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Eurorack Delay: Introduction to Synth Delay Effects and The Coma Reactor 2 Textural Delay Module

Delay – one of the essential effects in the synthesist’s arsenal, originated with the spread of magnetic tape recording in the 1950s. Adding a delay unit to your modular synthesizer...

Crating Space and Texture with Delay on Eurorack

Delay – one of the essential effects in the synthesist’s arsenal, originated with the spread of magnetic tape recording in the 1950s. Adding a delay unit to your modular synthesizer setup can open up a new portal of creative possibility. In this article, we’ll look at the basics of delay, explore some of its creative uses, and introduce the Coma Reactor 2 – one of the best Eurorack delay modules around.

Coma Reactor 2 Eurorack Delay Module – Buy Now on the AFA Store

What Is Delay in Music?

What is Delay? Graphic illustrating the concept of delay in audio signals.

The definition of delay in music is as follows: Delay in the context of music production is a time-based effect that creates an impression of an echo or repetition of the original sound. Traditionally, it is created by playing a delayed version of the sound after the original, resulting in a distinct, repeated pattern.

Delay vs. Reverb

New-comers to audio and music production often ask “what's the difference between reverb and delay?”. To put it simply, the difference between reverb and delay is that although both are time-based effects, delay is a series of delayed repetitions of the original signal; while reverb is a more complex effect that simulates the acoustic properties of a physical space. Unlike delay, reverb does not produce distinct repetitions of the sound.

How to Use Delay?

Delay can be used to add depth and space to a mix by creating a sense of movement. It is a good way to add complexity and texture to your sound by adjusting various parameters such as its timing, feedback, and tone. Understanding delay effects will open up numerous new sound-shaping possibilities with your Eurorack setup, for example, here are some creative ways you can use delay in music or sound design.

  1. Creating Space: Delay can help create a sense of space and dimension. A good example is found in the Aphex Twin track “Windowlicker”. Delayed sounds bounce back and forth between the left and right channel in the mix, creating a mesmerizing spatial effect.

  2. Adding Texture: Modulate delay times and feedback levels to add texture and complexity to the mix. Delayed sounds can be further filtered and distorted to create tactile atmosphere in your soundscape.

  3. Emphasizing Rhythm: Add delay to certain elements in your mix to create unique rhythmic effects as in the classic Daft Punk track “One More Time”, which features delayed vocals with a staccato feel. Another great example of delay creating a rhythmic effect is the doubling of the iconic bassline in Donna Summer's "I Feel Love".

  4. Special Effects: Use delay creatively to create interesting sounds such as tape-style pitch wobbles, slap-back echo, or rhythmic stutter.

  5. Enhancing Transitions: Delay can help you smoothy transition between different sections of your composition while still maintaining a sense of cohesion, making it a handy tool on stage as well as in the studio.

The Coma Reactor Eurorack Delay Module

Coma Reactor II – One of the best delay modules for Eurorack

The Coma Reactor is a delay module based on the famous PT2399 – an iconic chip known for its gritty, low-fi sound. But the Coma Reactor isn’t just another basic delay effect. The module takes delay on Eurorack to the next level through unique signal routing possibilities, independent dry/wet volume controls, and a FX loop. Topped with CV inputs for delay time and filter frequency, the Coma Reactor lets you set up your patches for anything between mild tape-echo warbles to seasick pitch shifting.

A Send/Return path allows for further processing of the delay signal through external modules, while a CV controllable bandpass filter lets you finesse the soundscape to your heart’s content.

The Coma Reactor is also capable of generating noises on its own with no input connected thanks to its ability to self-oscillate. Cranking the resonance on the bandpass filter will also create oscillation, resulting in ambient mayhem. This makes the little 12HP module a handy addition to your rack with the creative noise-making opportunities it provides.

How to Use the Coma Reactor in Your Eurorack Setup

The Coma Reactor is easy and fun to get the hang of. Start by simply patching your audio signal into the module and crank up the Coma, Time, and Feedback knobs. From there, you can keep things simple or go completely bonkers. The Coma Reactor truly expands your rack’s sound design capabilities with unique controls such as –

  1. Independent Dry and Wet Volume Controls:
    Vary the level of processed vs. unprocessed signal in your mix. Be as subtle or unhinged as you please!

  2. Return Level:
    Take an output from the Send jack and feed an externally processed signal back through the Return input. Fine tune the return level for complete control of your mix.

  3. Filter Frequency, Filter CV, and Resonance:
    If nothing is connected to the Send/Return jacks, there is a nasty built in bandpass filter for you to mess with. Shape your tone by changing the frequency of the band-pass filter in the return path. You can also add a CV source to modulate the filter and bring your patch to life. Turning up the resonance will increase the chance of self-oscillation, making the Coma a sound source in its own right. Note that these controls will do nothing
    if there is an external effect connected to the return jack.

  4. Return Feedback:
    Control the amount of effected signal going back into the delay circuit and the FX Send. This lets you drive the Coma Reactor into self-oscillation very easily, making it behave as a unique sound source as well as a delay.

  5. Feedback:
    Primarily used to control the amount of repeats, you can also crank this up for some crazy, delirious self-oscillation.

  6. Coma:
    Use this control to attenuate the input, or turn it up for some sweet overdrive sound.

  7. Time and Time CV:
    Set the delay time interval to your liking or add a CV source for some lively modulation. The Time CV control, like Frequency CV, allows attenuation and inversion of the CV input to suit your CV source as well as your desired modulation amount. Changing the time will also create pitch shifting effects. 



Introducing Delay in your modular synthesizer setup is a great way to experiment with time, space, and texture in your synth patches. The Coma Reactor is a powerful tool for achieving your sound design goals or just facilitating creative sonic exploration with your Eurorack setup. This makes it one of the best Eurorack delay module for explorative sound synthesis.


Coma Reactor 2 – Buy Now on The AFA Modular Synth Store


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