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Speech selective automatic gain control

  • US 5,146,504 A
  • Filed: 12/07/1990
  • Issued: 09/08/1992
  • Est. Priority Date: 12/07/1990
  • Status: Expired due to Term
First Claim
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1. A communication device including an automatic gain control circuit comprising:

  • an analog-to-digital converter, coupled to a source of analog audio signals, for producing a digital input signal representing the analog audio signal;

    first delay means, coupled to the analog-to-digital converter for delaying the digital input signal provided by the analog-to-digital converter;

    power detector means, coupled to the first delay means, for detecting the power level of the digital input signal, and for producing a linear power signal representing the power level of the digital signal;

    a linear-to-logarithmic converter, coupled to the power detector means, for converting the linear power signal into a logarithmic power signal;

    speech smoothing means, coupled to the linear-to-logarithmic converter, for smoothing the logarithmic power signal to provide a smoothed logarithmic power signal;

    a first summer for substracting the smoothed logarithmic power signal from a reference signal to provide a logarithmic error signal representing a logarithmic gain signal;

    gain smoothing means, coupled to the summer, for smoothing the logarithmic gain signal to provide a smoothed logarithmic gain signal;

    a logarithmic-to-linear converter, coupled to the gain smoothing means, for converting the smoothed logarithmic gain signal to a smoothed linear gain signal;

    a multiplier for multiplying the smoothed linear gain signal with the digital input signal to provide an amplified digital input signal; and

    a speech recognizer, coupled to the analog-to-digital converter, for determining whether the digital input signal represents recognizable speech, and for enabling the detected speech smoothing means and the gain smoothing means, when speech is detected in the input signal.

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