Modulation and Periodic Properties of Temporal Envelope

Abstract

Temporal envelopes are representatives of frequency-dependent signatures of sequences that exhibit the temporal dynamics of signals. This chapter formulates the modulation index, which characterizes the spectral magnitudes of the envelope frequencies normalized. Speech intelligibility is estimated by the modulation index of the narrow-band envelopes. An intriguing question is whether the magnitude or phase spectrum is dominant in synthesizing intelligible speech. Interestingly, it depends on the frame-length. Thus the phase is dominant when the frame length is very long or extremely short. A time-reversed speech sample is used as a good example demonstrating the phase effect on intelligibility. The envelopes also provide estimates of the fundamental period of a periodic sequence. This chapter introduces the period estimation of a periodic scheme when the fundamental of a signal is missing.