| 摘要 |
A teleconferencing system having an echo canceller is configured for use at a large near-end conference location having a loudspeaker for acoustic reproduction of a received far-end telecommunication signal, a plurality of microphones and local acoustic amplification of the signals produced by the microphones. At least one first microphone is located relative to the loudspeaker such that the acoustic delay time between the loudspeaker and the first microphone is less than or equal to the tail length of the echo canceller. At least one second microphone is located relative to the loudspeaker such that the acoustic delay time between the loudspeaker and the second microphone is greater than the tail length of the echo canceller. Signals from the first and second microphones are provided to a mixer and are mixed to provide a send-input signal to the echo canceller. The echo canceller is configured to remove an echo component from the send-input signal, thereby to provide a send-output signal for transmission to a far-end location. A gate is provided between the second microphone and the mixer for selectively interrupting or attenuating the second microphone signal during periods when the near-end acoustic signal substantially consists of far-end speech. The gate may be configured to selectively connect the second microphone with the mixer when the second microphone signal exceeds a predetermined or adaptive threshold based on the amplitude of the far-end telecommunication signal.
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