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Re: MIDI tick resolution

From: karl
Subject: Re: MIDI tick resolution
Date: Wed, 21 Mar 2018 13:32:40 +0100 (CET)

> Also keep in mind that tick resolution is given in pulses per quarter note
> (PPQ), not seconds. This means that a slow piece will have a lower
> resolution /in true time/, i.e. ticks per second.

I don't think resolution /in true time/ matters, since each tick is 
"exact" in some sense.

What matters is the smallest subdivision of a quarter note used
(unless you use the smpte time format).

> Finally note that the
> reference is a quarter note, so if you have 384 PPQ, you then have 192 ticks
> per eighth note, 96 per sixteenth note, 48 per thirty-second-notes. Given
> that contemporary music can very much look like the image below, I think
> there is a strong case for higher PPQ in order to have decent
> representations of tuplets of very short note values:
> <> 

(My wild guess is that music would need a tick value of 64*9*5*7.)

The technical limitation of midi file format is that the tick is a 
15bit quantity, i.e. the maximum value is 2^15-1 = 32767.
(Instead of "ticks" you could use a time code based time, guess that 
that is more for film making, don't know much about that.)

So you can't get 128*9*5*7 = 40320, but 64*9*5*7 = 20160 is possible, 
and if you really need 128*9*5*7*11 or whatever, then you either need 
 to choose a format other than midi,
 accept (smallish) time errors or
 you have to scale the notes, say make a quarter a whole note or longa
  (that would gain you a factor of 4 or 16).

All note times in the file is delta times, and they are of variable 
length; the largest number allowed is 0x0FFFFFFF = 268435455, so if your
tick is 2^15 (finest subdivision), the longest time is slightly less 
than 8192 quarter notes, which should be sufficient for most (all?)

In effect, there is no need to choose a small tick value unless you 
want smaller midi files (a consern which should be irrelevant today)
or perhaps due to some misbehaving midi equipment.

/Karl Hammar

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