The "Black Atlantic" rhythmic diaspora, be it realized in jazz, blues, gospel, reggae, rock, candombléé, cumbia, hip-hop or whatever, seems to have widespread capacity to facilitate dance, engagement, social interaction, expression and catharsis. This article examines the reasons for this. Black Atlantic rhythm is founded on the idea of groove or feel, which forms a kinetic framework for reliable prediction of events and time pattern communication, its power cemented by repetition and engendered movement. Overlaid on this are characteristic devices that include syncopation, overlay,displacement, off-beat phrasing, polyrhythm/polymeter, hocketing, heterophony, swing, speech-based rhythms, and call-and-response. Using an evolutionary argument, I point out here that nearly all of these have at their heart the establishment of perceptual multiplicity or rivalry, affecting expectation, which acts as either a message or a message enhancement technique (via increased engagement and focusing of attention), or both. The causal path for the remaining devices is based on adopting structures shared with speech, notably prosody, conversational interaction, and narrative. Several examples illustrate how, particularly in jazz and jazz-related forms, extensions and relatively complex creative adaptations of traditional African and African diasporic rhythmic techniques are a natural consequence of a culture of questioning and reflection that encompasses maintenance of historical reference and accommodation to innovation.
Two short pieces of freely improvised music by the same performer were recorded in microstructural detail by the use of a specially constructed automatic transcription apparatus. The apparatus consists of a modified DX7 synthesizer and 2650 microprocessor which interfaces with other computers for data processing. The resultant music is transcribed into a modified form of traditional notation and subjected to both micro- and macrostructural analysis. Microanalysis includes the areas of timing (interonset and duration distributions, displacement, chordal spreads, etc.), dynamics ( key velocity, quantization, chordal patterns, etc.), and legatoness (relative, absolute, pedaling). Macroanalysis uses the full panoply of devices from traditional music theory (tonal procedures, rhythmic and motivic design, pitch class sets, etc.). Correlations between microstructural parameters, and with macrostructure, were found to be highly significant in Improvisation A, which had a supplied external pulse, but largely absent in Improvisation B, which had no such pulse. Where pulse was present, rhythmic design was found to be based largely on pulse subdivision and shifting. Some performance effects (e.g., chordal spreads) operated over a time scale of 10 msec or less. Others (e.g., synchronization to an external pulse) showed less resolution. Differences in the distribution patterns of interonset times, durations, and legatoness suggest three independent underlying temporal mechanisms that may sometimes link together in coordination with macrostructure. Quantization ("categorical production") of some variables (interonset times, key velocities) was clearly established. The results were also interpreted in relation to an earlier model of improvisation (Pressing, 1987).