The Q109 Envelope Generator!
When I press a key on my keyboard (through my Q104 MIDI-to-CV converter module) it generates a gate signal. This is a pretty simple on/off signal - when the key's pressed, it's on. When the key isn't pressed, it's off - not that nuanced if we're trying to make dynamic musical sounds, as that sounds that we're used to hearing from normal instruments tend to fade in and out, or have certain ways of attacking before decaying and fading away. The envelope generator takes this boring on/off gate signal and imparts a four-part countoured curve to it.
Those four parts of the envelope are Attack time, Decay time, Sustain Level, and Release Time, or "ADSR." ADSR Envelopes are pretty much the standard on traditional analogue synthesizers, though the original Minimoog only had a three-part envelope. Some synths (like the Casio CZ series in the eighties) have attempted to employ more complicated multi-stage envelopes, but the good old classic ADSR always seems to win out for quick, intuitive, and useful control of sounds. While the Synthesizers.com system uses knobs for its envelope section, many synths, like my Roland System 100, use sliders (pictured below). I have to admit that I prefer using sliders when it comes to setting envelopes because I feel like you get a more visual representation of the shape of the envelope, but I've adjusted to the DotCom's knob system.
If you take a look at the picture of the module at the beginning of this entry, you can see that each of these parameters has its own dedicated knob used for setting its value. "Attack" determines whether the signal fades in slowly (long or high attack value) or triggers immediately (short or no attack). After the signal reaches its highest level in the Attack phase, the Decay phase begins, in which the signal falls over the amount of time set by the Decay knob until it reaches to the Sustain point or Sustain level, the level at which it holds or sustains as long as the key is held down. Once the key is released, the Release phase begins, in which the signal fades out over the amount of time set by the release knob; long release means a long, slow fade out, while a short or 0 release means that it drops to nothingness immediately when the key is released.
Confusing, huh? It can be, but work with an envelope generator for just a few minutes and it becomes immediately intuitive, which is what matters.
Moog literature often refers to envelopes as "invisible hands" that can be programmed to turn knobs on a synth, and I think that's a great description for the practical applications of an envelope module. You see, an envelope generator doesn't make any sound on its own; it's a control module, meant to be used to control other modules in the system. By patching the gate in from the keyboard into the Envelope's input, then patching the output to an amplifier or filter, I can use the envelope's "invisible hands" to control how the amp or filter behaves when I press a key.
Here's some examples! All of the examples below use the basic sawtooth wave through the amplifier module, or through the filter, then amplifier module.
1. Normally, the oscillator's sound just drones on and on, but when I patch it into the amplifier, I can taper the sound down until I hear nothing. Then, I patch the envelope to control the amplifier's volume when I press a key. Depending on the settings of the envelope, the volume of the sound will behave differently over time. Here's a few little melodies.
This one has no attack, no release, no sustain, and a very short decay. You immediately hear the notes, and then they quickly fade out, like a plucked instrument.
Longer attacks and releases here; the sound fades in and fades out slowly.
Everything at 0 except Sustain, which is all the way up. Key press = note. Key release = silence. Not much nuance until the end, when I turn up the release so that the final notes fade out more naturally.
2. Now, let's use the envelope on the filter module instead of the amplifier! Normally, I'd move the filter cutoff knob to affect the sound as described in the Filter entry, but I can patch the envelope up so that its "invisible hands" will move the filter cutoff knob in accordance with the envelope setting. Let's do it!
Shorter Attack and Release settings sweep the cutoff when I hit notes, before I turn the Attack and Release up all the way for a few long, slow, eerie filter sweeps.
A shorter attack and then quick decay with zero sustain and release makes a brassy sound that quickly "opens up" as the note is played like the splatting and blatting of a tuba or trombone...
...while even shorter settings make it faster, fartier, and funkier.
By now, you should be getting a good idea of how the envelope affects the way that things behave - and this is only scratching the surface of its applications in even such a basic system. I could patch the envelope to control the oscillator's pitch, making it rise and fall with each key press, or I could even patch it to the pulse width input of the pulse wave so that it could change the shape of the pulse while over time (pulse width modulation). Instead of using the oscillator, we could repeat #1 and #2 but patch the noise source into the amplifier and filter, then use the envelope to contour the noise source's sound. Hissing white noise quickly becomes a cymbal or wind, while pink noise quickly becomes a snare drum or gunshot when the envelope is modulating the amplifier that the noise runs through. Many people use several envelopes in a modular system; the general rule is one envelope for each amplifer at the very least, but many people like to have several so that one can control the way the sound's volume behaves while the other controls the filter. Even better, once we get Multiples involved (next installment, coming soon!), one envelope's output can be sent to several different modules at once so that they all simultaneously respond to the envelope's shape when a key is pressed.
Well, that's more than enough for now. I've already received a multiple and my second oscillator, so the next two installments are covered, and I'd like to give Pulse Width Modulation and Modulation (aka "Stupid two-oscillator tricks") their own entries as well, exploring the real craziness that having two (or more) oscillators adds to the mix. I'll also be posting some music I've made with this little setup once I get this Cubase problem worked out (again, if anyone can help with that, I'd really appreciate it!). I've already made a dubby track, a hip hop one, and a Moroder-esque four-on-the-floor dance track, all 100% created with the DotCom system. Until then!