Leigh M. Smith

Demonstrations

Foot-tapping with Rubato

This is an example of automatic interpretation of an anapest rhythm undergoing extreme asymmetrical rubato (tempo variation). The foot-tapper plays a hi-hat sound along to a test anapestic rhythm (repeated short-short-long) which is being varied in it's tempo. The tapper has found the underlying repetition rate and selectively chosen to tap on the first beat of the groups of three, respecting (with a slight error) the rubato of the rhythm. This gives a robust means to interpret and synthesize ritards, accelerando, grooves and swing.

Clapping to Auditory Salience Traces

The continuous wavelet transform (CWT) of Morlet and Grossman can also be applied to decompose a rhythm represented by a continous trace of event "salience" derived directly from the audio signal. We use a measure of event salience developed by our EmCAP partners Prof. Sue Denham and Dr. Martin Coath at the University of Plymouth. The CWT decomposes the event salience trace into a hierarchy of periodicities (a multi-resolution representation). These periodicities have a limited duration in time (hence the term "wavelets"). Where those periodicities continue to be reinforced by the occurrance of each onset of the performed rhythm, a limited number of periodicities are continued over time, forming "ridges". The ridges can then be used to identify periods in the rhythm which match listeners sense of beat. These ridges can then be recomposed using the inverse wavelet transform to produce moments in time that match the taps of the beat.

An audio example below demonstrates beat induction of singing. The first MP3 file is the original sung fragment (Thanks are due to the Meertens Institute for supplying the Dutch folk songs from the "Onder de groene linde" collection). The second MP3 file is the same song with the beat induced by the multiresolution representation process mixed in as a hi-hat sound.

Singing Example

Accompanied Singing Example