The coding group has chosen to focus its researches on the development of
hybrid coders and, more particularly, on Code Excited Linear Prediction
coders (originally proposed by Atal and Schroeder). These coders produce low-rate
coded speech comparable to that of medium-rate waveform coders.
These coders determine the system parameters by linear prediction and the excitation sequence
is determined by close-loop or analysis-by-synthesis optimization. The optimization
process chooses an excitation sequence which minimizes a measure of the weighted difference between
the input speech and the coded speech. The weighting function is chosen such that the coder is "optimized" for the human ear.
The synthesis block consists of a short-term synthesis filter
which represents the formant structure of speech, a long-term synthesis filter which represents the pitch structure
of the speech. A perceptual filter is used to shape the error such that the quantization noise is masked by
the speech signal. A excitation generator forms or selects an excitation sequence such that the weighted
Mean Squared Error (MSE) is minimized. The CELP coder produces low-rate coded speech comparable to that
of medium-rate waveform coders.
Last updated December 17, 1999, send comments to firstname.lastname@example.org