BWV 1002 Allemande melodic fission example

music cognition Music psychology, or the psychology of music, may be regarded as a branch of both psychology and musicology. It aims to explain and understand musical behaviour and experience, including the processes through which music is perceived, created, res ...

, melodic fission (also known as melodic or auditory streaming, or stream segregation), is a phenomenon in which one line of pitches (an auditory stream) is heard as two or more separate melodic lines. This occurs when a

phrase In syntax and grammar, a phrase is a group of words or singular word acting as a grammatical unit. For instance, the English expression "the very happy squirrel" is a noun phrase which contains the adjective phrase "very happy". Phrases can consi ...

contains groups of pitches at two or more distinct registers or with two or more distinct

timbre In music, timbre ( ), also known as tone color or tone quality (from psychoacoustics), is the perceived sound quality of a musical note, sound or tone. Timbre distinguishes different types of sound production, such as choir voices and musica ...

s. The term appears to stem from a 1973 paper by W. J. Dowling. In

music analysis Musical analysis is the study of musical structure in either compositions or performances. According to music theorist Ian Bent, music analysis "is the means of answering directly the question 'How does it work?'". The method employed to answe ...

and, more specifically, in Schenkerian analysis, the phenomenon is often termed compound melody. In psychophysics,

auditory scene analysis In perception and psychophysics, auditory scene analysis (ASA) is a proposed model for the basis of auditory perception. This is understood as the process by which the human auditory system organizes sound into perceptually meaningful elements. T ...

is the process by which the brain separates and organizes sounds into perceptually distinct groups, known as auditory streams. The counterpart to melodic fission is melodic fusion.

Contributing factors

Register

Listeners tend to perceive fast melodic sequences which contain tones from two different registers as two melodic lines. The greater the distance between groups of tones in a melody, the more likely they will be heard as two different and interrupted streams instead of one continuous stream. Studies involving the interleaving of two melodies have found that the closer the melodies are in register, the more difficult it is for listeners to perceptually separate the melodies. Tempo is important, as the threshold for registrar distance between melodic phrases still perceived as one stream increases as the tempo of the melody decreases.

Timbre

The more distinct the timbre of groups of pitches within one stream, the greater the likelihood that listeners will separate them into different streams. Similar to results found with experiments in pitch level, slower tempos increase the chance of perception of timbrally distinct pitches as one continuous stream. Timbral difference may override registral similarity in the perception of segregated streams. Additionally, quick and contrasting attack times in groups of tones lead to fission.

Volume

Differences in volume of groups of pitches can also lead to stream segregation. Logically, the louder the volume of a group of tones, the greater likelihood of melodic fission. In addition, when two streams are perceptually segregated due to differences in volume, the quieter stream is perceived as continuous, but interrupted by the louder stream.

Repetition

Perception of separate streams builds as the melodic sequence is repeated over time, first rapidly, and then at a decreased rate. However, a few factors can impede this process and "reset" fission perception, including silence between presentation of the melody, alteration of signal location (right or left ear) of the melody, and abrupt changes in volume.

References