Method and apparatus for low-delay CELP speech coding and decoding
AssigneeAT&T Bell Laboratories
InventorJuin-Hwey Chen
Life of this patent
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Abstract
A low-bitrate (typically 8 kbit/s or less), low-delay digital coder and decoder based on Code Excited Linear Prediction for speech and similar signals features backward adaptive adjustment for codebook gain and short-term synthesis filter parameters and forward adaptive adjustment of long-term (pitch) synthesis filter parameters. A highly efficient, low delay pitch parameter derivation and quantization permits overall delay which is a fraction of prior coding delays for equivalent speech quality at low bitrates.
Claims36
In a method of coding F-millisecond frames of samples of an input signal sampled at a rate of R kilobits per second with a coding delay of D milliseconds comprising the steps of
- for each of a plurality of codebook vectors having respective index signals
- adjusting said vectors by a gain factor to generate a
- gain-adjusted vector,
- applying said gain-adjusted vector to the cascade of
- a long-term filter reflecting long-term characteristics of said input signals and
- a short-term filter reflecting short-term characteristics of said input signals,
- thereby to generate a synthesized candidate signal comparing each of said candidate signals with said frame of sampled input signals to determine the candidate signal best approximating said frame of sampled input signals, making available the index corresponding to the candidate signal best approximating said frame of sampled input signals for subsequent decoding of said frame,
- deriving filter parameters for said long term filter,
- making available said filter parameters for subsequent decoding of said frame,
- The Improvement Comprising the further step of
- deriving filter parameters for said short-term filter by backward adaptation.
Dependencies are inferred from the claim text.