Overview of Streaming

Streaming is a term used to describe the way the brain "sorts" the auditory information presented to it by the ear. This assignment uses a carefully designed sequence of notes and timbres to determine the point at which the method used by the brain to sort the information changes.

Each of the four different shapes (and colours) in the diagram above represents a different timbre. In the test, this sequence is repeated seamlessly until the subject ends the test. When the notes are played slowly, for example around 60bpm, the sequence of notes is usually perceived as an ascending scale, with the timbre of each note changing. This is known as note order streaming. When the notes are played rapidly, for example at 600bpm or faster, the sequence is perceived as a descending series of scales, each of the same timbre. This is called timbral streaming. Usually, listeners can pick out any of the four descending scales at will.

At some point between these two extremes, the effect gradually changes from one to the other, and many listeners can around this point deliberately switch from effect to the other. The aim of this assignment is to discover where this point is for several subjects. (Top)

Experiment Design

A computer program was written in order to provide a controllable, accurate note generator. An important part of the program design was the decision to allow the user to adjust the tempo freely, so that the subject was free to listen to both streaming effects before gradually homing in on the convergence of the two effects, and then being able to remain at a particular tempo until certain. To allow even greater control here, a range control was provided so that the tempo could be broadly adjusted and then fine tuned to within 5ms.

Other features in the program design to allow the user to feel as comfortable as possible include a volume adjuster, a very simple visual indication on screen that something is happening, and the use of a timing mechanism that allows the user's input to be reacted to immediately. Additionally, although the value of the rest between each note played is the measurement being taken here, an increased rest or pause value results in a slower musical tempo, and so the opportunity was taken to display the tempo in beats per minute and allow the user to adjust the "speed" rather than the "rest length". (Top)

An annotated overview of the code structure is here, and the raw C code file is here.

Test Results

In accordance with the assignment instructions, the test was carried out on the author and one other subject. The two results were:

The significant difference between the two results backs up the comment made by both subjects that the precise point at which the effect changes is very hard to pinpoint. It is impossible to draw conclusions from such a small sample set, other than to comment that both subject perceived the point at which the streaming effect changed within the expected boundaries, and that more subjects would indicate the accuracy with which this point could be identified. (Top)

This work was carried out in 1999 by Alastair Disley as part of the MSc course in Music Technology at the University of York.