Pitch Combinations and Grouping

Auditory scene analysis is a seminal theory of auditory perception, which was first developed by Albert Bregman in the 1970s, with antecedents in Gestalt theory and, before that, Aristotle. The theory focuses on the manner in which the human auditory system organizes sound into perceptually meaningful units. The theory posits that the grouping of elements with regard to sound sources precedes the perception of source attributes (Bregman, 1990). The word source as it is used here refers to the object producing the sound—for example, a musical instrument. Hence, a listener must establish what aspects of the scene belong together before establishing the pitch of any one source. The auditory scene in music, which tends to be highly organized in comparison to natural auditory scenes, is often complex. One of the factors contributing to this complexity is the presence of multiple sources playing simultaneously (e.g., separate voices in a chorale). When multiple pitches occur simultaneously, some will fuse together (tonal fusion) while others will be heard as separated (tonal fission). The result of this ongoing auditory scene analysis will influence our experience of melodic, harmonic, and rhythmic structure.

Several factors have been identified as influencing tonal fusion in simultaneous pitch combinations. The most important among these include harmonicity, onset asynchrony, comodulation, and to a lesser extent, spatial positioning. Although these are all separate processes, which can be put into conflict with each other, the general explanatory principle that unites them is that sounds and sound components are more likely to fuse together when they appear to belong to a single source. I will refer to this generalized principle as the single source hypothesis and will discuss it at various points in the chapter.