An Algorithm for Phase Manipulation in a Speech Signal

While human auditory system is predominantly sensitive to the amplitude spectrum of an incoming sound, a number of sound perception studies have shown that the phase spectrum is also perceptually relevant. In case of speech, its relevance can be established through experiments with speech vocoding or parametric speech synthesis, where particular ways of manipulating the phase of voiced excitation (i.e. setting it to zero or random values) can be shown to affect voice quality. In such experiments the phase should be manipulated with as little distortion of the amplitude spectrum as possible, lest the degradation in voice quality perceived through listening tests, caused by the distortion of amplitude spectrum, be incorrectly attributed to the influence of phase. The paper presents an algorithm for phase manipulation of a speech signal, based on inverse filtering, which introduces negligible distortion into the amplitude spectrum, and demonstrates its accuracy on a number of examples.