[sdiy] How long should a Trigger pulse be?

[Dave Brown]

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