Amplification (VCAs) and Envelopes – Continuing the Basic Modules of Synthesis

I mentioned last time that I’d be covering filters and envelopes in this post, but after receiving the rest of my components and working with them this week, I began to feel like I should, perhaps, change that to amplification and envelopes, as amplification is an even more basic piece of the puzzle. Not to worry, I’ll get to filters in the next post or so.

Voltage Controlled Amplifiers (VCA)

WMD Multimode VCASimply put, amplifiers make quiet sounds louder. Strangely enough, the contrary is also true when it comes to VCAs, they can attenuate the signal, as well. Perhaps, a better phrase for these would be Voltage Controlled Dynamics. In modulars (and pretty much every other kind of analog synth), we use voltage to control how loud the sound is. We can even vary the voltage to create tremolo, a repetitive raising and lowering of volume which can give various sensations from stuttering to long, flowing waves of sound. One of the simplest effects, it was the very first effects pedal brought to market, with the DeArmond Model 60 Tremolo Control. And, yes, I have one.

Author’s Note: The DeArmond Model 60 (A & B) used fluid resistance to vary the volume, not voltage control. I was just pointing to how cool an effect something so simple could be.

 It’s true, the VCA is a simple tool; however, keep in mind that the crazy and incredible minds out there have found some cool things to do with the VCA. For instance, the WMD Multimode VCA allows you to deal with not one, but two signals simultaneously. It also allows you to use one or two control voltages to control both or each signal, respectively. It also allows you to use a CV to crossfade between the two signals in a couple of ways. It’s a very versatile tool, especially in stereo and multi-channel environments. WMD is not the only manufacturer with great VCAs, checkout tons of them at Analogue HavenControl, or, better yet, at a local shop, if you’re lucky enough to have one.

Envelope Generators (EGs)

Since we’ve already gone over envelope generators in The Basics of an Analog Synthesizer, we know how they can generate CV to control something like the WMD Multimode VCA and others. So, I’ll devote this section to looking at what ingenious minds have added to make some of the more evolved EGs special.

Circuit Abbey ADSRJr + Expansion

Circuit Abbey ADSRjr ADSRjrExpFirst off, let’s take a look at the Circuit Abbey ADSRJr + Expansion. If you look at just the ADSRJr without the Expansion, you’ll see just the basics of the ADSR envelope generator, a gate input, four knobs to adjust attack, decay, sustain, release, and a CV output.

There are two other buttons there, though. First is the time button that allows you to choose short, medium, or long times for the parameters. For instance, for percussive sounds, you may want a super-tight response, so the short setting might be best. However, if you’re doing ambient work, the long setting may be appropriate. It will give you those extremely long, luxurious attacks that swell and decay slowly. Then, there’s the in-between, medium setting for the rest.

Also, one of the handiest things on any EG is the button below the release knob. On the ADSRJr, it’s called Cycl (for Cycle, get it?). This allows you to have the envelope cycle over and over again. When you’re working just with the modular and no keyboard, I cannot overstate how handy this is for previewing and testing your envelopes. Also, it can be used to create a complex LFO pattern.

REMEMBER THIS!!! When you buy an EG, always try to get one with a trigger or cycle button on it. It is one of the handiest things you’ll use on a modular.

So, that’s the ADSRJr, a pretty straightforward ADSR EG. So, let’s take a look at the Expansion and what it does. First, you’ll notice that we have a LOT of CV I/O. There are inputs for ADSR which allow you to control any stage of the envelope via CV, AWESOME! Next, you have a set of buttons labelled “curve” with A, D, and R next to them. These buttons change the way the voltage changes between these stages. Without these buttons, the CV goes to the next level in a straight line (linear). That’s not always the most natural or musical sounding, as ears do not hear in a linear fashion, even though most EGs operate this way. If you press the button, next to one of the letters, that portion of the envelope will change from linear to exponential, which means that it will approach the next value in an exponential curve, moving slowly at first, then accelerating rapidly to the final volume. Notice that there isn’t a button for sustain, as sustain is just the level at the end of decay and is active for as long as the gate is “high.” Okay, that’s a pretty nice addition, more natural sounding envelopes that you can control via CV. And just beneath the curve buttons is…wait for it… a trigger button for manually firing the envelope, very nice.

But, the Expansion goes further, still. There are three trigger outputs labeled EOA, EOD, EOR. Get this…these fire at the end of their respective stages. So, if you want your sound to evolve by, say, mixing in other sounds at the end of the attack or decay or if you’d like to fire a second envelope at the end of this envelope, these trigger outputs will do the job for you. Pretty badass, huh?

Finally, there are two more features, a trigger input to fire one full cycle of ADSR and an inverted output. “Inverted output?” you say. “Yes, inverted output.” I say. What this does is to flip the envelope upside down. So, if you’re using the envelop to drive frequency of a VCO, a filter, or some other type of module, instead of attack going up, it will go down, decay will come back up, and release will rise to the pre-attack position.

WMD Multimode Envelope + Expansion

WMD Multimode Envelope + ExpansionThe WMD Multimode Envelope + Expansion is quite similar to the Circuit Abbey ADSRJr + Expansion, but has a few very nice additional features. First, let’s go over the similarities. You’ll find attack, decay, sustain, release knobs on the front panel above the gate/trigger and 0-8V out (CV out). On the Expansion, you’ll find all the CV inputs for the various stages, along with EOA, EOD, EOR triggers. You’ll also notice a Manual button, which is effectively a trigger button on the main panel.

Now, let’s look at the differences. If we look at the WMD MME main unit, you’ll also see a set of 4 knobs that control the shape of the stage. Remember the buttons that went from linear to exponential on the ADSRJr+Expansion? Well the MME allows not only that, but also logarithmic curves, too, and anything in between. So, you can choose your A, D, and R to go from fast to slow as it approaches maximum, static velocity, or slow to fast. Nice, huh? There’s also a trigger on end of sustain, which is a nice extra. There are also what are called full-swing outputs. Basically, these are CV outputs that swing from -8V to +8V during the cycle and vice-versa. This can be useful when acting like a complex LFO.

Oh, wait. There’s one more knob here. There are a ton of labels on it like ADSR, ADR, AR, ADAR, ADSAR, ADSRst, ADRcy… Well, let’s just call this the Amazing Knob. This knob allows you to choose what type of envelope you want. It supports the normal envelopes like ADSR, AR, ADR (note that any envelope without the ‘S’ in it is a triggered envelope. It fires, but doesn’t hold the note since there’s no sustain portion). It also supports rearranging these a little with envelopes like ADAR, and ADSAR.

The coolness doesn’t stop there, though. The envelopes that you see with ‘st’ following them are step-based envelopes. Each time it receives a trigger signal, it will perform the next step of the envelope and stay there, only proceeding when it receives another trigger. The envelopes with ‘cy’ following them are cycling enveloped. Once you start them, they will run indefinitely, firing over and over, as if you took the EOR trigger and patched it to the Retrig input. This is some serious awesomeness.

Now, let’s slip over to the Expansion side of things. Over here, you’ll notice that there are three more inputs (Retrig, Hold, and ADR Time Scale) and a switch (Reset on Gate). Retrig simply listens for a trigger and restarts the envelope from the beginning. Hold, well that does just what you might think. When a gate is sent to Hold, then the EG stops right where it is until the gate is low again, then continues where it left off. ADR Time Scale is a little different, though. ADR Time Scale allows you to send a CV to the EG that will adjust how long the A, D, and R stages are simultaneously. I haven’t quite had use for this, yet, but it seems pretty neat, and I expect I’ll find it cool when I do.

Now, let’s talk about that switch, Reset on Gate. In order to understand this one, we need to discuss how analog synths play. Since keyboards are inherently mono-timbral, i.e. they can only communicate which pitch and when to play, not what sound to make, they send a voltage (which key was pressed) and gate (that a key is pressed). A traditional analog keyboard was effectively a long set of resistors running the length of the keyboard. Each key was effectively a short circuit that would either increase or decrease the number of resistors the control voltage would have to go through, and, thus, was not only mono-timbral, but also monophonic (one note). So, in its resting state with no keys pressed, no current would flow, the gate would remain low (off), and the envelopes would not fire. As soon as you pressed a key, the gate would rise, signaling the envelope to open, and the control voltage that was governed by which key was pressed would control the pitch of the oscillator.

So, what happens if you press another key before you release the previous one? The pitch control voltage changes, but there’s nothing to cause the gate to come down, thus starting the release cycle of the envelope. The answer? In the old days, nothing would happen with the envelope. It would stay in its sustain phase since the gate remained high (on).

Skip to November 1981, when Dave Smith and Chet Wood presented what would become the MIDI standard to AES. All of a sudden, we had a standard way to tell synths from various manufacturers how to play multiple notes at the same time. There were some proprietary methods before MIDI, but none became the standard. In any case, each note effectively had its own start and end, not just a gate for the entirety of the keyboard. So, now when we use our handy-dandy MIDI to CV converters in order to play our modular synths with our MIDI keyboards, we can tell these envelopes to re-trigger by sending a new gate signal for each note played.

And that’s the long answer to what the Reset on Gate button does. It is very handy, indeed.

In Conclusion

I think it’s pretty obvious how important VCAs and EGs are to your modular world, at this point. Honestly, you can’t have too many of them, and you can use them in any number of ways. The two I’ve presented above I’ve been very happy with over the last week, but other manufacturers have wonderful additions, as well. I’m sure I’ll be adding more to the arsenal.

Now that I have the modular up and running, I’m hoping to start including some audio in these things, but the day has gotten away from me, and I want to play now. Bye bye.

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