Most of you probably own a guitar pedal, that offers an expression input. Some of you might actually use an expression pedal to control your expression-ready pedal. Or you might possess a synthesizer with one or multiple CV inputs. But what's the difference between Expression and CV? Let's try to explain this in a single sentence: Expression is just replacing or adding a resistance source in series with the original resistance in a pedals or instruments circuit, while CV or Control Voltage is actually sending an AC signal.
Think of it as passive (expression) and active (CV). A synth with a CV input is expecting an active AC voltage. The most common voltage range is 0-5V, but different companies use other ranges like 0-8V, 0-10V or bipolar CV. Expression on the other hand works differently: Most expression pedals out there expect a reference voltage from the device it’s connected to, divides that voltage down by a certain amount and then feeds it back to the device. This is most commonly accomplished with a TRS (tip / ring / sleeve) 1/4″ cable where the reference voltage is on the “ring,” the control voltage is fed back to the device on the “tip” and the “sleeve” is ground. Different companies use different values for the pots inside their expression pedals – 10K, 50K, 100K and others. Because in these most common cases, the pots act as voltage dividers, the values don't matter that much.
While this concept might work for pedal pots that are wired as a voltage divider within the circuit, it's a bit less simple for pots that are wired a variable resistance. In this case, you could connect an expression pedal, that uses a TS cable, but the value of the pot inside the expression pedal is crucial, since it needs to match the value of the pot it connects to. This means, that you would need a specific TS expression pedal for every guitar pedal with an expression input connected to a pot wired as a variable resistance. Unless all these guitar pedal pots have the same value – which is highly unlikely.
In conclusion, this also means that you cannot modify each guitar pedal to accept an expression signal that easily, based on the fact that you simply cannot control how the guitar pedal pots are wired. If you know your way around building and modifying circuits, luckily there are ways to make all wiring cases work. By using a vactrol, you could transform an expression signal into a variable resistance. But it still means stacking an additional circuit onto the guitar pedals' existing one.
In light of these revelations, CV might feel like a much easier concept, and in terms of setup, it maybe is. But keep in mind that CV means sending an active AC voltage to a pedal or instrument, and if the receiver of this voltage is not catered to it, the damage could be done.
All pain, no gain...?
Until now, we made a good case of advocating against both expression and CV. If you're not an experienced circuit builder, your safest bet is to just go with what the industry tells you and carefully read your pedal and synthesizer manuals, so you don't cause any damage by trying to connect the wrong expression or CV sources.
But if you manage to sail past these do's and don'ts, expression and CV will open up a sea of sounds for you. There must be a reason why CV is back to being a hot topic with the revival of analogue synthesizers and the boom of Eurorack modular systems, and at the same time more and more boutique pedal builders incorporate expression and cv inputs into their pedal circuits.
Using expression and CV is fun, exploratory and might even help you breaching your stuck-in-a-rut sound vocabulary. Yes, it's an old concept, and it hasn't really evolved since its emergence, but that also means you have a bottomless bucket of information, ideas and helpful tips at hand.
The perfect accomplice
Because we love the underlying concept of CV/expression, we had this idea of building a utility tool that can do both – without limiting itself in terms of creativity. The brainchild of this idea is called Lewis, the standalone LFO Expression modulator. It enables you to control all of your pedals, synthesizers or Eurorack modules – no matter if they expect expression or CV – via an integrated LFO, that can be shaped and formed with different onboard controls.
The beauty of Lewis is its plug and play functionality: you don't need to worry about CV voltages, pot values or wirings, Lewis does everything for you. Our recommendation: if you own anything with an expression or a CV input, you need to at least have a look at Lewis. We're pretty sure you're gonna like him.