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Voiced, unvoiced or noise modes in a CELP vocoder

  • US 5,734,789 A
  • Filed: 04/18/1994
  • Issued: 03/31/1998
  • Est. Priority Date: 06/01/1992
  • Status: Expired due to Term
First Claim
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1. A method of processing a signal having a speech component, the signal being organized as a plurality of frames, the method comprising the steps, performed for each frame, of:

  • measuring a value for at least one speech characteristic of a frame, wherein the speech characteristic is selected from the group consisting of spectral stationarity, pitch stationarity, high-frequency content, and energy;

    comparing the measured value of the selected speech characteristic with at least two thresholds, including a high threshold representing a high value of the selected speech characteristic and a low threshold representing a low value of the selected speech characteristic; and

    setting a first flag if the measured value exceeds the high threshold; and

    setting a second flag if the measured energy value is below the low threshold;

    determining whether the frame lacks a substantial speech component based on the determined flags;

    classifying the frame in a noise mode if the frame lacks a substantial speech component, and in a speech mode otherwise; and

    generating an encoded frame in accordance with a noise mode coding scheme if the frame is classified in the noise mode, and in accordance with a speech coding scheme if the frame is classified in the speech mode.

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