[sdiy] LocalDSP and Jazzman

Fri Jan 16 13:54:55 CET 2026

Thanks, Nathan! 

And Richie, yep this hardware has a pin dedicated to that and I'm at about 20%.

Plennnty of room for verb, delay, and a few more voices 👹 I'm swimming in ram on this chip, too, it would be criminal -not- to. The H750 is beefy. 

Cheers,
Chris McDowell

> On Jan 16, 2026, at 3:55 AM, rburnett at richieburnett.co.uk wrote:
> 
> Cool story and some cool FM sounds there too!
> 
> Do you have an idea of how much percent of the STM32H750's available CPU cycles the current firmware is taking to run?  I'm just curious ;-)  Maybe there's enough left for Reverb and/or Delay FX too!?
> 
> -Richie,
> 
> 
> 
>> On 2026-01-16 04:45, Nathan wrote:
>> 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.
>>> Jazzman: a 3-operator FM Synthesizer [1]
>>> youtube.com [1]
>>> 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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>> Links:
>> ------
>> [1] https://www.youtube.com/watch?v=8D7tZ3UgT8Q
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