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13.6 The di ff erence between a gate and a trigger signal
In my conversations with Modular Synthesizer newbies, the question arises every now and
then about what the difference is between a gate signal and a trigger signal. The subject
can be a bit confusing, because you usually give a gate signal to an ADSR envelope and
still talk about trigging the envelope.
With the help of two drawings it quickly becomes clear what the difference is:
While the gate signal holds a voltage of 5 volts until the key is released, a trigger signal will
only produce a short pulse that is completely independent of the duration of the sound.
For ADSR envelope control this difference is very important. The envelope phases can
basically only be completed if a key is pressed long enough and the envelope receives a
gate signal while it is being pressed. Only then does it go through the attack and decay
phases and rest in the sustain phase until the key is released and the envelope transitions
to the release phase.
The behaviour is quite different if only one trigger signal is received. If the attack time is set
very short, the envelope with the trigger signal can at least output their maximum level
briefly, but then go directly into the decay (release) phase. When driving a trigger signal you
will notice that the envelope settings of the decay phase and the sustain level no longer
have any influence on the sound. You can extend the envelope by extending the release
phase.
However, if the transient (Attack) time is set to a high value, there may be no signal from
the envelope when triggering, because the short trigger is then insufficient to bring the
output voltage of the envelope to a relevant level. The decay (release) phase always starts
at the voltage level that the envelope last had. In the case of a gate control, this is usually
the holding level; when triggered by a trigger signal, it has the reached the level of the
attack phase.
This behavior can be used musically. Create a sound with a sustain level of 0, a short
attack time of 0, and a moderate decay time. The release time, however, is set long.
If you play the sound longer, you get a short, percussive sound. Holding the gate signal
causes the sound to be brought to the sustain level of 0 volts with a short decay time. The
subsequent release time does not change this because it starts from the zero level of the
sustain phase. If, on the other hand, you send a very short GATE time - ie only touch the
note - the release phase joins directly to the attack phase, resulting in a much longer sound
history. This allows you to manipulate the curve of the envelope over the gate time.
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Without Interpolation With Interpolation
Voltage
key
pressed
key
released
5Volt
GATE SIGNAL
time time
Notelength
Voltage
Key
pressed
key
released
5Volt
Trigger-Impulse
Notelength