×

Outbound noise cancellation for telephonic handset

  • US 5,406,622 A
  • Filed: 09/02/1993
  • Issued: 04/11/1995
  • Est. Priority Date: 09/02/1993
  • Status: Expired due to Term
First Claim
Patent Images

1. In a telephone instrument comprising a transmit microphone and means connecting said instrument to a telephone network, apparatus for reducing entry into said network of acoustic background noise comprising:

  • a reference microphone for picking up noise signals;

    a noise-cancellation circuit comprising a first adaptive filter connected to said transmit microphone for conditioning speech signals and a second adaptive filter for receiving a signal consisting substantially of noise only, for conditioning said noise signals;

    each said filter comprising;

    plural transversal elements arrayed as serial delay lines each having an output tap following each said element, and each said filter further comprising weighting means for modifying the outputs of its respective taps;

    said first adaptive filter comprising means for periodically sampling the output of said transmit microphone and said second adaptive filter comprising means for periodically sampling said noise-only signal;

    said first adaptive filter weighting means being adapted for modifying the outputs of the corresponding output taps in accordance with the most recent transmit microphone samples;

    means for additively combining the outputs of said respective first adaptive filter taps and second adaptive filter taps to produce a respective output for each said filter;

    first summing means for summing the outputs of said reference microphone and said first filter;

    means for connecting the output of said first summing means to the input of said second filter;

    second summing means for summing the outputs of said second filter and of said transmit microphone and for feeding the result to a network;

    first settable threshold means defining the presence of speech and second settable threshold means defining the absence of speech;

    means including said first and said second settable threshold means for generating, when a measure of speech power exceeds said first threshold means, a first signal indicative of the presence of speech at said transmit microphone and for generating, when said measure of speech power falls below said second threshold means, a second signal indicative of the absence of speech at said transmit microphone;

    means, responsive to said first signal, for updating said weighting means of said first adaptive filter while holding said weighting means of said second adaptive filter frozen; and

    means, responsive to said second signal, for updating said weighting means of said second adaptive filter while holding said weighting means of said first adaptive filter frozen.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×