ï~~TIMEWARP: A GRAPHICAL TOOL FOR THE CONTROL OF POLYPHONIC SMOOTHLY VARYING TEMPOS John MacCallum, Andrew Schmeder Center for New Music and Audio Technologies Department of Music University of California, Berkeley {john, andy}@cnmat.berkeley.edu ABSTRACT 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. 1. INTRODUCTION Since the beginning of the 20th century, much compositional energy has been devoted to the exploration of timevarying tempos and compositions where multiple players perform in different, but constant tempos. As early as 1930, Henry Cowell recognized that technology could come to the aid of the composer/performer who wished to explore rhythmic complexity when he commissioned Ldon Theremin to construct the Rhythmicon or Polyrhythmophone. Notable attempts to explore this world without the aid of technology include lannis Xenakis' Pldades (1979) and G6rard Grisey's Tempus ex Machina (1979) both of which require that the individual performers play in slightly different tempos (as close as two metronome clicks apart!) so that their parts gradually "slide" apart. Another notable work is the third movement of Gy6rgy Ligeti's Kammerkonzert (1969-70) in which the conductor beats a different tempo for each player and leaves them to continue playing at that speed. The resulting rhythmic texture is of course completely dependent on the ability of the conductor to conjure up the correct tempos and that of each player to continue in the given tempo without deviation, indifferent to the rhythmic chaos surrounding them. In this case, there is much that the computer could do to aid in 'It should be noted that metronomes now often used to aid in the performance of both Xenakis' Plifades and Grisey's Tempus ex Machina. the performance of the Kammerkonzert depending on the goals of the ensemble. One would be right to question the appropriate level of accuracy-is the piece about machinelike precision, or man's struggle to achieve it? Individual click-tracks for the ensemble and conductor, all set to begin at precisely the same time and hold their tempos with machine-precision, would satisfy the former, while a single click-track in the ear of the conductor that would not only change tempo, but could perhaps prepare the conductor with subdivisions that reflect the coming tempo would leave the matter of precision in the hands of the performers who would be left to struggle to maintain their tempos. The tempo canons of Nancarrow beg similar questions of intent-one should be tempted to ask if Nancarrow would have preferred the accuracy afforded by the computer, or whether the slight imperfections in his piano roll would have suited him better. In either case, the tool that we present in this paper makes the construction of such canons trivial. Edmund Campion's ADKOM (A Different Kind of Measure) 2 (2001-present, commissioned by the Drumming Ensemble of Porto, Portugal) for percussion quartet, developed at (CNMAT) with the aid of Musical Systems Designer Matthew Wright, requires a separate click-track for each performer. The tempos in these click-tracks vary over the course of the piece, at times resulting in extremely complex polyrhythms due to their divergence, and at other times causing the performers to come into phase with incredible accuracy that is all but impossible to achieve without the aid of technology. Finally, John MacCallum's... almost like hail... for solo percussion and live electronics contains tempo maps realized by the computer that far exceed the limits of human performability. These are heard as the performer struggles to achieve machine-like precision while following his own tempo map. 2http://cnmat.berkeley.edu/node/7713 373
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