculating a reverberation estimate representative of reverberation of the loudspeaker signal, means for comparing the echo corrected microphone signal to the reverberation estimate, and means for enabling said signal clipper to attenuate during periods of time when said echo corrected microphone signal is less than said reverberation estimate. - View Dependent Claims (7, 8, 9)
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10. In a method for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:
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applying a loudspeaker signal to an adjustable filter to generate an echo estimation signal, subtracting said echo estimation signal from a microphone signal to produce an echo corrected microphone signal, adjusting transfer characteristics of said filter, during periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, to reduce said echo corrected microphone signal, the improvement comprising the steps of; estimating an energy transfer ratio representative of the ratio of the energy of the microphone signal to the energy of the loudspeaker signal, comparing the microphone signal to the energy transfer ratio multiplied by said loudspeaker signal to identify said periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone. - View Dependent Claims (11, 12, 13, 14)
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15. In a method for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising the steps of:
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applying a loudspeaker signal to an input of an adjustable filter to generate an echo estimation signal, subtracting said echo estimation signal from the microphone signal to produce an echo corrected microphone signal, adjusting transfer characteristics of said filter, during periods of time when the microphone signal is substantially derived from acoustic feedback between the loudspeaker and the microphone, to reduce said echo corrected microphone signal, attenuating said echo corrected microphone signal during selected periods of time, the improvement comprising the steps of; calculating from said adjusted transfer characteristics a reverberation estimate representative of room'"'"'s reverberation of said loudspeaker signal, comparing the echo corrected microphone signal to the reverberation estimate, and identifying, based on said comparisons said periods of time when said echo corrected microphone signal is less than said reverberation estimate. - View Dependent Claims (16, 17, 18)
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Specification