Room reverberation and constancy in sparse noise-vocoded speech.
Anthony J. Watkins, Andrew P. Raimond, Simon J. Makin · The Journal of the Acoustical Society of America · 2011
Speech played several metres from the listener in a room is usually heard to have much the same phonetic content as it does when played nearby, although the different amounts of reverberation at these distances make the temporal envelopes of these signals very different. To study this “constancy” effect, listeners heard natural-speech messages and noise-excited vocoder versions of them. The vocoder used eight auditory-filter shaped noise-bands, each with the temporal envelope arising in that filter when the speech message is played. The center frequencies of the equally log-spaced bands ranged from 250 Hz to 4.24 kHz. An 11-step “sir-to-stir” continuum was formed by amplitude modulation and each step was played in the context, “next you’ll get … to click on.” Listeners identified test words appropriately, even in the eight-band conditions where the speech had a robotic quality. Constancy was assessed by comparing the influence of reverberation on the test word across conditions where the context had either the same level of reverberation (i.e., from the same, far distance), or where it had a much lower level (i.e., from nearby). Constancy effects were obtained with both the natural- and the eight-band speech, with the higher-frequency bands having more importance.