Variable bit-rate methods for low-delay speech coders

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Abstract

Abstract: Several efficient Variable-Bit-Rate MR) methods suitable for low-delay Delayed-Decision Tree-Code (DDTC) and CELP speech coders are presented in this paper. These methods are based on modifying the existing codebook(s) by means of block or lattice codes. To achieve a reduced rate operation of the DDTC coder a novel technique based on a parity code is developed and up to 2 dB SNR improvement uver conventional methods is demonstrated. For extended rate operation of the LD-CELP coder an approach based on a lattice code is used. The modified or additional lattice codebook has a geometrical (algebraic) structure, allowing the search procedure to be performed efficiently and with minimal additional memory. Simulation results of these VBR methods for a 16 kbit/s DDTC coder and for the 16 kbit/s LD-CELP coder proposed for the CCITT recommendation (G.728) are presented.

Original languageEnglish
Pages (from-to)183-192
Number of pages10
JournalSpeech Communication
Volume12
Issue number2
DOIs
StatePublished - Jun 1993

Keywords

  • CELP
  • LD-CELP
  • VBR
  • Variable-bit-rate
  • lattice codebook
  • parity code
  • speech coding

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