Source Audio Intros C4, A ‘Eurorack Modular Synth in a Pedal’

Source Audio are releasing the C4 Synth, a four-voiced synthesizer pedal for guitar and bass. The pedal’s creators say the pedal pulls together “all the sound creation tools of a classic Eurorack modular synthesizer and packages them in … an effects pedal.”

The C4 Synth pedal features six synth effects, with tracking abilities, and fast response. For additional effects, the Neuro Desktop Editor (a free download for Mac and Windows) and Neuro Mobile App (free for iPhone and Android) offer a library of presets created by the the Source Audio team and the C4 Neuro community.

The C4 comes with over 120 presets, Source Audio President Roger Smith estimates that number will grow to 1000 within the month. The simple means by which the C4 Synth user can browse and play the library of sounds, burn a handful of favorites directly to the pedal, and then bring them to their next gig in a small, simple to use package, says Smith, is unprecedented in synth pedals.

Burning presets to the C4 Synth pedal requires a connection to the Neuro Editor, after which, musicians can browse presets on the pedal for testing. Favorite presets are saved with a single click to one of the pedal’s six toggle switch positions or 128 MIDI-accessible positions.

The C4 Synth pedal features a simple 4-knob control panel (two of the knobs are dual-function) that includes Input Level, Envelope Sensitivity, Wet/Dry Mix, Master Output Level, and two knobs labeled “Control 1” and “Control 2” that adjust different parameters, depending on the preset. The C4 comes pre-loaded with six synth presets, and also includes 56-bit signal processing, a compact anodized aluminum housing, stereo inputs and outputs, and a mini USB port that receives MIDI messages from DAW (digital audio workstation) software as well as external MIDI controllers with USB host support. The C4 can also receive MIDI CC messages when connected to the Neuro Hub (also sold by Source Audio).

For deep editing on the C4, the Neuro Desktop Editor and Neuro Mobile App offer a wide set of modular synth-inspired sound sculpting tools. The Sound Editor includes four assignable voices, three oscillator wave shapes (sine, square, saw), >10 envelope followers, >20 modulating filters, distortion, tremolo, pitch shifting, intelligent harmonization, FM synthesis, two programmable sequencers and more. Users can either burn the preset directly to any of the pedal’s 6 toggle switch positions (and 128 MIDI accessible positions) or share the preset for other C4 owners to try.

Pricing and Availability. The “street” price of the Source Audio C4 Synth pedal is $239US. For additional information, product specifications, and a list of authorized dealers, visit

18 thoughts on “Source Audio Intros C4, A ‘Eurorack Modular Synth in a Pedal’

    1. I agree, Zymos. It’s clearly a marketing angle to use “Eurorack” to exploit the trendiness of it. The synth itself has zero to do with Eurorack (more of a mounting format), and almost nothing to do with modular synthesis.

      What it really is: A lightning-fast synth & pitch shifter in a pedal. The pitch-shifting is more intelligent than most, the synthesis is deeper than ALL synths-in-pedals. Program the synths via desktop/laptop/smart-device. Feature-packed synthesis

      What it really isn’t: Eurorack or Modular.

    1. On the unit, there a total of 128 presets. However, you can only access 6 of them directly from the unit. You have to use an external editor to access the other presets. You can connect your smart device via headphone to input 2, and use the editor that way. (it’s pretty clever.). (I’m gonna do a little “first impressions” post at the bottom of this thread.

  1. Wow. That’s a very powerful synth– especially when compared to what is currently available. The vid shows quite a few different features, like dynamic response (to cutoff), and even scale-based pitch/harmony.

    Seems like a great option for bass players.

  2. These examples all sound 100% wet. Would be interesting to hear the mix turned down a little and some dry showing through. That could give some insight into how well it’s tracking (and tuning) too.

  3. I heard some very nice examples from the bass player on the webpage. And it showed some editing details.

    There was an example of filtered white noise, but there was no mention of a noise source in the synth. Does anyone know about that?

    1. You can edit your own patches both with the desktop app, and a mobile app. They cleverly have a way you can use the audio input 2 (on the ring) as a link from the mobile app. That is outside the box thinking!

  4. I downloaded the app and put it in offline mode so I could poke around. Pretty good scale list. No noise-generator. Some noticeable limitations here & there, but all-in-all a stunning package.

    Ordered it yesterday.

  5. To me, the C4 is preferable to the Boss SY-1, as the C4 is much more tweakable, versatile, and inter-operable.

    The SY-1 is probably much more turn-key– and has more variety on tap in stand-alone mode.

    The C4 requires more interaction to get the sounds you want, but can do more with your dry signal, and has more features for customization. Seems more bass friendly, but I’m not sure.

    1. It is a great pedal but if you’re not proficient technically like me it is hard to figure out.Here’s to hoping someone puts up some videos showing how to access these functions as it’d help in conjunction with the manual.

  6. My new C4 arrived a couple days ago and I’ve tinkered with it some. Here are some first impressions.

    The build quality is great. The location of the alt button on the back is the only odd design choice and it’s fine. Having 7 realtime controls (1 exp pedal, 2 dual function knobs, and two single-function knobs) is impressive for a standard sized stomper.

    The tracking is fast, and I’d say 95% accurate. There are some cases that “confuse” the pitch tracking– like playing alternating octaves on bass. Still for pitch-to-synth, I’d say it’s comparable to the Boss GP-10 (which requires a GK/SA pickup). It’s quick enough, and fairly dynamic. It responds appropriately to soft playing, but seems to max out with louder playing. I’ve not found the sweet spot with settings to get full dynamic range.

    The Neuron editors allow you to access to all the features of the synth. The desktop version is nicer than the iOS/Android versions. They are functional, but neither are particularly “elegant”. I’d love to beta test for them and offer some suggestions for improvements. There are some aspects of the software that aren’t self-explanatory, and the manual is pretty clear but doesn’t explain everything.

    The out-of-the-box stand-alone presets mostly focus on octave-down synths. I quickly edited them to be unison- as I have a 5-string bass and don’t need the lower octave. I also closed the filters as I didn’t want the tones to be so prominent and buzzy. That process was quick & painless.

    Mixing dry with wet reveals some pitch tracking differences. At first, I thought they were “problematic” but I realize this pedal— with it’s imperfections and limitations, actually has quite a bit of personality. And the glitches are not so terrible as to take away from the funkiness and charm of it.

    I think this will do aggressive tones much more effectively than subtle musical tones, but I’m planning to do both.

    With my bass rig, I don’t use effects. I have a graphic, and now the C4. I’m hoping to gradually start integrating it into gigs in a subtle way so that it adds some definition for some things. A bit of “fretless” growl, and some filter & chorus effects.

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