CS-ACELP at 8 kbit/s

The coder is based on the Code-Exited Linear-Prediction (CELP) coding model. It operates on a digital input signal specified with 16 bit (PCM linear) at 8 kHz sampling rate. The decoder converts the received signal after decoding back to an analogue signal. For every 10 ms frame, the speech signal is analysed to extract the parameters of the CELP model (linear-prediction filter coefficients, adaptive- and fixed-codebook indices and gains). These parameters are encoded and transmitted. At the decoder, these parameters are used to retrieve the excitation signal and synthesis filter parameters. The speech is reconstructed by filtering the excitation signal through the short-term synthesis filter. This filter is based on a 10th order Linear Prediction (LP) filter. The long-term, or pitch synthesis filter is implemented using the so-called adaptive-codebook approach. After computing the reconstructed speech, it is further enhanced by a postfilter.