Eight-channel digital speech synthesizer based on LPC techniques

An automatic vocal response system for the Italian language has been implemented at CSELT, consisting of a hardware speech synthesizer controlled by a programmed device (mini or micro computer). The synthesizer exploits a speech production model composed of a 10th order digital lattice filter and two excitation generators for voiced and unvoiced sounds. The hardware includes also a module, which controls the updating and transfer of the parameters, and an output module which provides the analog speech signal. The synthesizer configuration is modular and expandible up to 8 channels. For each channel, the minicomputer supplies the synthesizer with the start-stop command plus 13 parameters: 10 filter coefficients, a gain factor, the pitch period and voiced-unvoiced information and the updating interval. For each channel, every 125 µs, 20 multiplications, 9 addition and 10 subtractions are executed. The filter and the source generator are time-shared among the 8 channels. The complete digital equipment is implemented by TTL-LS integrated circuits.