Abstract:

In this paper we introduce a physical model of the Gyil, an African pentatonic idiophone whose wooden bars' sonic characteristics most closely resemble the western marimba. We are most interested in the resonators of the instrument, which are comprised of graduated gourds suspended beneath each bar similar to the way tuned tubes are used on western mallet instruments. The prominant characteristic of the resonator that we are concerned with is the intentionally added buzz that results when the bar is struck creating a naturally occuring type of distortion. Sympathetic distortion is inherent to African sound design, as these unamplified acoustic instruments must typically be heard above large crowds of people dancing and singing at ceremonies and festivals. The Gyil's distortion is a result of a specific preparation of the gourds where holes are drilled into the sides and covered with a membrane traditionally constructed from the silk of spider egg casings stretched across the opening. In analysing the sonic characteristics of the Gyil, and developing a model, we find that the physical mechanisms through which the characteristic Gyil sound is produced are highly non-linear, and the development of this model has required the use of synthesis techniques novel to physical modelling. We present several variants of our physical model, and conduct comparitive listening tests with musicians who are recognised Gyil virtuosos.