MIDI hardware timing devices

[The Dark force of dance]

Y-ellow Marc-Julien.
	
At 05:43 PM 04/19/99 -0600, Marc-Julien Objois wrote:

[big snip here]

>So going from one PIT value to another would produce relatively large
>jumps in bpm, and there was no way of setting it to accurate bpm
>values.  So how is timing achieved in _real_ hardware?  What does the
>A3k do to playback a sequence?  BTW, I never even _touched_ MIDI
>timecode.  And active sensing?  Well, I threw that out the window before
>it even got to my MIDI queue...  :)

I don't use the motorola stuff. I'm a MCS51 kinda guy. That's for more
practical and financial reasons but that's not important here. Whilst I
haven't done what you're suggesting yet I will need to do this in the near
future. On a theoretical level however, what you need to produce is a
software generated phase locked loop. Or in television parlance a flywheel
circuit. This allows you to lock at a higher resolution than the MIDI sync
affords. As I said, I have not done this yet on a practical level but I can
assume this is not exactly an easy thing to achieve. Or more to the point.
Achieve well.

You have 24 pulses per quarter note. You need something more like  120. So
you need to multiply this by 5 but each new pulse needs to be evenly spaced
and that's where the tricky bit starts.  It's actually a case of trial and
error but it's a matter of how fast, or within how many clock pulses can
your software lock on. If you look at a real PLL you'll see it does exactly
this anyway. Only your job is to do it all in software.

I had actually considered doing it outboard  in a real-world PLL but I'm
not sure that is exactly the most elegant solution.

BTW: I'm not one of the gurus of this list, they know who they are. :) I
just happen to be working in this field right at the moment.

Hope this helps.

Be absolutely Icebox. 

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