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e c———i——t——ati———on—— J. MacCallum and A. Schmeder. Timewarp: A graphical tool for the control of polyphonic smoothly varying tempos. In Proceedings of the International Computer Music Conference, 2010. d——ow———nl——o——a—d——— We present a parametric method for the variable control of tempo with specification of shape and phase alignment constraints, and its implementation as a graphical interface written in C for the Max/MSP environment. This tool aids in the construction and management of polyphonic streams of independent, fixed or smoothly-varying tempos suitable for live performance or computer-generated scores. We also present a brief history of how polyphonic tempo manipulation has been used in context and compare our work with two recent projects to implement similar tools.