[sdiy] MIDI arpeggiators (Was: trying to ... late 70's synths)

[Matthew Smith]

Quoth George Hearn at 2009-01-05 18:32...
> ..I didn't mention MIDI clock synchronization in my last mail so I thought
> I'd add my thoughts...  I personally prefer it if the arpeggiator always
> starts from 0 time when a key is pressed for the first time, keeping time
> with the MIDI clock, but not necessarily beat synced to it, others may
> prefer to have a hard synchronization with the MIDI clock, where arpeggiator
> notes always play dead on MIDI clock pulses.  This however I found gave a
> bit of an un-natural feel when playing, others may hear it differently.

My thought would be to provide a means whereby notes may be triggered 
slighly off-beat if a less "robotic" sound is required.

A delay is simple - just use a timer that is triggered by the incoming 
clock that sounds the next note when it expires.

Getting the note to sound slightly /before/ the beat is a bit more 
tricky as this would mean timing two beats and then having the timer 
trigger notes at the duration of one beat less the required amount - 
effectively triggering the notes just short of a beat behind.  The 
potential issue here would arise if there were a change in tempo which 
could make the delay before triggering the note get out of kilter.

One possible solution to this would be to count the time between /every/ 
pair of clock messages and constantly update the required delay.  (Clock 
messages come along 24 times every 1/4 note, if I remember correctly.) 
   I think that a fairly fast device would be required to keep up with 
this AND all the other things that that arpeggiator would need to do.  A 
second microcontroller, sharing the MIDI input, could be used just to 
keep track of tempo - a possible solution to the possible problem caused 
by the possible solution ;-)

Cheers

M


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Matthew Smith
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