L. Liu J. L. He G. Palm
Dept. Neuroinformation, Univ. of Ulm, 7900 Ulm, Germany
It is well known that under certain conditions, a signal is completely specified either by its Fourier transform phase or amplitude. An iterative technique similar to that used by Hayes et al. [IEEE Trans. Acoust., Speech, Signal Process. ASSP-28, 672--680 (1980)] was applied to the global Fourier transform phases or amplitudes of natural VCV (vowel--stop consonant--vowel) utterances and the perception of stop consonants was experimentally studied. Under a variety of conditions, the consonant identification performance in the phase-only stimuli improved from about 66% to more than 90% after the iterations. The influence of the initial amplitude guess on the quality of the reconstructed signals was also investigated. The retrieval of stop consonant information from phase for various window lengths and various phase noise levels were analyzed with regard to vowel contexts, stop manner, and place of articulation. In contrast to the case of signal reconstruction from its phase, the stimulus reconstructed from the amplitude was found not of much value in representing the original VCV signal. Little improvement on consonant perception could be made after the iterations if a flat or a random phase was taken as the initial guess. However, with an appropriate choice of the initial guess, which contains one bit of the original phase information, stimuli with near-perfect consonant identification performance were reconstructed.