A new mixed excitation LPC vocoder

The authors introduce a novel synthesizer structure for an LPC (linear predictive coding) vocoder which increases the clarity and naturalness of the output speech. This synthesizer enhances the usual excitations of either periodic pulses or white noise by allowing pulse/noise mixtures and aperiodic pulses, and thus can generate a wider range of possible speech signals. The control algorithms for this new model replace the traditional binary voicing decision with more robust periodicity, peakiness, and power level detectors, without a significant increase in bit rate. As a result, the vocoder produces synthetic speech which is free of the usual LPC synthesis artifacts, even at bit rates below 2400 bps