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Evaluation of a Multiresolution Model of Musical Rhythm Expectancy on Expressive Performances

Leigh M. Smith

A computational multi-resolution model of musical rhythm expectation has been recently proposed based on cumulative evidence of rhythmic time-frequency ridges (Smith & Honing 2008a). This model was shown to demonstrate the emergence of musical meter from a bottom-up data processing model, thus clarifying the role of top-down expectation. Such a multiresolution time-frequency model of rhythm has also been previously demonstrated to track musical rubato well, with both synthesised (Smith & Honing 2008b) and performed audio examples (Coath et. al 2009). The model is evaluated for it's capability to generate accurate expectation from human musical performances. The musical performances consist of 63 monophonic rhythms from MIDI keyboard performances, and 50 audio recordings of popular music. The model generates expectations as forward predictions of times of future notes, a confidence weighting of the expectation, and a precision region. Evaluation consisted of generating successive expectations from an expanding fragment of the rhythm. In the case of the monophonic MIDI rhythms, these expectations were then scored by comparison against the onset times of notes actually then performed. The evaluation is repeated across each rhythm. In the case of the audio recording data, where beat annotations exist, but individual note onsets are not annotated, forward expectation is measured against the beat period. Scores were computed using information retrieval measures of precision, recall and F-score (van Rijsbergen 1979) for each performance. Preliminary results show mean PRF scores of (0.297, 0.370, 0.326) for the MIDI performances, indicating performance well above chance (0.177, 0.219, 0.195), but well below perfection. A model of expectation of musical rhythm has been shown to be computable. This can be used as a measure of rhythmic complexity, by measuring the degree of contradiction to expectation. As such, a rhythmic complexity measure is then applicable in models of rhythmic similarity used in music information retrieval applications.

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