Platform for a Serum/Vital-like wavetable synth? MCU vs Linux/SoC

Hi!

I’m currently building a fairly ambitious wavetable synth that I eventually want to run as Eurorack hardware. I’ve been prototyping/optimising it for the Daisy Seed (STM32H750), but I’m starting to wonder whether fighting to fit everything onto a relatively constrained MCU is the right approach, or whether I should move to a more powerful platform.

The target is roughly a hardware Serum/Vital-style engine: \- 3 wavetable oscillators per voice \- 256 × 2048-sample wavetables \- up to 16-way unison \- spectral/wavetable transforms \- FM \- filters + FX \- potentially \~128 oscillator instances running in the worst case \- ideally 48 kHz with low, predictable latency

Hardware-wise I’d like: \- 8 CV inputs \- 8 DC-coupled CV outputs for oscillators/LFOs/envelopes/etc. \- stereo audio output \- =128 MB usable RAM \- small enough for a \~26 HP Eurorack module \- ideally <€50 for the compute platform/SOM

I’m particularly interested in where you would draw the line between a fast bare-metal MCU and an application processor running Linux/RT Linux or an RTOS.

A few platforms I’ve looked at:

**Daisy Seed / STM32H7 - 30e** What I’m using now. Great ecosystem for synth DIY and deterministic audio, but RAM and CPU become serious constraints for this kind of engine.

**Bela Gem Stereo - \~€78** Looks very attractive for low-latency audio. I’d still need to add the DC-coupled CV outputs, and it’s a little more expensive than I’d like.

**Bela Gem Multi - \~€183** Pretty much everything I need, but too expensive for the target BOM.

**Teensy 4.1 - \~30e** Very nice bare-metal option, but limited RAM and I’m not sure the i.MX RT1062 has enough headroom for the worst-case DSP load.

**STM32MP25x ?** This one looks particularly interesting. Cortex-A35 application cores + Cortex-M33 real-time cores could give a nice split: heavy DSP on the A cores and deterministic CV/DAC/UI/I²C/etc. on the M33. It also seems to be the direction more powerful embedded audio hardware is heading. The problem is that I haven’t found a small, inexpensive and easily obtainable SOM based on it.

**Raspberry Pi CM4 / CM5 - 50-70e** Obviously much more CPU power. I’m less sure about deterministic low-latency audio and how much work is required to make it behave like an embedded synth rather than a small computer. I also haven’t found an obvious audio + DC-coupled CV solution.

So I’m curious what people here would choose if designing this today.

Would you keep pushing an STM32H7/i.MX RT-class MCU and heavily optimise the DSP, or is this the point where moving to Cortex-A/Linux makes more sense?

Are there any affordable SOMs/platforms I’m missing, particularly something in the €30–50 range?

I’d also be very interested to hear from anyone who has built a synth around a CM4/CM5 or another Linux SOM: how good can the real-world audio latency/jitter get, and has Linux caused you problems compared with bare metal?

Thanks 🙏