Voice source model for continuous control of pitch period

The voiced speech waveform may be synthesized by exciting an LPC vocal tract filter with a pulse waveform patterned after naturally occurring glottal airflow pulses. Such a pulse waveform may be generated by computing samples of a piecewise polynomial curve at equally spaced time intervals. In this type of synthesis, the pitch period is commonly restricted to an integer multiple of the sample interval. A method is presented for removing this restriction, permitting both pulse duration and pitch period to be varied over continuous time. Aliasing distortion is prevented by computing the sample values of pulses that have been low-pass filtered in continuous time prior to sampling. Applications of this technique include modeling glottal pulses by least-squares fit to inverse filter waveforms, the synthesis of calibration waveforms for evaluating measures of speech waveform jitter, the perceptual evaluation of low levels of waveform jitter, and the synthesis of the singing voice.