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Noise eliminating apparatus and speech recognition apparatus using the same

  • US 5,212,764 A
  • Filed: 04/24/1992
  • Issued: 05/18/1993
  • Est. Priority Date: 04/19/1989
  • Status: Expired due to Term
First Claim
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1. A noise eliminating apparatus coupled to a recognition device for recognizing an input speech signal, said noise eliminating apparatus comprising:

  • a) first amplifier means for amplifying a first acoustic signal and for generating a first amplified acoustic signal, said first acoustic signal including the input speech signal to be recognized;

    b) first feature extracting means, coupled to said first amplifier means, for generating a feature quantity of said first amplified acoustic signal for each of n channels, said feature quantity including a power spectrum;

    c) second amplifier means for amplifying a second acoustic signal and for generating a second amplified acoustic signal;

    d) second feature extracting means, coupled to said second amplifier means, for generating a feature quantity of said second amplified acoustic signal for each of said n channels, said feature quantity including a power spectrum;

    e) speech section detecting means, coupled to said first and second feature extracting means, for detecting a speech section of said first acoustic signal for each of said n channels by using the feature quantity of said first amplified acoustic signal and the feature quantity of said second amplified acoustic signal; and

    f) a noise eliminating unit, coupled to said first and second feature extracting means and said speech section detecting means, said noise eliminating unit including;

    1) first means for generating a first noise eliminating variable k(f) and a second noise eliminating variable d(f) on the basis of a feature quantity Xn(f) extracted by said first feature extracting means and a feature quantity Nn(f) extracted by said second feature extracting means when said first acoustic signal does not include the input speech signal and thus said speech section detecting means does not detect the speech section; and

    2) second means for generating a feature quantity of said input speech signal which is to be supplied to the recognition device on the basis of a feature quantity Xs(f) extracted by said first feature extracting means and a feature quantity Ns(f) extracted by said second feature quantity extracting means when said first acoustic signal includes the input speech signal and thus said speech section detecting means detects the speech section;

    wherein said first noise eliminating variable k(f) and said second noise eliminating variable d(f) are defined as a function satisfying the following;

    (i) the first noise eliminating variable k(f) approaches zero and the second noise eliminating variable d(f) approaches the feature quantity Xn(f) as the feature quantity Xn(f) becomes smaller than a predetermined value; and

    (ii) the first noise eliminating variable k(f) approaches Xn(f)/Nn(f) and the second noise eliminating variable d(f) approaches zero as the feature quantity Xn(f) becomes greater than the predetermined value.

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