The purpose of this study was to (a) objectively measure and analyze performance deviations from mechanical regularity for three jazz pianists via MIDI-based "groove quantize" procedures and (b) measure how experts rate musical examples incorporating these deviations as being representative of the swing style. The "groove quantize" software procedure was used to measure performance deviations from mechanical regularity for (a) note placements (timings), (b) note durations (articulations), and (c) note velocities (dynamics) contained in 281 measures from 33 performances by three professional jazz pianists. Differences among the performers and for relationships between the performance variables and tempi were measured. Performance models or "grooves" were developed representative of each performer's style and a general swing style. For comparison, "mechanical" models were constructed on the basis of mathematical ratios. Forty-two judges rated the "swing representativeness" of an unaltered melody from each pianist and seven variations of each, four based on the derived performance models and three based on the mechanical model. Analysis revealed that four derived performance model variations were rated significantly more representative of the swing style than were the mechanical variations. Swing ratings did not differ significantly between an unaltered melody and variations based on individual performance models for two of the performers, suggesting that they were representative grooves.
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