[sdiy] How long should a Trigger pulse be?

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Wed Dec 18 16:54:03 CET 2013


I've found myself asking a similar question regarding the acceptable 
length of DINSYNC (SYNC24) signals for bits of old kit.

A lot of the early Roland stuff only polls digital input lines every 1ms 
or every 2ms,  so in these cases an I/O line would have to stay in each 
state for at least this long to ensure that each state is guaranteed to 
be detected by the CPU.

I guess it comes down to the fact that there are "polling" and 
"interrupting" as methods to detect state changes.  Interrupting should 
catch every edge if set up properly, but polling will only give you a 
discrete picture of what's happening at the sampled time instants.

-Richie,



On 2013-12-18 14:38, Tom Wiltshire wrote:
> 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
> 
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