Suppression of phasiness for time-scale modifications of speech signals based on a shape invariance property

Time-scale modifications of speech signals, based on frequency-domain techniques, are hampered by two important artifacts which are "phasiness" and "transient smearing". They correspond to the destruction of the shape of the original signal, i.e. the de-synchronization between the phases of the frequency components. This paper describes an algorithm that preserves the shape invariance of speech signals in the context of a phase vocoder. Phases are corrected at the onset of each voiced region. Modified signals, even for large expansion factors, are of high quality and free from transient smearing or phasiness. A demonstration is proposed in the web page: http://www.loria.fr/-jdm/PhaseVocoder/index.html