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Method for detecting and masking bad frames in coded speech signals

  • US 5,255,343 A
  • Filed: 06/26/1992
  • Issued: 10/19/1993
  • Est. Priority Date: 06/26/1992
  • Status: Expired due to Fees
First Claim
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1. A method of improving the detection and masking of bad frames in a coded speech signal resulting from channel transmission errors, said coded speech signal having a first group of bits comprising the most significant bits of said coded speech signal, error detection bits and error correction bits, a second group of bits comprising the second most significant bits and error correction bits and a third group of bits comprising the least significant bits, said method comprising the steps of:

  • de-interleaving said coded signal to obtain a first series of bits comprising said first and second group of bits and a second series of bits comprising said third group of bits;

    convolutionally decoding said first series of bits for recovering said first and second group of bits;

    performing a Cyclic Redundancy Code (CRC) check on recovered bits of said first group;

    if said CRC check is successful, utilizing said third group of bits and said recovered bits of said first group for speech decoding and performing a maximum likelihood check on said second group of bits;

    if said maximum likelihood check is successful, utilizing said recovered bits of said second group for speech decoding; and

    if said maximum likelihood check is unsuccessful, replicating the pitch lag value and sub-frame gain for each sub-frame of said bad frame, from the last sub-frame of the previously accepted frame.

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