Appropriate windowing for group delay analysis and roots of z-transform of speech signals

This study discusses the difficulties of phase spectrum analysis of speech signals and shows that appropriate windowing is very crucial for obtaining reliable phase spectra. The main difficulties of phase based analysis stem from the domination of spiky effects of roots (zeros) of the signal z-transform close to the unit circle. We show how this problem is linked to windowing by discussing zero-patterns for speech signals. Once windowing is performed properly, group delay functions are much less noisy and reveal clearly formant information.