Noise Engineering

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Noise Engineering is a Eurorack and 5U modular synthesizer manufacturer based in Los Angeles, California. 

Starting Out In Modular

This is part of a series of tutorials based on user questions that we seem to get a lot. Are you new to modular and have a question about Eurorack? Are you an advanced user and have burning technical questions?  Please submit ideas for this occasional column here.


Congratulations! You’ve decided to dive into the wonderful world of LEDs, patch cables, knobs, blips, and bloops that is eurorack. But where do you start? This blog post will attempt to demystify the basic concepts that you’ll need to know and guide you through some functions that will be helpful to have in your system starting out. Remember, eurorack is all about creating a system that works for you. There are plenty of popular modules out there, but if they don’t work for you, there’s no reason to have them, even if everyone says you should. We’ll be talking broad concepts as opposed to specific modules as much as possible in this post, and then showing some examples of what we’d want in our own personal systems if we were starting out again; notice that they’re all very different. Again, it’s a personal preference thing.

What is literally the bare minimum you need to make sound with a modular system?

We’ve all seen photos of modular systems that fill a room, and it may seem like you need a ton of modules to do even the simplest thing. That said, to make a sound, you only need one module: an oscillator. Oscillators are free running (meaning they never stop making sound), and you’d need other modules to sequence pitch and control volume, but that said, you can technically make sound with just an oscillator. I’ve done this quite a few times when creating samples and working on sessions: oscillator goes directly into my audio interface and gets recorded into my DAW and then edited further there. Eurorack has some very interesting and unique oscillators, so a single oscillator module can offer a wide palette of sounds not found other places. Going beyond that, there are also “voice” modules (like my all-time favorite module, the Loquelic Iteritas Percido) that include an oscillator, envelope and VCA (more on those later) and act like a traditional synthesizer voice by themselves. In some cases these can be a good starter option as well, but tend to offer less flexibility down the line, so weigh these pros and cons.

Why do people keep freaking out about VCAs?

VCAs, or voltage controlled amplifiers, are an important part of synthesizers that, in fixed-architecture synths, are often hidden from the user. Their name is somewhat misleading: for the most part, they don’t actually make things louder. Remember how earlier I mentioned that oscillators never stop making sound? There are a lot of uses for VCAs, but one of the most common uses of VCAs is to control an oscillator. An envelope can be used to control the level of the VCA, which changes the volume of the oscillator.

So, let’s take a look at what we have so far: an oscillator, a VCA, and an envelope. This is a complete synth voice, but it’s missing an important tool: a way to control all those things. So, let’s go off on another tangent.

CV vs Triggers vs Gates vs Audio

In the Eurorack world, all signals are analog voltages. However, they fall into a few categories. They’re all still voltages, but there are specific behaviors that your analog signal needs to have for some uses. There are four classes of signal you should be familiar with, so we’ll go over that here. Again, they’re all analog voltages, so technically they can all be used for anything, it just may not work well.

Gates:

Gates are a “binary” signal, meaning they’re either high or low. Generally, a gate is used to trigger a voice that’s using an envelope that has a sustain stage (like an ADSR). When the gate goes high, the envelope goes through the attack and decay stages, and then holds at the level set by the sustain. When the gate goes low again, the envelope enters the release stage and falls to zero again.

Triggers:

Triggers are basically really short gates. They can be used for anything that needs a signal to start (a trigger in) but doesn’t have a sustain period. For instance, most percussion modules require triggers, as do low pass gates (more on that later too) and two-stage envelopes (AD or AR). Often, gates can be used in place of triggers (gates are just really long triggers) and triggers can be used instead of gates (triggers are just really short gates…but the difference can really be semantic), but knowing the difference is important.

CV

Broadly, CV (Control Voltage) is used to control everything in Eurorack. For instance, let’s say you have a filter that you want to open and close to change a sound in your patch. You could send it an LFO to slowly modulate it. That LFO signal is a CV signal. There’s also pitch CV, most often created by sequencers, which is a more precise signal used to control the pitch of oscillators. Most oscillators in Eurorack follow the 1v/8va, or one volt per octave, standard. There are a wide variety of CV sources (sequencers, envelopes, LFOs, function generators… the list goes on and on and on) so we’ll go through some useful ones later. Gates and triggers can also be used as CV, since again, it’s all just voltage.

Audio

Audio signals are basically just really fast CV signals. You can’t hear an LFO at .7 hz, but you could hear an oscillator at 70 hz, because they’re the same shape of signal, just in the audio range. Audio-rate signals are used for two things: creating audio (well, duh) and really fast modulation (such as FM and AM synthesis, explained more later).

Meanwhile, back at the ranch

Now that we have a basic idea of control signals in eurorack, we can see what we’re missing: we don’t have any gates or triggers for our envelopes, and we don’t have any pitch CV generators to control / sequence our oscillator. Often, a sequencer module will have both of these things. It will let you program when gates or triggers occur and set notes via pitch CV. Sometimes, you’ll see sequencers that only generate pitch or modulation CV or sequencers that only generate triggers or gates. These can be used together to create the sequencing system of your dreams, or separately for different tasks. In my system, I like having a trigger sequencer for percussion, and a separate gate and CV sequencer for pitched voices. Sequencing is, in my opinion, one of the most personal parts of a system, as everyone likes to interact with their rack differently. There are simple sequencers, such as QuBit’s Octone and our very own Mimetic Digitalis, or complex sequencers like the Winter Modular Eloquencer and the Erica Synths Drum Sequencer. It’s very helpful to find some videos demonstrating a sequencer’s functionality and workflow to see if you  think it would suit you before you commit to buying one, as everyone likes working differently.

For the sake of this rack, I’d probably use something like the Transistor Sounds Labs Stepper Acid. It is very simple to use and is based on a famous sequencer from the 80s. It generates gates and pitch CV, as well as an Accent, which is just another output signal that can be used to make our sequences more dynamic.

Now our rack has an oscillator, an envelope, a VCA, and a trigger and pitch CV sequencer. This is a reasonable starting point, but you might also want a few more modules (or even fewer), or starting with a different patching style. Speaking of different patching styles…

Nobody told me I’d have to learn geography to patch

You may have heard of “east coast” vs. “west coast” synthesis. This makes literally no sense whatsoever, and goes back a few decades to Moog and Buchla, two very important synthesizer manufacturers. Moog (based on the east coast) use a simple, subtractive architecture in most of their synths. This means that an oscillator goes through a filter and harmonics are removed from the signal (hence subtractive), then is dynamically shaped by a VCA and envelopes. Buchla (based on the west coast), however, used a different type of synthesis completely: a “complex” oscillator (basically two oscillators that interact through different means like FM, or frequency modulation) are passed through a low pass gate, or LPG (a VCA and low pass filter controlled by a component called a vactrol) which creates short, percussive, harmonically rich tones that are very different from distinctive Moog sounds.

In eurorack, all types of synthesis are present, including types far beyond the technological limitations of the time when these tropes were established (granular synthesis, now a staple of many modular artist’s setups, requires digital computing, for instance), but the styles of sound are still talked about. However, there’s much more overlap between the two in eurorack; what’s to stop you from feeding a complex oscillator like your Loquelic Iteritas (you have one, right?) through a transistor ladder filter and getting completely new sounds?

Our current rack (oscillator, envelope, VCA, sequencer) could be shifted to be more reflective of “east coast” sensibilities. A LPG like the Make Noise LxD or Rabid Elephant Natural Gate can replace our envelope and VCA (LPGs generally take a trigger in and have VCA, envelope, and filtering built in) and will take our sound in a slightly different direction. If we’ve chosen a simple analog oscillator, that could be replaced with an analog or digital “complex” oscillator like the Make Noise DPO or our LI. Again, these choices are personal and driven by what you want to do with your system, so take some time, do some research, and see what suits you best.

There’s a lot of modules you didn’t talk about here, bud

Eurorack is a vast realm of confusing marketing schemes and convoluted moules, but there’s a lot of fun to be had. Here’s a few more module types that you’ll run into that are useful to understand:

Filters:

They take sound, and they take some stuff out of that sound. They have confusing names like “24dB bandpass” and “2-pole lowpass”. Luckily, we’re here to help demystify things a little bit.

Let’s take that 24dB bandpass filter we mentioned earlier. The number, 24dB, represents how sharp the filter curve is, measured in decibels per octave. That means that in, for instance, a 24dB lowpass filter, the fundamental frequency is 24 decibels louder than the harmonic an octave above it, which is 24 decibels louder than the harmonic above that, and so on. The most common filter slopes you’ll see are 6, 12, 18, and 24dB, with sharper curves slipping in there on occasion. There are a bunch of filter types as well: lowpass, highpass, bandpass, notch, and others. The names just describe what is let through when a signal enters the filter. For instance, a highpass filter lets high frequencies through but cuts low frequencies. A lowpass filter lets low frequencies through and cuts high frequencies. A bandpass filter lets a certain band of frequencies through and cuts lows and highs. A notch filter does the opposite: it lets low and high frequencies through and cuts out a certain band. There are some famous configurations: one of my personal favorites is the 18dB lowpass filter used in the Roland TB-303. There’s a lot to learn about filters, and it’s worth trying out a bunch and eventually finding a few that fit into your rack.

Simple depiction of the main filters you see in eurorack and the relative frequencies that each let pass. Lots more technical info  here

Simple depiction of the main filters you see in eurorack and the relative frequencies that each let pass. Lots more technical info here

DSP:

DSP, or Digital Signal Processing, can be used for almost anything, but is most common for effects like reverbs and delays. There are a lot of different DSP modules but they’re actually some of the more straightforward modules out there. Some of my favorites are the QuBit Nebulae 2, an open-source effects platform with great granular processing; the Strymon Magneto, a crazy delay and looper; and the ZVEX Instant Lofi Junky, a quirky compressor and lofi chorus.

Function Generators:

This is a weird one that you’ll hear about a lot. This goes back to the 50s, when lab equipment was being repurposed to create very early electronic music. In eurorack, function generators generally refer to one of two things: two or three stage envelopes (AD or ASR) or slew limiters. What the gosh darn heck is a slew limiter, you may be asking? That’s a good question. This is a module type that is often over-explained, overutilized, and misrepresented, so you’re in for a bit of a ride. However, the function is simple: let’s say I have a gate signal. I want to use that gate to control a filter opening and closing. If I plug the gate directly into a CV input on my filter, I will get a very sudden opening and then a very sudden closing of that filter, because a gate signal is an on off. If I put my gate through a slew limiter, though, the slew limiter slow down how long it takes to reach the peak of the gate, and then slow down how long it takes to then go back to zero. It basically adds a curve. Slew limiters can be used to add slide to a pitch sequence, smooth out stepped CV, and more. They’ll usually have a parameter for how much slew is added to a rising signal and a separate control for slew on a falling signal as well. Often, function generator modules based around slew limiters will have settings to make them work as simple envelopes or LFOs as well. The most popular module of this type is the Make Noise Maths, which is a dual voltage-controllable slew limiter, four channel signal mixer, and basic logic module. Personally, I really like some of the alternatives: Industrial Music Electronics makes the Double Andre MKII, another dual-channel voltage controlled slew but this time with built in VCAs, feedback, and some other interesting features that take it to the next level for me.

Interestingly, slew limiters aren’t the only modules that can be used to add slew; lowpass filters can be used for a similar function, with slightly different (but useful) results. As you explore patching more, you learn about weird uses for standard modules like this. Modular is a deep, weird rabbit hole. Full of snakes.

Mixers:

Mixers are pretty self explanatory: they mix things together. However, there are different types: AC coupled mixers (meaning they take audio rate signals), DC coupled mixers (meaning they take CV signals), and mixers that handle both. As an aside, any time you see AC or DC, that means a module is intended for audio or for CV, respectively.

As another aside, logic modules can be used to combine gates and triggers, acting sometimes like a mixer (an “or” gate will put out a gate signal any time one of its inputs is high), or utilizing other logic functions sometimes useful for creating different gate and trigger patterns from multiple trigger/gate sources.

A few examples of possible starter systems that you can completely ignore

Do you know ModularGrid? Of course you do. Use it to put together ideas for cases. Images below are cases put together there. Thanks, ModularGrid!

“East” “Coast” “System”

Remember when we talked about east vs. west coast stuff? Here’s an example of a basic “west coast” (or as close as you can get in Eurorack) system, with a MIDI to CV converter, making it easy to control with a DAW or external keyboard.

modulargrid_804892.jpg

Left to right, we have:

This will offer a very traditional sound, but lots can be done with it and having two oscillators means that FM tones and experimental audio-rate modulation is readily available as well. I use a voice very similar to this in my system all the time and it sounds great: two oscillators in the case means you can hard or soft sync which is a sound I absolutely love, and lends itself to a bit of sonic diversity.

The complete polar opposite of that first system

Hopping on a plane and going to the other coast, this is a much more experimental system designed for hands-on playing and experimentation.

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Left to right again:

  • A voltage-controlled clock generator, useful for the two clocked modules in this system

  • Brains and Pressure Points, a very interactive CV generator and sequencer

  • Clep Diaz, a clocked modulation source

  • Cursus Iteritas, a fantastic digital oscillator with endless sound possibilities

  • LxD, a dual-channel LPG

  • Rings, a crazy DSP oscillator and resonator (and a lot of other stuff)

This system offers the polar opposite of the previous, in terms of sound, style, and interaction. A touch keyboard (reminiscent of a Buchla music easel) means hands-on interaction with the system. Multiple CV sources mean ever-changing sound, and a resonator in the form of Rings opens up quite a few new options for a different type of sound than you may normally hear out of CI. It also has some useful hidden modes (including a giant reverb) that are fun to work with.

Personally, if I had to choose between the two, I’d go for this system, simply because it’s much more experimental.

What I’d start out with

I’ve been heavily involved with modular for some years now, both as a hobbyist and professionally, and have a somewhat gargantuan modular system. However, if I had to start all over again and had just 60 hp, here’s something like what I’d want to start out with and why.

modulargrid_804896.jpg

First, the two sequencers and clocking: the Horologic Solum is again my master clock. Mimetic Digitalis can handle four channels of CV for modulation and pitch, and Bin Seq does all triggering/gate duties. My main voice, the incredibly awesome Loquelic Iteritas Percido, takes in CV like nobody’s business, so having both of these sequencers available will allow me to use it much closer to its fullest potential. The Polaris is a compact multimode filter with lots of modes for a wide variety of filtering and shaping options. I then have the Happy Nerding Tritone, a three band EQ that can also act as an overdrive, and the WMD MSCL, a small analog compressor. I’m a production and pro audio junkie so having some interesting mixing utilities like this in the rack is very appealing to me and will help shape and change the sound of the system immensely. Lastly, I put a 2hp Verb in just for some space; reverb is always cool, right?

I have quite a few modules that I have a hard time working without at this point and only a few of them would fit in a system this size, but this small system would still be a lot of fun.

Kris also put together a tiny 60 hp:


modulargrid_805249.jpg

One more time, left to right:

Horologic Solum still serves as master clock. There’s a 2hp mult because that’s usually handy somewhere. Our Mimetic Sequent and expander serve as random CV source because that can be super fun if you just want to explore. The Xaoc Batumi is so incredibly versatile for LFOs I don’t want to live without it. Our new Pons Asinorum and Roti Pola are LFO/envelope generation and mixing, respectively. The 2hp Pluck and our Manis Iteritas are on oscillator duty. Mutable Warps plays with the sounds and then there is a 2hp mixer, though that could easily be replaced with something else if outboard mixing is an option. This case would optimize LFO and randomization, which can be a fun departure to play with if you typically focus on heavily structured stuff.

Cases and power

Oh, right. One last thing you’ll need: somewhere to actually put your modules and something to make them do stuff. Cases and power is one of the weirder sides of eurorack, and there’s a lot  of debate and fear-mongering that may turn you off completely from the idea of starting a system. However, here’s a couple of suggestions. One of them will probably suit your needs, and you’ll be up and running in no time.

You:

Trick answer: DIY cases are very common in Eurorack (in fact, I think I heard someone talking about them recently…). Rails can be acquired a variety of places, enclosures can be made out of virtually anything, and there are lots of simple power solutions to get your rack going. The Row Power from 4ms is a good option: it’s easy to use, relatively powerful, and also pretty inexpensive.

Doepfer:

My personal favorite case manufacturer. The low-cost 6u and 9u are great starter cases, and while more expensive than DIY, you don’t have to get your hands dirty and you’ll have a good case that should last. I use their larger “monster” roadcases for my personal system, and I like them a lot, mostly for the protection they offer the modules. Cases available at various retailers.

Submodular:

The official demo case of Noise Eng. Submodular cases are a great travel solution if you have a reasonable number of modules. The cases are incredibly lightweight and durable, and we throw them in the overhead bins on any plane and they are great. Choose cases with or without power to suit your needs.

In conclusion

There’s a lot to learn about eurorack, and an encyclopedia-length text could be written about it and still not cover everything. I hope, however, that this has offered some insight into basic functions and modules you may run into, and given some guidance as to what to consider when building your first system.

Is there something we didn’t answer? Something you want to see more coverage on? Hit us up.


Noise Engineering is proudly located in Los Angeles, CA