[sdiy] LocalDSP and Jazzman

Fri Jan 16 05:45:44 CET 2026

Fantastic video and really cool project, Chris. The demo sounds great, I'm
looking forward to playing with the app.

Nathan

On Thu, Jan 15, 2026 at 9:36 PM Chris McDowell via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Howdy list,
>
> I wanted to share a fun project I've been working on for a good while.
>
> [image: hqdefault.jpg]
>
> Jazzman: a 3-operator FM Synthesizer
> <https://www.youtube.com/watch?v=8D7tZ3UgT8Q>
> youtube.com <https://www.youtube.com/watch?v=8D7tZ3UgT8Q>
> <https://www.youtube.com/watch?v=8D7tZ3UgT8Q>
>
> Backstory: when I was running Super, I had one particularly stressful
> holiday season. My wife urged me to stop thinking about synths entirely and
> just give myself permission to chill and "follow my nose" for a few weeks.
> This pretty quickly led to me falling into a crazy rabbit hole of designing
> a hardware FM synth... 2OPFM was my most popular module and I had gotten so
> familiar with the tones it had it offer. I wanted to build a polyphonic
> version with some more tame-able controls, so I wired up MIDI to the back
> of a module and got to it. I was able to get 12 voices and chorus working
> on an STM32F334 which felt like quite the achievement. I dubbed it
> "Jazzman", fully knowing Crumar made a jazzman and that I should change the
> name or it would stick in my heart and I wouldn't be able to really change
> it later. I designed a bent metal case, had it made, put it all together,
> played a few shows with it, then sat on it. I got re-occupied with Super
> and life, and sort of shelved the project.
>
>
> Fast forward to early fall 2025. I never renamed it, it's just so Jazzman,
> and the concept had stuck around. Jazzman was now more of an ethos than one
> product: FM is sick, it's NOT hard to program like legend has it, and it
> suffers from too many parameters and stupid little screens. Jazzman is one
> possible answer to all that: an immediate Juno-like interface and a
> stripped down architecture to support a wide spectrum of tasty FM stuff
> without being completely off the wall complicated. Around this time, two
> things happened. 1: I had mental shift away from "I'm building a synth on
> this chip, let's see what fits" and toward "I'm designing this synth, let's
> see what chip can handle it", and 2: a friend introduced me to someone who
> wanted help designing -their- synth. Anyone who has done any
> microcontroller work knows that the development process pretty much sucks.
> I would always find myself accidentally fighting against hardware or
> platform bugs when I was trying to focus on pure sound, and the cycle of
> tweak-flash-tweak-flash was super tedious. As I wanted this
> synth-dev-for-hire experience to NOT suck, I resolved to build a tool I had
> been dreaming about for years: LocalDSP.
>
>
> I'm not really a computer guy. I mean I hella use my computer, but I am a
> microcontroller developer and not a "software developer". Certainly not a
> webdev or Electron or big GUI desktop sort of developer. While I know this
> is old news to some, I was EXTREMELY stoked on the possibility of
> developing my DSP on my macbook totally separate from the hardware for
> faster iteration and testing. With Claude holding my hand, I started
> developing a framework / build system for writing the DSP in one place in a
> totally platform agnostic way, with an explicit contract for communication
> outside of the DSP core. I had prototyped the "work synth" in MaxMSP with
> most functions in gen~ knowing they'd eventually become C on a
> microcontroller, so I started with porting that guy (codenamed "paul") to
> the fledgling environment creatively named LocalDSP. It worked, it was
> sick, and I immediately realized I needed to build the next-generation
> Jazzman here.
>
>
> I had a thought that it should probably deploy to VSTs, too, for lots of
> reasons but the main one being easy sharing with my clients and buddies.
> Some early specific technology friction with the paul client got me
> thinking it would be sick for it to deploy to the web in a really smooth
> way so I could just send a link to the latest build and we could all play
> around on our phones. This became QUITE the rabbit hole, but I eventually
> got LocalDSP set up to build the C DSP core code into WASM and stick it all
> in a website. Because of the way LocalDSP handles parameter definitions
> (which is its own long story), it is really easy to parse information about
> them with python or javascript. The WASM builds take all that info and
> create UI controls for them so I don't have to actually write javascript or
> do much manual work when deploying any of the projects to web. I have to do
> a bit of fiddling when creating a new "skin", but once it is set up the
> metadata from the parameters defines where in the UI they'll go, and the
> skin code defines how they'll look. I went a lil' silly and used threejs to
> build a 3D interface for my main skin, and I'm really quite happy with it
> even though the floating labels kind of stink!
>
>
> Somewhere in the middle of all this, I got to work on the Jazzman
> hardware. I had recently done a work project on an STM32H750 and was
> hankering to put it work for audio, so I built a "synth dev platform" PCB
> based around one with USB, MIDI, audio outputs, and a ton of headers for
> ADC inputs. Not a great approach for a product but I wanted these boards to
> be flexible enough for a few different projects I had in mind. Once I got
> the PCBs back, it was time to implement LocalDSP's tastiest trick: plop all
> that same DSP code into a STM32 platform template such that "make deploy
> jazzman" in my terminal would build and run the synth on my laptop, trigger
> the WASM build, deploy to my site, AND perfectly update the STM32 project.
> I am proud to say it all works. Jazzman is "platform agnostic" and runs
> everywhere I want it to.
>
>
> I could not have done this in any reasonable amount of time 5 years ago,
> the future is crazy. This video is just a little intro, feel free to play
> around at https://jazzman.vercel.app/. Along with this system, I've put
> together a way to turn any .glb / .gltf scene into an webmidi controller,
> mapping CC output and animations via object naming... more to come on that
> one 😜
>
>
> Cheers,
>
> Chris McDowell
>
>
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