Synthesis of breathy vowels : some research methods

When vowels are synthesised by means of a source-filter model, a delta-pulse train is often used as a source signal. Although breathiness can to some extent be simulated by using a sophisticated glottal-source model, a more natural simulation of breathiness requires the addition of aspiration noise. When stationary noise is used, however, the noise is to a large extent perceived as coming from a separate sound source which hardly contributes to the breathy timbre of the vowel. This problem can be solved by using noise with a temporal envelope of the same periodicity as the pulse train. In a simple source-filter model, a combination of lowpass-filtered pulses and synchronous highpass-filtered noise bursts of equal energy was used as a source signal. In this way, the noise was no longer perceived as a separate sound, but integrated perceptually with the strictly periodic part of the signal. It will be shown that this integration consists of both a reduction of the loudness of the separate noise stream and a timbre change in the breathy vowel.