CV, Gate, Trigger and Audio
There are a few different signal types so it’s worth familiarising yourself with them to properly understand how to get patching. Audio is probably the simplest to get your head around: this is a produced sound that can be heard. For example, an oscillator produces audio signal, you plug that into the Audio In on a filter and there’s an output that produces the resulting, effected audio.
CV stands for controlled voltage and comes in a few different forms, too. If we want to modulate said filter, we can take an LFO or an envelope and plug their output (not an audio signal) into the CV control. This is a continuous signal that isn’t heard, but its effect is.
Gates and triggers are both binary signals that can be represented as pulse waves. Where as triggers are a short blip indicating clock divisions or triggering a drum machine, gates are note on/note off informing how long an envelope should stay open, for example:
Here we can see the note on information is the red dotted line, and note off is the blue. Audio signals are at an audio rate (20 Hz to 20 kHz) and can be heard as a sound in the form of an alternating current (AC) which has an audible frequency (pitch) and amplitude (volume).
CV signal is direct current (DC) and could be pitch information, an LFO, envelope or any other modulation source.
Gates are high when a note is depressed and low when it’s released. This would normally come from a keyboard rather than a sequencer.
In this example the trigger hits at the same time as the gate but is momentary. Triggers could also be plugged into a sequencer with clock information, but we’ll cover that in more depth another time.
Modules by Type
As mentioned earlier, it’s probably worth having at least a basic understanding of synthesis and signal flow before delving head first into modular world but it’s by no-means necessary as modular is a fantastic way to learn about synthesis if you’re just starting out. Let’s start out with some basics i.e. modules that are the same in the modular world as they are in the plugin world.
VCO (Voltage-Controlled Oscillator)
Sine, Triangle, Pulse or Sawtooth – you need a sound source in order to started shaping your sounds. One big difference between modular and what you might get in a plugin is that oscillators are always running: if you plug one into a mixer you’ll hear a sound, regardless of whether or not you trigger it (we’ll cover more on this later).
A number of companies make great oscillators: Doepfer, Pittsburgh Modular and MFB are among the cheaper options where as intellijel, Make Noise and Mutable Instruments offer some more interesting alternatives, albeit with a larger price tag attached to them.
VCF (Voltage-Controlled Filter)
Filters are common-place in modular systems. They work by removing certain overtones and harmonics from an audio signal. The usual suspects can be found here, low, high and band pass, as well as less common filter types like all-pass and comb.
All filters contain different components so will have different sweet spots and react to different modulation sources, especially with the resonance cranked up.
*There was a link to here to a fantastic Doepfer Filter ‘shoot-out’ but it’s since been removed. Ed.
You should be familiar with envelopes if you’ve dealt with synthesizers in some capacity before: attack, decay, sustain and release parameters can shape our amplitude, pitch, filters and really just about anything that has a CV input.
Function generators are a name given to loopable stages of an envelope, so an AD or AR envelope that loops could be described as a function generator. Make Noise’s MATHS is probably the Don Corleone of this genre, being so flexible and multifunctional. Worth reading more about it than me trying to describe its many talents:
LFO (Low-Frequency Oscillator)
…or LFOs, as they’re abbreviated, are used as modulation sources to control parameters such as amplitude, pitch, filter or (like envelopes) just about anything. Typically they operate below 20 Hz but some can run into audio rate for frequency modulation effects.
Look out for dual LFOs, LFOs with phase restart/cycle retrigger, ones with voltage controlled frequency modulation, noise and random waveforms etc.
VCA (Voltage-Controlled Amplifier)
Seemingly an uninteresting module at first, these things are actually gold dust as probably everyone on Muff Wiggler will tell you. Really it’s an amplifier that we can use to control the volume of our patch with an envelope (via a keyboard or a sequencer) or an LFO but it’s really so much more than that; I’ll try and cover it more another day.
VCAs come in linear (for CV) and exponential (for audio) forms. This refers to the curvature of the slopes that modulation sources would provide. You don’t have to stick to this recommendation, though, and look out for VCAs that handle both like this Doepfer one.
MIDI to CV
If you want to play your modular like a keyboard, you’ll need to interface with it via MIDI. There are a few of these on the market; I opted for the Kenton Solo (as I had the desktop version already) but Doepfer, Pittsburgh Modular and Mutable instruments all offer similar capabilities, with Expert Sleepers taking it a step further with their desktop software.
The two outputs of a MIDI to CV module are pitch CV (1V/oct as opposed to other analog synths that might use hertz per volt) and gate. The former connects to oscillators as well as key tracking on filters whereas the latter trigger envelopes. Additionally, you can take clock information from a DAW such as Logic or Ableton and control sequencers – more on this later.
Read more about CV and gate on the Wiki.
Drum modules are not something I’ve gotten into. Personally, I prefer to keep this in Ableton but that doesn’t mean it’s not something I’ll explore more in the future.
TipTop Audio offer decent clones of the Roland TR series of modules while hexinverter have some more customisable options. Usually drum modules require triggers from sequencers. Lately, Bastl Instruments have entered the Eurorack market with an incredible looking drum system:
A big top topic, which will be covered in in more depth in later articles. There are basically two types of sequencers so, like our MIDI to CV modules, we can get sequencers for CV and sequencers for gate (or triggers).
Pitch sequencers normally have rotary pots and come in 4-, 8- or even 16-step variations. I have a trusty Pittsburgh Modular Sequencer but Make Noise, intellijel and Xaoc Devices all offer more advanced alternatives.
Gate or trigger sequencers work by outputting positive or negative signals such as +5v(olts) or 0v at regular intervals, to either trigger a drum machine or an envelope. These can range from simpler devices, like Doepfer’s A-160 or the 4ms clock dividers and multipliers, to Euclidean sequencers like the Rebel Technology Στοιχεῖα or ALM’s Pamela’s Workout: