Relative contribution to speech intelligibility of different envelope modulation rates within the speech dynamic range.
The contribution of envelope cues at different rates to intelligibility in a competing-speech task was measured as a function of the short-term envelope level. The target and background mixture was processed using tone vocoders. Envelope signals for each vocoder channel were simultaneously extracted with two low-pass filters, the cutoff frequency of one filter (L) being two octaves below that of the other (H). The envelope from the H filter was used at the peaks and that from the L filter at valleys, or vice versa. This was achieved by cross-fading between the two envelope signals based on a "switching threshold" that was parametrically varied relative to the long-term RMS level of the channel signal. When the cutoff frequencies of the H and L filters were 50 and 12.5 Hz, changes in speech intelligibility occurred mainly when the switching threshold was between -18 and +10 dB. The range was slightly narrower when the cutoff frequencies of the H and L filters were 200 and 50 Hz. Intensity-importance functions for higher-rate envelope modulations suggested that levels ranging from 20 dB below to about 10 dB above the channel RMS level were important, with maximum importance for levels around -5 dB.
Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, England. mas19@cam.ac.uk
Michael A
MA
Stone
Christian
C
Füllgrabe
Brian C J
BC
Moore
D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D001299:Audiometry; D001306:Auditory Pathways / Q000502:physiology*; D001309:Auditory Threshold; D003463:Cues; D005260:Female; D006801:Humans; D008297:Male; D010470:Perceptual Masking; D013018:Sound Spectrography; D013061:Speech Acoustics; D013065:Speech Intelligibility; D013997:Time Factors; D055815:Young Adult