Evaluating the Benefit of Recorded Early Reflections From a *Classroom for Speech Intelligibility
Larsen, Jeffery B.
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https://hdl.handle.net/2142/85212
Description
Title
Evaluating the Benefit of Recorded Early Reflections From a *Classroom for Speech Intelligibility
Author(s)
Larsen, Jeffery B.
Issue Date
2005
Doctoral Committee Chair(s)
Lansing, Charissa R.
Department of Study
Speech and Hearing Science
Discipline
Speech and Hearing Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Acoustics
Language
eng
Abstract
Recent standards for classrooms acoustics recommend achieving low levels of reverberation to provide suitable conditions for speech communication (ANSI, 2002; ASHA, 1995). Another viewpoint recommends optimizing classroom acoustics to emphasize early reflections and reduce later arriving reflections (Boothroyd, 2004; Bradley, Sato, & Picard, 2003). The idea of emphasizing early reflections is based in the useful-to-detrimental ratio (UDR) model of speech intelligibility in rooms (Lochner & Burger, 1964). The UDR model predicts that listeners integrate energy from early reflections to improve the signal-to-noise (SNR) of the direct speech signal. However, both early and more recent studies of early reflections and speech intelligibility have used simulated reflections that may not accurately represent the effects of real early reflections on the speech intelligibility of listeners. Is speech intelligibility performance enhanced by the presence of real early reflections in noisy classroom environments? The effect of actual early reflections on speech intelligibility was evaluated by recording a binaural impulse response (BRIR) with a K.E.M.A.R. in a college classroom. From the BRIR, five listening conditions were created with varying amounts of early reflections. Young-adult listeners with normal hearing participated in a fixed SNR word intelligibility task and a variable SNR task to test if speech intelligibility was improved in competing noise when recorded early reflections were present as compared to direct speech alone. Mean speech intelligibility performance gains or SNR benefits were not observed with recorded early reflections. When simulated early reflections were included, improved speech understanding was observed for simulated reflections but for with real reflections. Spectral, temporal, and phonemic analyses were performed to investigate acoustic differences in recorded and simulated reflections. Spectral distortions in the recorded reflections may have rendered them less useful to listeners than non-distorted, simulated reflections. The findings of the present investigation suggest caution when generalizing the results of speech intelligibility experiments using simulated reflections to real classroom listening. The results support the ANSI 12.60 standard and also provide a framework for investigating both the integration characteristics of human listeners for broadband signals in reverberation and the effect of real reverberant environments on the speech intelligibility of listeners in controlled settings.
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