Generation of growl-type voice qualities by spectral morphing

In this paper we introduce a morph-based approach for generating voice source aperiodicities frequently associated with strong vocal expressions, especially in singing. In our approach the excitation characteristics of one signal are combined the fundamental frequency and spectral envelope characteristics of another signal. An exemplar sustained sample of the target voice quality is looped and resampled in the time domain in order to generate a continuous signal matching the input voice´s fundamental frequency. This operation preserves most of the sample´s voice quality characteristics at the cost of scaling time and frequency dimensions. While we found the temporal scaling to be acceptable in many contexts, the frequency scaling has to be inverted in order to generate appropriate spectral content for the source excitation´s entire bandwidth. This can be accomplished by the phase-locked vocoder method of modulating harmonic bands in frequency. Finally, the input signal´s harmonic amplitudes and phases are applied to the transformed morph sample, allowing for a simple one-dimensional control of morph amount by linear interpolation with the input signal. The proposed system is evaluated and the results are discussed.