Synthesizer Patch Bays: A Beginner's Guide

If you feel intimidated by synthesis and patch bays and find you're excusing yourself from conversations about them, now is the time to face your fear and discover your inner synth power.  

Eurorack, Modular, Moog Mother, Model 15, and MS-20 are words that can both excite and intimidate the beginning synthesist. Getting started with a synth or synthesizer modules that include patch bays (or that are completely made up of patch-able modules) can be addictive, creative, frustrating, rewarding, and infuriating all at once. Be warned! Once you start down this rabbit hole of creativity, you may never come out! Here are a few tips to get you on your feet the first time you're faced with a patch bay to connect and no idea of where to start.

Starting On the Same Page

For the purposes of this article, I'm going to utilize the Moog Model 15 app. At $30, if you have an iPad this is the most cost-effective way to get into modular synthesis without having to sell off vital bodily organs to fund your new creative venture. Now, although we'll be using Model 15 as the demo, I'm going to keep the concepts as general as possible. One of the coolest things about using modular synthesizers and patch bays is integrating your general knowledge of synthesis with the customized nature of building a modular beast. Model 15 may be our guinea pig, but these tips should help you get started anywhere. 

Begin at the Source

The first place you should look and locate on your modular setup is your sound source, and your outputs. There's no sense getting hip deep in cables and filters if you're not absolutely positive you have a working sound source and working output path. I've seen plenty of folks wire everything 'by the book' only to pull their hair out when nothing makes any noise. It wasn't until after that they realized they didn't have an output wired properly, or the oscillator module wasn't functioning as it should.

The first thing we'll do is take a sound source (an oscillator) and plug it directly into an output (a trunk line). In Model 15, you can do this by double-tapping one of the wave shape outputs in a 921b oscillator module. If you're in a noisy place, you might want to go with a sawtooth, that's a nice and loud one! Next, double-tap on either of the 'trunk lines' on the right side. Think of the 'trunk lines' as your main outputs that go to your speakers. You should hear a low rumble until you adjust the oscillator's octave switch. The number/foot measurement is derived from the olden days of organ stops, so the smaller the measurement, the higher the pitch. Choose 8', 4', or 2' and you should hear sound no problem.

Plug the sound source (oscillator) into an output (trunk).

Plug the sound source (oscillator) into an output (trunk).

You can also adjust the pitch by rotating the frequency knob. This allows you to access pitches between octaves. You might be wondering when we'll get a standard keyboard in the mix—don't worry, it's coming! Take a moment to enjoy adjusting pitch in this manner, though. Part of the allure of modular synthesis is that you don't have to do everything with a piano keyboard. You can make some great sounds simply by adjusting the oscillator's manually.

Controlling Voltage 

Okay, so you want a little more control and want to get a keyboard controlling your frequency. First, re-read that last sentence and keep in mind, that's all you're really doing. The keyboard is going to make adjustments to the oscillator frequency for you—and eventually be a 'gate' that decides when sound should or should not pass through. We'll set this up in a few stages.

To begin, we will disconnect that droning oscillator from the output and re-connect it to a VCA, or Voltage Controlled Amplifier. Double-tap the cable connected to the trunk line, scroll up a bit, and double-tap a 'signal input' on the 902 VCA module. If this were a physical synthesizer, we'd be unplugging the patch cord and re-plugging it in elsewhere. 

Oscillator to VCA to trunk.

Oscillator to VCA to trunk.

You'll notice the sound disappeared. That's because your sound source is no longer 'making it' to the output. It's going to a VCA and just sitting there. You'll double-tap the VCA's 'signal output' jack, scroll down, then double-tap a trunk line input. The connection is now re-established. You won't hear anything just yet, the VCA isn't amplifying the signal and letting it through yet, but a simple rotation of the 'Fixed Control Voltage' knob will let you hear sound once again. If you want the keyboard to alter the pitch, you'll need to flip on the 'controls to' switches. Have the controls go to the oscillators and the envelope.

It's important to note here that this particular switch is a tad unique to Model 15. On a standard analog modular synth, you'll need to hook up a keyboard that outputs CV (control voltage) to your sound path—or you will need a module that specifically converts MIDI into CV for you. Both are fairly common. 

Once you've got your keyboard outputting control voltage to your VCA, you can reduce the 'Fixed Control Voltage' knob, the VCA will be getting its control voltage from your keyboard now. If you play the keyboard, you should notice the pitches changing, but you'll also notice that the sound sustains indefinitely. In order for the sound to stop when you let go of a key, we will have to set up an envelope.

Lick the Envelope

An envelope basically will shape the voltage in some way. In this case, we want to shape the dynamics or volume of a sound. We want to tell the VCA to allow sound through for a certain amount of time, at a certain speed. Look on the right side of Model 15 and you'll see a pair of 911 Envelope Generators. Double-tap the only output jack of either one, scroll up and find the 'Control Input' on the VCA that you've already set up and double-tap to make the cable connection. 

Envelope to VCA.

Envelope to VCA.

Now, the voltage going through the VCA (and thus, the sound we hear) will be regulated in a shape dictated by the envelope. In other words, we'll hear the sound start and stop in the shape that matches the values we input on the 911 envelope generator. Using T1 and T3 (T meaning 'time') you can adjust the attack and release of the synth sound you've created.

What's Next

Wherever you decide to go next, I hope you keep the tenets of what we've done here in mind. There are many tutorials for Model 15 built into the app, but very few of them go into why you're plugging in what you're plugging in. I highly recommend checking out our course on Model 15, as learning the methodology behind why certain signal paths will alter sound in certain ways can help you transport this knowledge to any analog synth you want!

Learn more about synthesis in the Ask.Audio Academy.

Matt Vanacoro is one of New York’s premier musicans. Matt has collaborated as a keyboardist in studio and on stage with artists such as Jordan Rudess (Dream Theater), Mark Wood (Trans-Siberian Orchestra), Mark Rivera (Billy Joel Band), Aaron Carter, Amy Regan, Jay Azzolina, Marcus Ratzenboeck (Tantric), KeKe Palmer, C-Note, Jordan Knig... Read More

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