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Mod Devices Mod Duo

Stompbox Plug-in Host By Paul White
Published November 2017

Mod Devices Mod Duo

Have you ever craved the ability to use software plug-ins or MaxMSP patches on stage — without the bother of a computer?

We’re spoiled for choice with plug-in instruments and effects, but there aren’t many options for using them on stage without a computer and interface. One of the handful of devices (see the Alternatives box) that makes this possible is the Mod Duo, which Mod Devices’ CEO and founder Gianfranco Ceccolini created for the best of reasons — he wanted one himself!

The Mod Duo is a little different from the longer-established Muse Research Receptor, because rather than supporting the VST or AU platforms, it runs Linux LV2 plug-ins, as well as plug-ins programmed in MaxMSP, Pure Data or Faust. The programming side of things obviously opens up a million possibilities if you’re into that kind of thing, but for those who want to plug and play, why choose LV2 rather than VST or AU? Well, LV2 is an open-source platform, and there are already many plug-ins available free of charge. At the time of writing, the manual currently lists 14 different developers who make plug-ins compatible with the Mod Duo, but this list is expected to grow, and Mod Devices tell me that a commercial store for third-party developers should be online by the time you read this review.


The Mod Duo is a stereo/dual-channel device that can accept guitar/bass, line or mic signals (it doesn’t provide phantom power, though), and which can host both effect and instrument plug-ins, including more esoteric creations such as loopers. Perhaps most intriguingly to me, as a guitarist, is that the Mod Duo can run multiple chains of plug-ins to create virtual pedalboards; as in most DAW software running on computers, the limit on how many plug-ins it can run is set by how many CPU cycles each plug-in requires.

The hardware is, in essence, a compact computer built into a die-cast aluminium stompbox enclosure. There are two quarter-inch analogue audio Ins and Outs, MIDI (DIN or USB) In and Out and USB I/O, and the analogue outs can be used balanced or unbalanced. There’s also a dedicated stereo headphone output with its own volume control and facilities for direct monitoring. The device is powered by a universal-voltage external PSU; an external battery pack is also planned.

On top of the unit are two monochrome, backlit LCD displays, two knobs and two footswitches. All the controls are assignable, and the footswitches may be used to access one plug-in at a time, to switch between saved pedalboard setups, or to change parameters such as a rotary speaker’s modulation rate. Both knobs include push-switches that provide access to and control over plug-in parameters from a familiar menu system.

For connecting a MIDI keyboard over USB, the USB Type A host port can be used; this same port may also be used to connect a Bluetooth adaptor, while attaching a USB hub allows the connection of multiple USB devices. The USB Type B connector is a slave port used for connecting to a computer, editing and running firmware updates. We’re also told that the hardware itself adheres to a modular design so as to make future upgrades easier.

Just Browsing...

As supplied, the Mod Duo is pre-loaded with a number of pedalboard setups. You can edit the individual plug-ins directly from the front panel, but for more serious editing or for creating new pedalboards from scratch, you can connect it to a computer and edit everything from your web browser; the manual tells you the URL to enter, and when you’ve done that, the graphical editing window appears on your screen. The editor’s being browser-based means no additional software is needed.

The browser-based pedalboard creation process follows the kind of drag-and-drop approach many of us have become accustomed to in the likes of Line 6’s modelling software. Plug-in Modules already loaded onto the machine are shown along the bottom of the screen, and once the Modules are on your pedalboard, cables can be dragged from the output of one device to the input of another. CPU and RAM usage indicators warn you if you’re attempting to run too many plug-ins, though in most cases I found I could deploy a very generous number of Modules before I got into trouble. When the effects are not in use, the bypass system provides the option of using relays to provide true-bypass operation, the down side of this being that you lose reverb and delay tails when you enter bypass mode.

Configuring a  pedalboard in the browser-based editor.Configuring a pedalboard in the browser-based editor.You can load more plug-ins from the online store: the initial content, comprising almost 200 plug-ins, is all free to download, though as I mentioned, it will be possible for third-party developers to offer plug-ins for sale. Existing plug-ins include variations on all the familiar delay, distortion, dynamics, filter, modulator, amp/cab simulator, spatial enhancer, pitch and looper categories, as well as ‘sound generators’ — which means software instruments to you and me. Users can also share their pedalboard setups online, which is always a nice idea.

Instrument plug-ins can be played through the MIDI input, and their outputs can then be processed with further effects. A few such instruments are loaded on the unit as shipped, and these are mainly SoundFont sample players. In my initial tests, using an Edirol MIDI keyboard, I found the MIDI instruments a little too prone to stuck notes, but I was told that this is a known issue with some plug-ins and should be resolved by the time you read this.

Because this is a dual-channel device, it’s possible to run two independent mono signal paths, so you could, for example, run an instrument in one channel and a chain of guitar effects in the other if you wished. The two channels may also be used to set up independent processing chains, a single stereo processing chain, a mono-in/stereo-out processing chain or even stereo-in/mono-out.

Hardware Control

The two knobs and two footswitches are described in the manual as ‘actuators’; the two knobs and their integral push switches are normally used to navigate the menus and activate the tuner, which is displayed in the right-hand screen. The device menu can be reached by holding down the left knob for longer than a second. To enhance real-time control, both the knobs and the switches can be mapped to one or more plug-in parameters from the Plug-in Configuration screen, which is also where the various plug-in parameters can be adjusted. Each footswitch has its own status LED, which also doubles as a level meter: the light goes out if the input level is below -30dB, illuminates green from -30 to -12 dB and yellow from -12 to -3 dB; above that, a red light indicates that clipping is imminent. Navigation is accomplished by rotating the left knob until the desired section is highlighted, whereupon pressing the knob takes you to the next level of editing. Holding down the right knob for one second puts the Mod Duo into tuner mode.

The USB Type A port allows a  controller keyboard or other MIDI device to be connected, while the Type B port caters for connection to a  computer.The USB Type A port allows a controller keyboard or other MIDI device to be connected, while the Type B port caters for connection to a computer.Menu browsing through the monochrome LCDs can make you feel rather as though you’ve been transported back to the late ’80s, but the web editor looks instantly familiar and very up to date, with nicely rendered graphics. The bar at the bottom of the web interface allows you to navigate the key sections of the interface: there are a pedalboard builder, a pedalboard library, banks and the plug-in store. You can also bypass the individual effects chains from there, as well as monitor CPU and RAM usage.

Making Connections

When you come to connect up the various plug-ins, there are three types of virtual cable: purple for audio, blue for MIDI and orange for Control Voltages. Connections are dragged as required but can’t be connected to the wrong type of socket: you can’t put an audio jack into a MIDI input by mistake, as it won’t let you. To remove a connection you just unplug it from the receiving end. The clever bit is that you can take multiple cables to a single input to mix them, or split an output to any number of destinations. This enables some pretty ‘out there’ configurations to be created with ease.

The free plug-ins include TinyGain, which allows you to change the level of an audio stream and includes a basic audio meter, making it easy to check that the digital audio signal is getting to where it should. Currently there’s no MIDI equivalent but Gianfranco thought my suggestion to add a simple MIDI activity monitor was a good idea, so hopefully we’ll see that soon.

The Plug-in Configuration screen is accessed by clicking the gearwheel icon at the top of the desired plug-in screen. This brings up a full set of parameter controls, and allows you to map plug-in parameters to the knobs and switches of the device using the fader icon next to each parameter, which brings up a menu of options. The range of control can also be set here. A MIDI Learn facility helps when mapping parameters to an external MIDI controller; when MIDI Learn is selected, you just need to send the desired command from your MIDI device. Once a parameter has been mapped, though, it can no longer be adjusted from the interface, only by the designated control or MIDI message.

Mod Devices Mod DuoMultiple pedalboards can be saved in the Pedalboard Library, in which clicking on a pedalboard makes it active. To cycle through the pedalboards in the current bank you can set the two footswitches to move up and down through the pedalboards, or you can send MIDI Program Change messages from an external device. It’s also possible to save multiple presets for the same pedalboard, with different control settings or with different plug-ins bypassed.


The memory is organised into banks. You can create a new bank whenever you need one, choose the method of navigating through its contents (this can be different for each bank if you wish), then add the pedalboards you want to be included by dragging them in. Finally, just place them in an order that makes sense to you. The Banks section displays any banks you’ve created using the web interface as well as an All bank that contains your pedalboards. By navigating to a bank and clicking on the left button, you can browse the pedalboards in that bank, and you’ll see an overview of what’s in each pedalboard. Navigate to the pedalboard of your choice and click the left button to load that pedalboard, and to make the bank the currently active bank. As all the Mod Duo’s controls are assignable, using a separate MIDI controller for navigating banks and pedalboards could make life very easy.

Feel The Quality

The existing range includes multiple flavours of chorus, flanger, delay, reverb (including the now obligatory Shimmer Reverb) and so on, but you’ll also find a number of software instruments and a couple of Leslie emulations, and the amp and speaker emulators worked pretty well for me. Knitting all this together in the editor reminds me somewhat of NI’s Guitar Rig software; you can come up with some really fun creative ‘tangles’. Overall the quality of the plug-ins is generally very good: they compare well with equivalent VST/AU offerings.

Mod Devices Mod DuoThe Mod Duo’s simple MIDI mapping also works well, and for things like the Leslie emulator, you can easily map the speed change to one of the footswitches. Having some software instruments on board is useful, and feeding them through a complex serial/parallel web of virtual pedals is easy. The LV2 instruments presently on offer may be relatively simple, but they sound pretty polished to me, and no doubt more sophisticated options will soon follow.

Final Impressions

If you like the idea of a stereo plug-in platform that can be loaded with an ever-expanding range of open-standard plug-ins, which has the flexibility to be used as a dual-mono processor, and can even be loaded with software instruments... then the Mod Duo is definitely worth a closer look. Although you need access to a computer to get the best out of it, its browser-based editor means you’re not tied to a specific machine or software package. (It might be an idea to use a label printer to write the URL on the bottom of the box!)

Where live performance is your priority, I’d recommend using a MIDI floor controller, as this will give you access to switching pedalboards and banks, leaving the switches on the unit itself free to control other functions. But in the studio I don’t think it’s required — that lovely browser interface makes creating new sounds very easy. It’s already a very usable platform, but it’s also brimming over with potential, and I’ll be very interested to see what new creations are made available for it in the months and years to come.


Muse Research’s Receptor and Musebox and Seelake’s AudioStation X64 can run the same VST plug-ins most DAW software uses, but they’re bigger and pricier options. The Rebel Technology Owl range comprises Eurorack and pedal versions, which are more comparable to the Mod Duo —they can run MaxMSP Max Gen patches, as well as bespoke creations programmed in PureData, Faust and C++.

Maxing Out!

MaxMSP support was included from the outset, but an update in August 2017 streamlined the integration process. No doubt this will pique the interest of Max users, and the Max For Live community too. Direct use of Max For Live patches is not possible straight away, but Mod Devices allow the use of patches based on Max Gen modules, and lots of Max For Live patches are already Gen-based; the patcher needs only to use the ‘MOD Duo Watcher’. Encouragingly, a community of Max For Mod Duo users seems to be growing. You can find out more details on Cycling74’s web site.


  • Hardware runs open-source Linux LV2 plug-ins, many of which are free.
  • Generally high standard of LV2 plug-ins.
  • Supports MaxMSP and some other programming languages.
  • Can host instruments as well as effects.
  • Excellent browser-based user interface.


  • Requires a separate controller to make the most of it when playing live.
  • Doesn’t support AU/VST plug-ins.


As a compact platform for running and routing multiple effect, emulation and virtual instrument plug-ins, the Mod Duo has a lot going for it.


€649 including VAT.

Mod Devices +49 (0)30 555 70 435

€549 (about $645 when going to press).

Mod Devices +49 (0)30 555 70 435.