Because there was no need for the extra range (integer part) nor
precision (fractional part). Remember, this is in the context of an
SMF, where fields can start on any byte boundary, so you have to read
things one byte at a time anyway -- not like, say, an MP4 file where
fields are pre-aligned to tidy boundaries and can be gobbled up into
native data types as-is. So in our case the extra bytes would just
be wasted, and there's a strong general bias against wasting bytes in
SMFs -- since they get used everywhere these days, even for phone
ringtones.
-- Chris
Not that it is much use to talk about it here, by why on earth did they settle on 24x24 instead of 32x32?
Chris Grigg wrote:Just thought I should mention that in the XMF-WG the MMA is considering a file format for the interchange of MIDI+Audio sequencer sessions, using the SMF track format for the sequencer track representation, with the audio clips placed on a MIDI timeline via new SMF meta events for Audio Clip Instance. And that in our discussion of sample-accurate audio clip sync there, the seq companies generally agreed that the audio sample clock should be the timebase master, and that the MIDI timing should be derived from that. However the existing SMF Set Tempo meta event was found to be lacking in resolution, i.e. couldn't guarantee sample-accurate placement of audio clips, so the current proposal is to define a new Set High Resolution Tempo SMF meta event, which would set the number of microseconds per SMF tick (the musical time sprocket hole for SMF), with a 24-bit integer part and a 24-bit fraction part. When you do the math analysis on that, it turns out to gives extremely smooth tempo granularity, way sub-sample timing resolution even for futuristic sample rates, and can still cover an .extremely. wide tempo range for all reasonable ppqn values.
Just FYI.
-- Chris-- Mike Berry Adobe Systems
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