Direct and surrogate sensing for the Gyil african xylophone

The Gyil is a pentatonic African wooden xylophone with 14-15 keys. The work described in this paper has been motivated by three applications: computer analysis of Gyil performance, live improvised electro-acoustic music incorporating the Gyil, and hybrid sampling and physical mod-eling. In all three of these cases, detailed information about what is played on the Gyil needs to be digitally captured in real-time. We describe a direct sensing apparatus that can be used to achieve this. It is based on contact microphones and is informed by the specific characteristics of the Gyil. An alternative approach based on indirect acquisition is to apply polyphonic transcription on the signal acquired by a microphone without requiring the instrument to be modified. The direct sensing apparatus we have developed can be used to acquire ground truth for evaluating different approaches to polyphonic transcription and help create a ``surrogate'' sensor. Some initial results comparing different strategies to polyphonic transcription are presented.