Drum Trigger Signals

[Byron G Jacquot]

> Can someone tell me what they know about drum trigger signals? From what I
> know, its a short pulse signal. I am wondering about how long and what
> voltage should the pulse be etc.
> 
> Specifically, the 808 BD circuit I am looking at has inputs for a trigger
> and an accent signal...
> Since I dont have the luxury of owning an 808, I cant scope these signals to
> see how they are formatted.
> 
> I understand that a lot of this is depends on the drum circuit, but any info
> would be appreciated.

With a Twin-T circuit like the 808, the circuit is sensitive to state
changes on the input.  You can drive them from a square-wave LFO, and
they'll trigger (really just a ringing filter) on every transition:
either on or off.

It's more common to drive them from narrow pulses.  The circuit will
resonat on the rising edge, and the falling edge occurs before the
original drum sound is over, so it doesn't retrigger.

The really cool thing about Twin-Ts: the voltage change in the pulse
translates directly to the amplitude of the resultant sound.  A bigger
pulse in makes it louder.  I don't have the schems right in front of me,
but I think the older Roland drum machines simply add the trigger pulse
to the instrument pulse to make it bigger, making the drum louder when
it's hit by both signals.  Anyone care to corroborate?

Byron