KRW1%LEHIGH.BITNET@IBM1.CC.Lehigh.EDU (04/07/90)
There is an ambiguity in the MIDI file spec regarding the handling of tempo changes. It is not specified whether event deltas should refer to a time interval computed at the time of the previous event and in the current time base, or whether the time interval must account for any tempo changes (and thus delta unit size changes) during the time span preceding the event. For example, say at time 0 an event delta is given as 8 units, with a unit defined as 10 microseconds. If after 4 units the tempo is doubled (halving the unit size), should the event occur at time 80, or 60? Does anyone know whether this has ever been clarified, or know what the original intention was? I suspect that both interpretations may have been used in programs which write MIDI files. -- Kevin ------------------------------------------------------------------------ Kevin Weiner Lehigh University Computing Center (215) 758-3991
smhall@peg.UUCP (04/13/90)
There is a meta-event (ff 51 03 tttttt) that changes the tempo on page 11 of the SMF spec. . If you 'hard-code' tempo changes in the sequence, you have changed it. All sequencers deal with tempo as an entity unrelated to the sequence's note lengths. I think the deltas should reflect the note's value (1/8,1/4 ...) relative to the "ticks per quarter note" in the header chunk. steve hall