The vast majority of synths made today have two primary types of control voltages :
CVs and gates.
The CV is for pitch & gates are used to fire envelopes.
Most Eurorack modules output a 1V/oct pitch voltage, and a +5V gate.
Korg and old Yamahas use Hz but that's another story.
jack as my gate input.
This mostly worked as long as I had a +10V gate.
And if you had installed a gate booster you could boost those
pesky Eurorack +5v voltages to keep the ARP happy.
In most cases the AR & ADSR envelope generators are used to control the filter & VCA.
They can also be used to modulate other sections such as the VCOs.
The AR has a constant sustain (it's open as long as you press a key).
The AR envelope is not prewired to the VCOs so we need to use a patch cable to use it.
It is however prewired to the VCA.
The AR has a linear shape, vs the ADSR which is exponential.
So if you want the volume to change "naturally" use the ADSR
This is the basic setting for connecting a sequencer/keyboard to the 2600.
For about 10 years I mostly ignored those two jacks next to the S/H Gate thinking they were just
gate & trigger outputs from the ARP 2600 keyboard (which they are) since the arrows pointed out.
Actually, they are also inputs !! ... that is they are bi-directional.
After a bit of research I learnt that the old ARP 2600 (& ARP2500) use an almost forgotten system of triggering envelopes.
They use both triggers & gates.
How does this work?
The ADSR is as you'd expect.
Here is a common envelope shape when using a a trigger & gate
The "trigger" is the envelope's cue to start the ball rolling but it won't do anything
unless it also sees a gate (in the above drawing its the spike at zero time).
ATTACK
When a gate signal is applied, the EG's output will rise exponentially to 10V
(the rate is determined by the "attack" setting).
DECAY
When 10V is reached, the attack phase is ended, and the voltage will decay exponentially to the Sustain level. (the rate is determined by the "initial decay time" setting). In modern synths, we just call this the "decay".
SUSTAIN
The sustain level is adjustable from zero to 10V
The output remains at the sustain level until the gate is removed.
RELEASE
When the gate is removed, the voltage drops to zero volts.
This is called the "Final Decay Time".
The rate of the drop is exponential and is determined by the "Final Decay Time" setting.
another gate is inputed. In this case the envelope will then restart the attack phase.
This system of gates & triggers makes very complex envelopes possible
If you don't have a sequencer with both triggers and gates
you can "trick" the 2600 by plugging into both the trigger & gate jacks the same gate signal.
I've tried this with a Arturia keystep and it works fine.
Another option is to set two VCOs into LFO mode.
I like to use a pulse for the gate, and a saw for the trigger.
It works too !
This is from the ARP sequencer manual:
Notice the triggers and gates.
The 1601 & 1613 sequencer has a unique gate bus that allows mixing of Gate and "triggers".
Another sequencer to use is the Klee.
It also uses a bus that mixes gates & triggers.
This unusual keyboard apart from the Ondes Martenot ring controller has CV, Gate and trigger outputs.
Other possibilites in the world of eurorack include
ALM Busy Circuits ASQ1
Or just combine a CV/Gate sequencer with a percussion sequencer.
(plenty out there)
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