Getting Started with Modular Synths in 2025: How They Work

When actually using a filter module, you need to input some sound (apart from self-oscillation), so the sound also needs to be patched into the filter via a separate cable. We've patched this using actual modules. From the left, there's the sampler 4ms Sampler (sound source), Hikari Instruments Dual LFO (LFO), and Hikari Ping Filter (filter) module.

The blue cable is the patch that passes the LFO voltage above, and the red is the patch that inputs the sound from the sampler to the filter. The yellow is the output of the filtered sound, which goes to the speaker or headphones via a mixer or audio interface. However,The audio output of a modular synth is higher than normal line level.Therefore, it is recommended to use a separate output module to convert it to line level (see hereCategoriespart of which is the output module).

When you press the top center button of the sampler module, the sound inside the sampler is triggered and output. The filter cutoff is constantly modulated by the LFO, so you should hear the sampler sound periodically getting brighter and darker. In the world of modular synths, this sample triggering is also usually done with voltage. To trigger a sample, all you need is to express ON/OFF switching, so a signal that switches between two types of voltage is often used. A signal for this ON/OFF expression isGate signalIt is a type of CV, but is sometimes referred to separately as "CV gate."

Gate signals are often output from keyboards or sequencer modules to control the timing of sounds and the length of sustain.

Gate signal. Used as ON/OFF.

またLFO square waveSince the voltage shape is the same, the gate signal (ク ロ ッ クIt can be used asIf the voltage is the same, other modules can perform the same function.This is also a feature of modularity.

LFO and VCO pulse waves also repeat ON/OFF, so they can often be used as a periodically occurring gate (called a clock).

So far we have shown you voltages such as LFOs, gate signals, and clock signals, but modular synths can also create a variety of other control voltage shapes.

It is a type of CVenvelopeIf you patch this to a VCA, you can change the volume in this way.

It changes to a random voltage at regular intervals and keeps that voltage until the next timing.Random voltageIf the voltage does not change in a stepped manner but fluctuates continuously, it is still called random voltage.

Playing sound sources with a controller

Here, we will consider the case where you want to use a controller such as a keyboard to send CV to play a sound source such as a monosynth or sampler, and explain what kind of controller and monosynth to use.

MIDI note and CV/Gate correspondence

When playing a non-modular synth externally,MIDI Notesis typically sent to a synthesizer.

• Note ON/OFF
• Pitch
• Velocity

It is composed of the following elements:If we create a control voltage that corresponds to the most important pitch and note ON/OFF information, we should be able to create a CV signal that can be used like a MIDI note. Unlike MIDI, CV can only send one control signal per cable, so we need patches that correspond to pitch and note ON/OFF separately.

Note ON/OFFis easy,Gate signalSo what about the CV of the pitch?

Pitchis the sound sourcefrequencySince the pitch of a sound is 12 notes, and in order to control it with voltage, the VCOs, synth voices, samplers, and other sound sources in modular synthesizers always have a frequency control jack, but if the input voltage is changed continuously, the frequency also changes continuously, making it possible to produce frequencies between the XNUMX notes. This is fine if you're creating sounds that don't care about the pitch, but there will also be situations where you need frequencies that can only take on fixed pitch values.

The frequencyExactly matches the 12-tone scaleTo achieve this, it is necessary to standardize how much the frequency changes depending on the magnitude of the input voltage, and then the input voltage must be discrete values ​​that correspond to each musical scale according to that standard.

In EurorackThe actual frequency CV input specifications are:A 1V increase in input voltage raises the frequency by one octave (doubles the frequency)So, this type of input1V / Oct inputIf you are using a keyboard module as a controller, the pitch CV is designed to increase by 1V (1/1V semitone up) when you play a key one octave higher according to the standard. In other words, to output a frequency CV according to the musical scale, you need to set the output CV to the corresponding pitch for each key.It is necessary to approach the voltage discontinuitiesThis function allows you to adjust the CV to a specified scale.QuantizerThis can be found built into keyboards and sequencer modules, or you can use a dedicated quantizer module to tune the pitch.

*The quantizer is also a useful function when automatically playing a modular synth. By using an external quantizer, you can continuously generate pitch CV corresponding to a melody from an LFO or random voltage without using a sequencer or keyboard. Although it is an advanced topic, the basics of automatic playing patches using LFOs and quantizers can be found inThis articlePlease also refer to

A typical example of the gate voltage and pitch CV changes that control a sound source is shown below. The top is the gate voltage, and the bottom is the pitch CV. To prevent the pitch from changing during the release of the sound, the pitch changes the moment the gate turns ON, and that voltage is maintained until the next gate is input.

Various controllers

In this way, to control a synth with CV, at the very least, you need something like the aboveYou need to send a pitch CV and a gate signal.Typical sources of pitch CV/gate in a modular are:

• Sequencer Module: CV/Gate sequencer that allows you to program pitch CV and gate ON/OFF for each step. Whether or not a quantizer is included depends on the model.
• Keyboard module: It outputs the corresponding pitch CV and gate according to the pressed key or touch plate.
• MIDI to CV and Gate conversion module: This is a MIDI to CV module. It can convert from simple to various Cc, and some can even process polyphony. Creating a polyphonic synth using a purely analog modular system is difficult because it requires moving a large number of CV/Gate inputs in a way that supports polyphony. If you want polyphony, please use a MIDI to CV conversion module that converts MIDI to CV/Gate with the correct voice allocation.
• Standalone keyboard: Arturia Keystep or similar with pitch CV and gate outputs

Sound source side settings

Next, let's consider the configuration of the module that receives the pitch CV and gate signals and produces sound. In a sampler module, the sampler itself typically has a gate input that triggers the sound and a V/Oct input that controls the pitch.In the case of modular monosynths, it is common to build them up from even smaller components rather than using a single synth module.

1. VCO
2. VCA
3. envelope

You can create such a voice with just these three things. For a specific patch that uses these VCO, VCA, and envelope to create a synth voice, please see my previous blog post,"What is Control Voltage (CV)?" .

Creating a synth from these minimal components is the basis of traditional modular synths, but some people may find it a little difficult to understand how the VCA works, and it's a bit cumbersome that the pitch CV needs to be sent to the VCO and the gate signal to the envelope, two signals that need to be sent to separate modules.

In fact, even with modular synths, you can break down each function to its minimum and select modules one by one, or you can use a single module to create a normal synth.synth voiceSome are equipped with all of the VCO/VCA/envelopes mentioned above.Like a sampler, a voice module like this can receive pitch CV and gate in one module, making it easy to understand and reducing the space and patching required. This means you can use it in situations like "I want to play right away rather than do detailed patching!" or "I'm just interested in effects, and any convenient, standard voice for the sound source will do for now!"ALM Busy MCO,Michigan Synth Works BeehiveThis is the voice module.

またSemi-ModularThere are also modules of this type that can be used as a synth without any additional patching, and can be used with separate inputs and outputs on the same module.This type of pedal allows you to further deepen your sound creation. For example,Intellijel Designs Atlantixis a semi-modular synth. Its unique feature is that it has more inputs and outputs than a simple synth voice module, on a par with a full modular system, and allows for experimental patching.

Depending on what you want to do, you can also consider incorporating integrated modules and MIDI devices like those mentioned above to create a setup that works for parts that are too complicated or costly.

About the pitch setting on the sound source

If you want to play only the notes, the controller's output pitch CV must be 1V/Oct and output a voltage corresponding to each note, but the frequency knob on the sound source must also be set properly to ensure the correct note is played.When CV is exactly 0V, CIf you set it so that 1V input to 1V/Oct will produce a C one octave higher, and 1/1V input will produce a C#, so you can play the correct scale.

In modular systems, setting the initial pitch with a knob is like this.tuningIn the case of digital modules, the first note is fixed, such as C, so tuning is not required.When it comes to tuning, it can take some time to get the pitch right, so if you want to avoid that, we recommend using a module that doesn't require tuning.

On the other hand, when 1V is input to the V/Oct input on the sound source side, it is adjusted so that it goes up one octave.Calibrationcalled.New modules from manufacturers are calibrated, so users do not need to do it. Analog calibration is done by adjusting the trimmer on the board, but it is often difficult to do so, so do not touch it casually.

Here we've introduced modular synths and explained the basics of control voltage. In the next post, we'll finally explain how to build a setup!