We have designed a system that increases the intelligibility of speech signals in noise by manipulating the parameters of a harmonic speech model. The system performs the transformation in two steps: in the first step, it modifies the spectral slope, which is closely related to the vocal effort; in the second step, it amplifies low-energy parts of the signal using dynamic range compression techniques. Objective and subjective measures involving speech-shaped noise confirm the effectiveness of these simple methods. As the harmonic model has been used in previous works to implement the waveform generation module of high-quality statistical synthesizers, the system presented here can provide the synthesis engine with a higher degree of control on the intelligibility of the resulting artificial speech.

Index Terms: speech intelligibility in noise, harmonic model, speech synthesis, spectral tilt, dynamic range compression