An efficient detuning detection method for the tabla

Tabla, the musical drum, can produce a large number of musical syllables or bols. To produce a good musical performance, the tabla membrane has to be symmetrically tuned to the right pitch. Tabla players sense the extent of such symmetry in the membrane tension by playing the /t̪a:/ bols at eight different locations along the circumference of the tabla. This is a tedious process. Our findings show that a single strike of a /ɽ/ bol can be a good indicator of the presence of asymmetry in membrane tension. Using two stereoscopically arranged high-speed cameras, and an audio data acquisition system, we have investigated /t̪a:/, /ɽ/, and /t̪ʊn/ bols in the context of tuning a tabla. When the membrane was asymmetrically tuned, the frequency spectrum of /ɽ/ bol showed two close peaks corresponding to the second harmonic, and its out-of-plane deflection pattern revealed rotation in mode ψ11 that features one nodal diameter, and one nodal circle corresponding to the rim of the tabla. We noted that such frequency splitting was present even in tablas which had slight asymmetry in the membrane tension. We propose sensing such a frequency-splitting phenomenon to implement an efficient detuning detector for the tabla.