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Method and apparatus for noise reduction by filtering based on a maximum signal-to-noise ratio and an estimated noise level

  • US 6,032,114 A
  • Filed: 02/12/1996
  • Issued: 02/29/2000
  • Est. Priority Date: 02/17/1995
  • Status: Expired due to Term
First Claim
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1. A method for reducing noise in an input speech signal, the method comprising the steps of:

  • converting the input speech signal into a frequency spectrum;

    determining filter characteristics byobtaining a first value representing a ratio of a signal level of the frequency spectrum to an estimated noise level of a noise spectrum contained in the frequency spectrum from a table containing a plurality of pre-set signal levels of the frequency spectrum of the input speech signal and a plurality of pre-set estimated noise levels of the noise spectrum in order to determine an initial value of the filter characteristics, andobtaining a second value representing a maximum value of a ratio of a frame-based signal level of the frequency spectrum to a frame-based estimated noise level and the frame-based estimated noise level for variably controlling the filter characteristics; and

    reducing noise in the input speech signal by noise filtering using the determined filter characteristics, includingdecreasing the noise filtering when the frame-based signal level is greater than the frame-based estimated noise level, andincreasing the noise filtering when the frame-based signal level is less than the frame-based estimated noise level.

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