A multi-mode variable rate CELP coder based on frame classification

The authors present a modular CELP (code-excited linear prediction) coder which can switch bit-rates in response to local speech characteristics (source-controlled mode) or external network conditions (network-controlled mode). The coder is capable of operating at several bit-rates and is optimized for 16 kb/s, 8 kb/s, and 4 kb/s. A 925-b/s configuration is included for silent frames. The authors present the results of informal MOS tests which show that the variable-rate system running at an average rate of 8 kb/s achieves subjective speech quality close to that of the 16-kb/s fixed-rate system (a difference of less than 0.1 on the MOS scale).<<ETX>>

[1]  S. A. Mahmoud,et al.  Tree searched multi-stage vector quantization of LPC parameters for 4 kb/s speech coding , 1992, [Proceedings] ICASSP-92: 1992 IEEE International Conference on Acoustics, Speech, and Signal Processing.

[2]  Allen Gersho,et al.  Real-time vector APC speech coding at 4800 bps with adaptive postfiltering , 1987, ICASSP '87. IEEE International Conference on Acoustics, Speech, and Signal Processing.

[3]  Allen Gersho,et al.  An overview of variable rate speech coding for cellular networks , 1992, 1992 IEEE International Conference on Selected Topics in Wireless Communications.

[4]  I. A. Gerson,et al.  Vector sum excited linear prediction (VSELP) speech coding at 8 kbps , 1990, International Conference on Acoustics, Speech, and Signal Processing.

[5]  William R. Gardner,et al.  QCELP: A Variable Rate Speech Coder for CDMA Digital Cellular , 1993 .

[6]  Allen Gersho,et al.  Improved phonetically-segmented vector excitation coding at 3.4 kb/s , 1992, [Proceedings] ICASSP-92: 1992 IEEE International Conference on Acoustics, Speech, and Signal Processing.

[7]  Manfred R. Schroeder,et al.  Code-excited linear prediction(CELP): High-quality speech at very low bit rates , 1985, ICASSP '85. IEEE International Conference on Acoustics, Speech, and Signal Processing.