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Noise reduction apparatus and method

  • US 6,757,395 B1
  • Filed: 01/12/2000
  • Issued: 06/29/2004
  • Est. Priority Date: 01/12/2000
  • Status: Expired due to Term
First Claim
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1. A method for reducing noise in audio processing applications, the method comprising:

  • separating audio signals through an analysis filter into a plurality of processing bands, wherein each said processing band processes said audio signals within a predetermined frequency band;

    generating a gain function for noise reduction in each said processing band, wherein said gain function comprises a gain scale function providing a predetermined amount of gain as a function of a ratio of a signal envelope to a noise envelope and a maximum attenuation function providing a predetermined maximum attenuation;

    combining the output of each said gain function with the input of each said gain function in a multiplying circuit; and

    combining the outputs of said multiplying circuits in a synthesis filter to produce a stream of processed audio samples, wherein said generating a gain function for noise reduction in each said processing band comprises;

    (1) calculating the magnitude of each of a stream of input samples;

    (2) converting the output of step (1) into the decibel domain;

    (3) estimating the signal envelope of the output of step (2);

    (4) estimating the noise envelope based on the output of step (3);

    (5) generating a decibel domain gain scale function for noise reduction as a function of the outputs of steps (3) and (4);

    (6) generating a decibel domain maximum attenuation function;

    (7) combining the outputs of steps (5) and (6); and

    (8) converting the output of step (7) from the decibel domain to the magnitude domain.

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