A vowel synthesizer based on F0-modulated formant sinusoids

A vowel synthesizer based on F0-modulated formant sinusoids

Ingo Hertrich & Hermann Ackermann

Department of Neurology, University of Tübingen, Germany


A vowel synthesis algorithm was developed resembling parallel formant synthesizers. However, formants are computed as amplitude- and phase-modulated sinusoids instead of being represented by recursive filters or resonators. The fundamental frequency is imposed on the signal in the following way: Each pitch period starts with a short initial rise of a duration of pi/2 of the first formant frequency; at the end of this ramp phase all formants start as sinusoids at pre-defined phase angles and amplitudes, and successively undergo linear attenuation toward zero amplitude at the end of each pitch period. Adjacent pitch periods, thus, do not influence each other. In principle, the signals produced by this algorithm resemble the output of parallel formant synthesizers (eg., Klatt, D.H., J. Acoust. Soc. Am. 67, 971-995, 1980). However, by incremental sample-by-sample computation of the formants' phase angles, formant frequencies are allowed to continuously change within single pitch periods. This algorithm produces vowels as well as formant transitions signalling stop consonant-vowel syllables such as /ba/, exhibiting a homogeneous, stereotypic voice quality. Because of its additive procedure, this method might allow for the implementation of a variety of further acoustic aspects of the human speaking voice in a well-controlled manner.