Detection and representation of rhythm and tempo I: The rhythmogram

Abstract

In the paper an algorithm is presented for the computation of a primitive representation of rhythmic structure [N. P. Todd, J. New Mus. Res. 23, 25–70 (1994)]. The algorithm consists of the following stages: (1) cochlear filtering, by means of an ear model based on the gammatone filter-bank [M. Cooke, Modeling Auditory Processing and Organisation (Cambridge University Press, Cambridge, MA, 1992)]; (2) modulation filtering, by means of a Gaussian low-pass modulation filter-bank; (3) peak detection and integration of the output of the modulation filter-bank. When the peak outputs of the modulation filters are plotted in a time-constant/time diagram they form a representation, referred to as a rhythmogram, which resembles a more conventional tree diagram of rhythmic structure. A single acoustic event gives rise to a single branch in the representation so that integration along a branch yields a single number corresponding to the perceptual prominence or stress of the event. The integration mechanism can be thought of as an acoustic sensory memory process and accounts for a number of important phenomena in rhythm perception, including persistence, partial backward masking, interval produced accents and grouping by temporal proximity and accent. This representation may form the input to higher level learning and recognition mechanisms.