A robust 2400 bps subband LPC vocoder

This paper presents a new voice coder for applications in future low bit rate communication systems. The emphasis has been put on the speech quality, noise robustness and complexity. The coder realizes a multiband+LPC spectral analysis and synthesis of speech. The transmitted information consists of an LPC10 filter, a set of voicing rates, pitch, energies, spectral density of excitation in five subbands, and information about the stationarity of the signal in each half-frame. Depending upon this stationarity, the quantization process is adapted to provide more spectral information (stable speech) or more temporal information (transitory speech). In order to be less sensitive to the surrounding noise, the pitch and voicing rates are first computed in each subband. The final values of these parameters are obtained from the values in the current frame and its neighbours. The excitation signal used at the synthesis side consists of a mixture of isolated pulses, periodic and aperiodic signals of adjustable spectral composition. Tests results are provided.