Noise Engineering

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User questions: Triggers vs. Gates 101

This is the first in a series of tutorials based on user questions that we seem to get a lot. Are you new to modular and have a question about Eurorack? Are you an advanced user and still have burning questions?  Please submit ideas for this occasional column here.

A question I get a lot when I talk to new users (and indeed one that took me a while to wrap my own head around) is the difference between triggers and gates. The short answer is that triggers and gates are in the eye of the receiver: it's entirely a semantic distinction. The more in-depth answer is that the difference really lies in how the module looks at the signal. In fact, a signal can be both a trigger and a gate!

I used this post as an excuse to fire up the oscilloscope that Stephen handed down to me to generate a couple of helpful images.  I used the Noise Engineering Sinclastic Empulatrix, which has a switch to allow you to toggle between gate and trigger modes. In either case, the module responds to a clock input and outputs an envelope, but how it does that is different in each mode.

Let's look at how SE behaves in trigger mode.


When the clock signal goes high (yellow), SE detects a rising edge and this triggers an envelope (green).  The attack on the module was set to fast, so in this case, the green line shoots straight up to its maximum and then releases pretty quickly.  

Compare that with what happens in gate mode:


The front end is similar: the module detects a rising edge from the clock and so it starts the attack of the envelope. But in gate mode, it doesn't immediately drop off. Instead it continues to output a high voltage until the clock signal drops off (the falling edge). When it does, the envelope releases. The period of time where the gate remains high is called sustain in envelope terminology. 

Some modules can meaningfully distinguish between triggers and gates, and others do not. Some modules have gate mode and trigger mode and those will allow you to really play around and get a more intuitive feel for the distinction yourself if you don't happen to have an oscilloscope or a scope module at your disposal.

Stay tuned to the Noise Engineering blog for an upcoming post of what you can do with those cool triggers and gates, and so much more. And if you have questions you'd like to see here, please drop us a line.

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