Optimal Live Recording of Timing Nuances by Benjamin Robert Tubb ======================================== Because MIDI's transmission rate of 31,250 bits per second is used as a constant rate for data reception and transfer, Tempo and sequencer PPQN (parts per quarter notes) resolution have variable dependencies of delay times between clock ticks. Because ten bits are required per MIDI byte, the timing delay absolutely limits MIDI's "bandwith" to .33ms (milliseconds) per byte. Consider a Tempo of 60 BPM (beats per minute) and 96 PPQN (as used in the internal sequencers for the XP-50 and XP-80). The clock tick delay time is 10.414ms. Since this is well above MIDI's bandwith, a great deal of timing nuance performance characteristics involving start times and duration is necessarily lost due to "quantisation" at the clock tick "level" alone! To optimize the recording of such nuances for any PPQN, the following chart may be used to allow clock tick delays to be the minimal allowed by MIDI's bandwith and thus better able to record live performances accurately. Because I firmly believe that humans most naturally "feel" rhythms in multiples of 2 and 3, only PPQNs with such "pure" factors are considered. Optimal PPQN/Tempo Settings for Live Recordings (allowing .33ms Clock Tick delays) PPQN Tempo 96 1895 192 948 384 474 768 237 Because three byte events are the most common (as for Note On/Off Controllers, Channel Aftertouchand occasionally four byte Pitch Bend events, but more rarely, system realtime one byte events, a more "practical" use of PPQN/Tempos based on a .96ms (three byte) "resolution" delay could be used with the following results. Optimal Tempo/PPQN Settings for Live Recordings (allowing .96ms Clock Tick delays) PPQN Tempo 96 632 192 316 384 158 768 79 Because the XP synth internal sequencers use 96 PPQN which can't be changed, but the Tempo can be set varied from 10-250 BPM, the highest available recording resolution can be obtained by using the 250 BPM setting which allows a clock tick delay of only 2.5ms although still not "optimal" . Because software sequencers such as Cakewalk have a Tempo range from 0.20 to 250.00 BPM, the setting for 384 PPQN at 158 BPM would be a "compatible" setting for most sequencers and allow the greatest live "naunce" recording available. Benjamin Tubb brtubb@writeme.com http://www.geocities.com/~brtubb http://www.pdmusic.org "Music creates order out of chaos; for rhythm imposes unanimity upon the divergent, melody imposes continuity upon the disjoin- ted, and harmony imposes compatibility upon the incongruous." - Yehudi Menuhin, from "Theme and Variations"