After a review of terminology, this paper presents an hypothesis for the psychoacoustic origins of the perception of spaciousness (assumed to be closely related to or identical to the perception of envelopment) and the apparent source width (ASW). The paper proposes that the apparent source width is broadened by reflected energy arriving during the rise time of musical sound segments (notes), while the perception of envelopment arises from reflected energy which arrives during sound segments or after they end. In addition we hypothesize that the perception of the most musically desirable form of spaciousness depends on the neural process which separates sound into a foreground stream (the sound segments themselves), and a background stream (the reverberation.) Our experiments suggest that the perception of the background stream is completely inhibited for at least 50 ms after the ends of sound segments, and the inhibition decreases to zero over an additional time period of 70 ms to 120 ms. Preliminary experiments find that when there are clear gaps between foreground sound events, the loudness of the background stream is absolute - independent of the loudness of the foreground stream. This view of the psychoacoustic origin of ASW and spaciousness suggests that ASW will not depend on the absolute loudness of the foreground segments, and that when sound segments have short rise times ASW will be narrow, even in a soundfield where the perception of spaciousness (and envelopment) is strong. The proposals also imply that the perception of spaciousness (and envelopment) will depend on 1. the absolute strength of the reverberant field at least 120 to 170 ms after the ends of sound events; 2. the spatial properties of the reverberant field in the same time period; and 3. the proportion of gaps in the musical source material which allows the background stream to be heard. Although there is currently insufficient experimental data to fully support these hypotheses, they make predictions which are both useful and easily tested.
Document Type: Short Communication
Publication date: July 1, 1997
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Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.