Harmonic postprocessing of speech synthesised by stochastic coders

High quality speech coding at medium-to-low bit rates is presently one of the major goals in speech research. Stochastic coding represents an important step towards this objective. Yet, the quality of synthetic speech is still not always good enough. A subjectively important part of the distortion may arise from imperfect reproduction of voiced regions, where the harmonic structure is not was well marked in the synthetic signal as it is in the original speech signal. Postprocessing of synthetic signals using harmonic modelling arises as a natural solution to reduce this distortion. The disadvantages of this method in terms of additional delay, complexity and dependency on high precision pitch detectors can be well counter-balanced by the higher quality of resynthesised speech signals in voiced regions.