Envelope filtering of signals in the modulation frequency domain and evaluation of fluctuation strength

Abstract

Fluctuation strength assessments with predefined envelope variations are commonly performed with synthesized modulated sounds. The intent of the present study is to change gradually the variability of recorded signals’ envelopes for subsequent fluctuation strength evaluations. Manipulation of a signal’s envelope was achieved by implementing a filter in the modulation frequency domain. Making use of an algorithm developed by R. Koch [B. Kollmeier and R. Koch, J. Acoust. Soc. Am. 95, 1593–1602 (1994)], time signals are transformed into (waterfall-like) bandpass-time signals (bandwidth 86 Hz) by calculating the spectra of successive frames. From the time-dependent envelopes of the bandpasses, modulation spectra are computed and filtered. Time signals with changed envelopes are resynthesized from the filtered modulation spectra by reversing the former processing stages. The fluctuation strength of the original and modified time signals was computed and compared with the subjective assessments. The results of this comparison are used to validate an algorithm for fluctuation strength calculations of recorded signals.