ALM/Busy Circuits founder and developer Matthew Allum is indeed, well, busy. This year we saw a number of new ALM devices top our year-end charts, celebrated the release of the stylish and ultra-jammable Turismo system, and even welcomed a handful of VST effects, synths, sequencers, and VCVRack adaptations. Matthew and the rest of the ALM team's busy efforts continue to inspire our own patching practices, cooking up modular bliss with reimagined classics, bespoke designs, and a careful attention to accessibility and user experience.
Today we get the pleasure of introducing another new addition to ALM's fantastically capable catalog, the MCO MkII. Inheriting aspects of the original MCO's unique wavetable design, now supercharged with additional processing power, MCO MkII goes far beyond the original oscillator with multiple voice modes, onboard modulation, filters, and envelopes, all in just 6HP. Despite its comparative depth, using the module is simple and intuitive, incorporating aspects of the Pam's Pro and MFX workflow with a full-color, animated screen interface.
Having had some time to patch with MCO MkII, exploring its many paths towards captivating sounds, it's safe to say this module will be an exciting newcomer for many in the Eurorack world. Its flexible synth and effect engines, compact size, and convenient preset system make it ideal for streamlined performance cases, while its sheer breadth of capabilities will undoubtedly offer new modes of creative signal mangling to studio practices.
Between sessions of wavetable wonderment and vocoder-crazed fugue states, we were lucky to carve out some time to speak to Matthew about MCO's impressive successor. In our conversation, we explore MCO MkII's origin story, dive under the hood for a few of its voice modes, and explore some of the inspirations behind ALM's characterful and feature rich designs. Read the full interview below!

An Interview with Matthew Allum of ALM/Busy Circuits
Perfect Circuit: Hello, Matthew! Thanks for taking the time with us to talk through MCO MkII. The original MCO was comparatively streamlined, offering a unique wavetable architecture without digital menus, giving users a conventional path towards exploring MCO's unique sounds. What led you towards implementing the multi-algorithm approach for MCO's successor?
Matthew Allum: The original MCO is nearly 10 years old and though a cool little oscillator it had definitely begun to show its age in today's Eurorack world. Late 2022 we had the opportunity to start working with a new, then in development processor chip. One of the projects we started to stress test the new chip was ‘What if the MFX was an Oscillator’. We were very happy with the results and with the dual core nature of the chip it meant we could be a lot richer with the UI and it did not affect audio processing (which was also very capable- chords etc). It initially wasn’t actually called the MCO but then it dawned on us that it was really the MCO evolved so it became the mk II.
The wavetables and synth engine with sub etc from the original MCO lives on in the mark II just greatly improved with many more wavetable parameters and the ability to copy in your own wavetables via USB.

PC: MCO MkII continues ALM's knack for delivering the nostalgic sounds of varied digital synthesis methods inspired by classic gear, bringing those nostalgic sounds to the modular environment for further expansion. How did ALM carve out this niche, and what inspires you about classic digital synths like the DX7, CZ-101, JP8000, SID chip, etc?
MA: It's just what I ‘grew up’ with and what is familiar to me as well as from a technical perspective being interested in how technical limitations were worked around and how that generally gives the technology its sound (which may well have been seen as a downside at the time). I like the idea of bringing such technologies into a new context so they can be experienced again but controlled and interacted with in a totally new way. It's also fun to add our own spin or kind of alternate future/history for the technology.
PC: Virtual Analog sounds are the focus of the Virtana mode in MCO MkII, a comprehensive voice with resonant low pass filter and even a drift control for a realistic vintage instability. Given that virtual analogs vary in their often jam-packed featuresets, I'm curious how you narrowed down this voice to what we get in MCO MkII. Were there particular instruments inspiring your design?
MA: The focus of the Virtana is really on the kind of very early ‘Virtual Analogue’ synths such as what Clavia were doing with the Nords etc and sound really is in its infancy but not without a lot of charm. I guess the feature set was limited too which was an influence on the parameter but also maybe wanting something SEM like where maybe just a few but well selected features can get you very far sound wise and not be too overwhelming.
PC: In MCO MkII we also get the return of your Commodore 64 synth chip emulation, which you've explored before in your now discontinued SID Guts and SID Guts Deluxe modules. How did you approach porting this character-rich engine to the MCO MkII, and were there any changes from your earlier implementations?
MA: The SID GUTS module used an actual SID chip to produce sound and the MCO basically approximates it through rough emulation. I wouldn’t make any claims to how deep we’ve gone with that emulation but it definitely sounds close enough to me and has all the features there. It's one of my favorite oscillators we’ve done and it was a shame to discontinue the module so I was really chuffed when we realised we could rebirth it in the MCO.
PC: Let's talk vocoders. The Sylon voice mode in MCO MkII offers both classic vocoding and an FFT-based spectral resynthesis engine, and I quickly lost track of time having fun running drum loops and speech samples into both of these potent processors. Were there particular pieces of gear that inspired you to include a vocoder in the module?

MA: I’ve always been fascinated with vocoders especially running things like drums or acid lines through them. I'm fortunate to have a Roland SVC 350 which I love but am also a big fan of the AnalogFX VXC-2220 Eurorack Vocoder and the big Frap Tools FUMANA. Unlike these the MCO implementation is of course fully digital but I think it sounds great, saves quite a bit of space comparatively and has some fun options you couldn’t really do in the analogue domain.
PC: The FFT-based engine isn't one I generally associate with the sounds of the 90s/00s outside of academic computer music circles, and I've primarily only seen hardware FFT-based designs in recent years as processing power shrinks in physical size and cost. Is this sort of computer music something that inspires your designs, and how did you arrive at the FFT mode in Sylon?
MA: Companies like Alesis with the ModFX series were doing great digital vocoder implementations around the early 2000s which I assume would have been FFT based but with custom silicon. ModFX units still sound great and all have a distinctive character. But as much as this influenced us, doing something FFT based was really a chance to stress test the chip as mentioned previously and our coding abilities. We also thought a vocoder would be a nice addition as it's both a vco/voice and an effect and could take advantage of the extra audio rate input we have on the MCO.
PC: Like the ALM MFX and Pam's Pro Workout, MCO MkII features ALM's single encoder and button navigation workflow. Like the other modules, I was surprised at how intuitively I found a feel for when to long press or short press, making quick work of setting up a complicated CV and voice parameter set-up. Were there any particular challenges to implementing this workflow for MCO MkII's many settings?
MA: We followed the now familiar model we’ve used on the modules you mentioned but wanted to take it further - much more visual feedback (through animation etc), new global and stacked parameters to simplify complex parameter and speed access, jack detection and new shortcuts for power users - such as the quick modulation assignment.
I also think it's a kind of less is more approach where we are continually dog fooding and adding stuff as much as we are taking away to keep the UI simple and easy to use. But also not getting too bogged down in rules… having fun with it too and giving the device some soul and character.
PC: When exploring the MCO MkII, I skiffed together a system with Pam's, Squid, MCO MkII, and MFX, which in addition to being an incredibly fun and capable minisystem, really showed off the progress ALM has made with visual user interfaces. MCO MkII's screen animations and UI are in full color, and I found simple visual metaphors like relating the closing of a low pass filter to rounding the edges of a square both effective and pleasant. What inspired the upgrade to this screen interface compared to earlier ALM models, and how did you go about developing its visual language?
MA: Thank you! It was a real team effort here and I’ve got to say we all contributed with a lot of fun back and forth, experimentation and really organic growth of its visual style and language. Lucas here did an incredible job with all the animations (as well as the bulk of the DSP!). The inspiration really was the challenge of wanting to build on previous efforts and further what was possible (and what the hardware allowed).
PC: MCO MkII features the ability to save user presets in each voice mode, which considering the configurable nature of the device, will undoubtedly be a useful function for musicians to recall their favorite sounds and set ups. Likewise, the factory presets provide a great place to get started in each mode. How did you and your team approach designing and narrowing down the factory presets included for each voice?
MA: The presets were done by the amazingly talented Zoey here who really is one of the most skilled musicians & synthesists I’ve ever been fortunate enough to meet.. We wanted to have presets that were relevant, useful and showed off what the MCO can do but also be educational in acting as good starting points in building your own sounds. Hopefully we achieved this. All the presets are listed and described in the manual.
PC: In recent years, the modular world has seen more and more sound generators with integrated functions like envelopes and output level VCAs. The level VCA inputs on a number of ALM oscillators fit into this category, and MCO MkII is another such module, going even further with envelopes, filters, LFOs, and multiple voice modes in just 6HP. What is your perspective on this trend of consolidating elements that would typically be achieved with multiple modules, and what do you feel it brings to the musicians using your tools?
MA: I think it's all about choice, balance and compromises as well as using new available technologies appropriately and pushing the format forward.
I love the idea of portable feature packed systems especially for live performance - of which the MCO fits well into and was part of its motivation for its existence going back to the original MCO. I think we’ve done a pretty good job of making a large amount of functionality still usable in a small space but I wouldn’t argue that it wouldn’t be more usable and patchable in 52hp of space - but it’d also be a lot less accessible to most people (price & size). We like to do both too - compare the MCO to the Castle or even the Cizzle… and something in the pipeline which goes completely in the opposite 52hp direction.
I want Eurorack to be more accessible to the 18 year old me - whether this be through VCV or things like the MCO which give you a hell of a lot of bang for your buck and don't demand a lot of valuable rack space.
PC: Each of MCO MkII's voices is capable of producing up to four-voice chords, with both factory and user chords that can be modulated by one of the three CV inputs. We see a similar chord feature on a number of other modules in ALM's line up like CIZZLE and Akemie's Castle, offering a relatively unique approach to creating polyphony in the modular environment. Can you share any fun patch tips you've found with this feature of MCO MkII?
MA: I will just say Vocoder chords :) and chorded bass drums can actually sound pretty nice. Super Saw chords via the BC8000 engine are a lot of fun.
PC: MCO MkII features a USB port for simple firmware updates. While the module is already quite feature-packed, do you expect to add new voice types or other features in the future?
MA: Yes definitely! Right now we are in feature freeze mode as we get the firmware solid for release. In parallel we already have a feature update in the works planned for release January-ish and like with updates to other modules we definitely hope to continue this.