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HOW TO: Understanding Synth Gates and Triggers

December 22, 2016

If you’ve worked with synthesizers, specifically the analog variety, you’ve undoubtedly used gate or trigger signals. Understanding these signals is a basic requirement for using a modular synthesizer, a virtual modular, interfacing gear, and a number of other instruments in a typical studio, even electronic drums.

BACK IN THE DAY

When some of the first analog synthesizers were being designed in the ’60s by the likes of Bob Moog and others, it was obvious from the start that several types of signals were needed to control the various aspects of the instrument. One of the major advancements during this time was voltage control, which allows the output of one circuit to control parameters of another in real time, effectively automating changes of a sound. Voltage control uses a variable voltage to control a variable parameter, like an expression pedal provides variable control over volume.

But another signal was needed—an On/Off signal to indicate a key had been pressed, to start a sequence, or to activate individual drum beats. In many early systems, this signal was called Trigger. The name implies a quick signal marking the start of an event, but in many cases this signal indicates a start by turning On, then an end by turning Off. This applies nicely to keyboard keys being pressed then released. Most modern synthesizers call this signal Gate.

Fig. 1. In a keyboard controller, a bus wire is shared by all keys and each key makes contact to ground to produce a single, shared On/Off Trigger signal.
The first versions of Trigger signals were not voltages but a switch to ground; these were called Switch-Triggers, or S-Trig for short. The benefit of an S-Trig is that multiple devices can short the signal to ground in parallel without additional circuitry. In a keyboard controller, for example, a bus wire is shared by all keys and each key makes contact to ground to produce a single, shared On/Off Trigger signal (see Figure 1).

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