Temporal-envelope constancy of speech in rooms and the perceptual weighting of frequency bands

Abstract

Three experiments measured constancy in speech perception, using natural-speech messages or noise-band vocoder versions of them. The eight vocoder-bands had equally log-spaced center-frequencies and the shapes of corresponding "auditory" filters. Consequently, the bands had the temporal envelopes that arise in these auditory filters when the speech is played. The "sir" or "stir" test-words were distinguished by degrees of amplitude modulation, and played in the context; "next you'll get _ to click on." Listeners identified test-words appropriately, even in the vocoder conditions where the speech had a "noise-like" quality. Constancy was assessed by comparing the identification of test-words with low or high levels of room reflections across conditions where the context had either a low or a high level of reflections. Constancy was obtained with both the natural and the vocoded speech, indicating that the effect arises through temporal-envelope processing. Two further experiments assessed perceptual weighting of the different bands, both in the test word and in the context. The resulting weighting functions both increase monotonically with frequency, following the spectral characteristics of the test-word's [s]. It is suggested that these two weighting functions are similar because they both come about through the perceptual grouping of the test-word's bands.

Enhancement of speech intelligibility in reverberant rooms: Role of amplitude envelope and temporal fine structure

“…They are also consistent with the results of Watkins et al (2011), and demonstrate that the enhancement generalizes to highly variable sentence materials. Taken together, these results may be indicative of mechanisms that compensate for the distortions to the amplitude ENV caused by room reverberation.…”

“…The enhancement is not specific to certain syllable continua (Watkins et al, 2011) but generalizes to highly variable speech sentences that are more representative of that encountered in everyday communication situations. In addition, the enhancement process appears to be very rapid-on the order of seconds-and does not show any long-term improvement.…”

“…There is further evidence that the adaptation processes may depend primarily on the ENV portions of the speech signal, since Watkins et al (2011) have demonstrated similar reverberation adaptation effects for both normal speech sounds and noise vocoded speech, which removes TFS cues but preserves ENV. Because the Watkins et al (2011) study was conducted using phonetically-limited speech materials (syllable continuum from "sir" to "stir"), it is of interest to determine whether this effect generalizes to more natural and phonetically diverse speech materials.…”

Amplitude modulation detection by human listeners in reverberant sound fields: Effects of prior listening exposure

“…Such enhancement is consistent with recent neural data that demonstrate the presence of reverberation-resistant coding of AM in the response properties of single neurons in the inferior colliculus (Delgutte et al, 2012;Kuwada et al, 2012). Because other studies have demonstrated that speech understanding in reverberant soundfields may be modified (Watkins, 2005) or improved (Brandewie and Zahorik, 2010;Srinivasan and Zahorik, 2013) with prior listening exposure to reverberation, and that this effect appears to most strongly influence the processing of the amplitude envelope of the speech signal (Watkins et al, 2011), it is important to determine whether AM sensitivity could be similarly affected by prior listening exposure to reverberation. This is the goal of the present study.…”

Prior listening exposure to a reverberant room improves open-set intelligibility of high-variability sentences

“…The results suggest that when the auditory system is given prior exposure to a reverberant room, it can compensate for the degrading effects of reverberation. This effect appears to depend critically on the amplitude characteristics of the speech waveform's temporal envelope (Watkins et al, 2011), although the effect has also been demonstrated for non-speech sounds (Watkins and Makin, 2007).…”