Control of spectral dynamics in concatenative speech synthesis

Current speech synthesis methods based on the concatenation of waveform units can produce highly intelligible speech capturing the identity of a particular speaker. However, the quality of concatenated speech often suffers from discontinuities between the acoustic units, due to contextual differences and variations in speaking style across the database. In this paper, we present methods to spectrally modify speech units in a concatenative synthesizer to correspond more closely to the acoustic transitions observed in natural speech. First, a technique called "unit fusion" is proposed to reduce spectral mismatch between units. In addition to concatenation units, a second, independent tier of units is selected that defines the desired spectral dynamics at concatenation points. Both unit tiers are "fused" to obtain natural transitions throughout the synthesized utterance. The unit fusion method is further extended to control the perceived degree of articulation of concatenated units. A signal processing technique based on sinusoidal modeling is also presented that enables high-quality resynthesis of units with a modified spectral shape.