[sdiy] gate/trigger question

[Happy Harry]

Dear Newbie ;^P

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>From: "Caleb Johnston" <caleb_1 at msn.com>
>To: synth-diy at dropmix.xs4all.nl
>Subject: [sdiy] gate/trigger question
>Date: Thu, 30 May 2002 01:34:58 -0400
>
>Dear Experts,
>
>I am trying to build a trigger/gate signal that will start the ADSR.  I 
>heard that the trigger, which is a short pulse of high voltage, actually 
>starts the ADSR envelope.  And then the gate is somewhat lower in voltage 
>but controls the length of time the note is held.  True?

Usually the voltage level is the same. The gate is sustained for the
length of the input...and the trigger is a 'one-shot' that goes high
at the beginning of the gate.

There are also some 'multi-trigger' units that make a pulse every
time the control voltage changes.

Is this for a keyboard gate and trigger... or for some other input?
Trying to trigger from an external source usually is part of an
envelope follower, so tell us what you want.

>
>If I was building a gate/trigger output and I wanted it to be able to be 
>used by most modular products what you reccommend as the voltages, 
>currents, imped.?

I'd recommend 0-10V levels for gate and trigger... and maybe limit
the output with a 1K series resistor to make it real hard to blow up.

If you needed a 0-5V it would be easy to cut the level down.


>
>Also, any good ideas for circuits as how to get that quick pulse for the 
>trigger before the gate?

If you run the gate through a series capacitor...and then through a resistor 
to ground that will make a differentiator... it will output
a narrow positive pulse when the gate goes high, and a negative pulse
(unwanted) when the gate goes low. A diode connected to this output
(cathode to the output, anode to ground) will clamp the unwanted
pulse and make it reset quicker.  I'd start with a .1uF and 10K resistor 
here...  should be about a 1ms trigger pulse.

H^) harry

>
>thanks in advance,
>cj (newbie)
>
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