[sdiy] How long should a Trigger pulse be?

[Tom Wiltshire]

Many of you have raised the same point, which is that gear that polls the input is likely to be much slower to respond than either analog gear or gear that uses an interrupt to detect changes, In this regard, the early microprocessor-based stuff is probably the worst case scenario, where the inputs are polled in round robin style at a fairly <yawn> slow rate.

I'm not particularly interested in designing something that works for the worst-case scenario, especially if that's some rare/special piece of gear from the 80's that had a desperately overloaded processor. If it works on most gear most of the time, that's fine with me.

It sounds like I can't go much below 1ms without starting to run into problems, if I'm summarising correctly. And even that might be a problem for the 1980's polled input synths - but I think that's probably that's their problem, not mine.

Thanks to all,
Tom


On 18 Dec 2013, at 19:11, "Dave Brown" <davebr at earthlink.net> wrote:

> I've always used 5 mS for the stuff I've designed.  I don't remember exactly
> why I picked this number but it works well with microprocessor-based modules
> that poll for a trigger.  My ARP 3604 Keyboard outputs an 80 uS trigger.  I
> would suspect any vintage gear would work with a short trigger as it is most
> likely edge sensitive or used as a set (or reset) input.
> 
> My ARP keyboard had another issue that caused problems with some gear.  The
> gate is used to generate the trigger pulse so the gate goes true before the
> trigger pulse (I don't remember by how much).  I ended up adding a D flip
> flop with the trigger as the clock and the gate as the reset-0 to
> synchronize them.
> 
> Dave
> Modularsynthesis.com
> 
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Tom Wiltshire
> Sent: Wednesday, December 18, 2013 6:38 AM
> To: synthdiy diy
> Subject: [sdiy] How long should a Trigger pulse be?
> 
> Hi All,
> 
> I'd like the benefit of your combined experience, if I may.
> 
> I'm decoding MIDI Note On/Offs and outputting Gate and Trigger pulses to
> drive envelopes. My own envelope designs don't need a very long trigger
> pulse in order to fire, but I thought perhaps some others do.
> 
> Currently I'm using 500us Triggers, but I don't have a big pile of old
> synths here to try that on, so I don't know how well that will work on
> vintage gear.
> 
> And then of course, there's the problem of envelopes or synths that don't
> have a Trigger input...
> I remember the Kenton Pro-2 MIDI-to-CV convertor had a "retrigger" mode
> where it dropped the Gate briefly to allow Gate-only envelopes or synths to
> retrigger. It didn't say how long it dropped the gate for though. I'd
> thought to do something similar with the following circuit:
> 
> http://www.electricdruid.net/GateAndTriggerCircuit.png
> 
> This converts Gate and Trigger into a Gate-with-gaps that will retrigger a
> Gate-only envelope. And this is the main reason for my asking the question;
> In this case, the output gate is essentially delayed by the length of the
> trigger pulse, hence my desire to keep it as short as possible. If it wasn't
> for that, I'd just use 5ms and reckon that'd trigger anything.
> 
> So, oh wise ones of Synth DIY, how short can my trigger pulse be?
> 
> Thanks,
> Tom
> 
> 
>