To achieve high-quality singing synthesis, spectral modeling and physical modeling have been used in the past. However, spectral models are known to be articulation difficult and expressivity limited. On the other hand, it is not straightforward to adjust physical model parameters to reproduce a specific recording. In this thesis, a high-quality singing synthesizer is proposed with its associated analysis procedure to retrieve the model parameters automatically from the desired voices. Since 95% of singing is voiced sound, the focus of this research is to improve naturalness of the vowel tone quality. In addition, an intuitive parametric model is also developed to control the vocal textures of the synthetic voices ranging from “pressed", to "normal", to "breathy" phonation.
To trade off between complexity of the model and the corresponding analysis procedure, a source-filter type synthesis model is proposed. Based on a simplified human voice production system, the source-filter synthesis model describes human voices as the output of the vocal tract filter excited by a glottal excitation. The vocal tract is modeled as an all-pole filter since only non-nasal voiced sound is focused. To accommodate variations of vocal textures, the glottal excitation model consists of two elements: the derivative glottal wave and the aspiration noise. The derivative glottal wave is modeled by the transformed Liljencrants-Fant (LF) model. Moreover, the aspiration noise is represented as pitch-synchronous, amplitude-modulated Gaussian noise.
The major contribution of this thesis is the
development of an analysis procedure that estimates the parameters of the
proposed synthesis model to mimic the desired voices. First, a source-filter
de-convolution algorithm via the convex optimization technique is proposed to
estimate the vocal tract filter from sound recordings. Second, the inverse
filtered glottal excitation is decomposed into a smoothed derivative glottal
wave and a noise residual component via Wavelet Packet Analysis. Proper
parameterizations of the glottal excitation can then be found. By analyzing
baritone recordings, a parametric model is constructed for controlling vocal
textures in synthesized singing.
Synthetic sounds were generated by exciting the estimated vocal tract filter by the estimated KLGLOTT88 derivative glottal wave obtained during the source-filter de-convolution step of the analysis procedure.
Synthetic sounds were generated by exciting the estimated vocal tract filter by the fitted LF derivative glottal wave.
These sound examples illustrate the importance of noise source for breathy voice. The derivative glottal wave source is only secondary compared to the noise source. Without the presence of the noise source, the output vowel sounds nasal but not breathy.
Last modified: 6/20/02 11:17AM Pst 2002