Analysis of /t̪a:/ and /t̪ʊn/ bols of the tabla from a musical standpoint

Abstract

Tabla, the Indian harmonic musical drum, produces several distinct sounds or bols, which are rhythmically arranged into different taals (beat-cycles) to work as a syllabic musical poem. Prior research on tabla has primarily focused on the tabla membrane’s vibrational attributes and how such attributes get influenced by the tabla’s structure. Thus, there is a need to study the tabla from a musical standpoint and understand the linkages between its vibrations and the acoustical attributes of its musical bols. We fill this gap by analyzing the two most important bols; /t̪a:/ and /t̪ʊn/. Towards this, we studied bols produced by ten experienced tabla players using four different tablas tuned to different notes spanning an octave. To extract the tabla’s vibro-acoustical features, we employed two stereoscopically arranged high-speed cameras and an audio data acquisition system in tandem. Our work brings out several salient features of these bols including correspondences between the method of producing a bol and its acoustical attributes, the presence of nearly degenerate modes, the phenomenon of frequency splitting due to asymmetric loading of tabla membrane and the consequential beats, the musical importance of some inharmonicities, and psychoacoustic implications of certain frequencies missing in a bol’s spectrum. Such understanding will not only help us understand the musical acoustics of the tabla better, but also guide us towards an improved tabla design.