For reasons that should be obvious, we call Triggers and Gates timing signals, and every synth needs them. But why both? Surely the Gate is performing the trigger function, and the Trigger itself is unnecessary? This is a question that dogged me for many years, until I was fortunate enough to have both a Minimoog and an ARP Odyssey sitting next to each other in my 'live' keyboard rig. I often used these to play a heavily contoured solo sound, with an instantaneous (Attack = 0) percussive 'spike' of loudness and brightness at the start of each note. This spike was, of course, created by applying a pair of contours to the VCF and VCA.
Strangely, and despite the outstanding reputation of the Minimoog's contour generators, I knew that I preferred to play my fast solos on the Odyssey, but I did not know why. All I knew was that my playing sounded punchier on the Odyssey, and that I could play at higher speeds than I could on the Minimoog. The reason for this was nothing to do with my playing (I was rubbish on both) nor was it anything to do with the relative quality of the instruments' keyboards. The answer lay in the engineering within the instruments: the Odyssey uses triggers, while the Minimoog does not.
Look at Figure 8.
This shows what happens when I play lines very quickly on an Odyssey. As you can see, the notes overlap because I can't remove my fingers quickly enough from previous notes before playing the next. But you can also see that the contour remains dynamic, and that the start of each note is clearly defined. This is because the Odyssey re-triggers its transient generators every time I play a note, regardless of whether previous ones are released or not, and regardless of whether the Gate is Open or not. This means that my sounds are correctly articulated, no matter how unevenly I release the keys.
Let's contrast this with the Minimoog, a synthesizer that does not generate triggers. Its single, unconventional timing signal is called an S-Trigger, but is, in fact, a Gate. So the same line played identically on the Minimoog produces the filter and amplitude contour shown in Figure 9.
As you can see, the envelope is far less interesting and, although you will still hear the second and successive notes at the sustain level, the punch is lost. The synth solo becomes dull and uninteresting, and the audience remains unimpressed. Indeed, the only way to recapture the dynamics and punch of the Odyssey solo would be to release each note before the next, and I have already admitted that I am not capable of that at high speed. Consequently, for average players rattling off fast solos at the limits of their abilities, the Odyssey is superior to the Minimoog (the fact that the Odyssey keyboard is duophonic and the Minimoog's is monophonic also helps, but that's a topic for another day).
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