STM32F746g Discovery SF2 MIDI synth

Description

I really like the Dream MIDI synth chips product line http://dream.fr/, it is a good solution to provide easy synthesizer capabilities to a project. If you don't want to customize soundsets, the SAM2695 is perfect, just solder and play. Otherwise, there is chip like SAM2655 (see http://www.serdashop.com/DreamblasterX1) with which you can theoricaly add your own soundsets. Unfortunately, Dream seems very secretive about his technology, and it seems to be very difficult to customize anything without signing NDA and paying expensive dev board.

I wanted to try the faisability of a complete customizable open source solution, and the new STM32F7 Cortex-M7 has some DSP capabilities. So here we are. I choosed Fluidsynth synthesizer http://www.fluidsynth.org/ and stripped it to be able to use it on microcontroller.

Details

I decided to split firmware to be able to eventually reuse the light fluidsynth. I think it should works on any Cortex-M4 with external memory (STM32F469 Discovery kit maybe ?).

Fluidsynth should works fine with 64 voices polyphony. I successfully tested Timidity soundfont and Merlin soundfont, but FluidR3 GM seems to fail. Note there is no reverb and no chorus effect yet. Fluidsynth original IIR filter as been removed too.

Firmware is highly inspired by ST examples, 32 bits sample are used instead of 16 bits available in the original STM32Cube examples. I also created an USB MIDI device class since there is no such class in STM32Cube.

Both software are available on github (see project links).

Next step would be maybe to design a custom board (STM32F7 + SDRAM + CODEC + SD card slot). Firmware improvement includes adding more filter and effects, and fixing some glitches. SD card reading seems to be a bottleneck with large soundfont and complex MIDI.

Discussions

John Kinkennon wrote 01/04/2022 at 18:02

I joined hackaday just now due to my interest in this project. I am migrating MIDI Encoder applications to the STM32H755 from Arduino and PIC32MZ versions. The USB MIDI Device class would be extremely helpful as that is proving to be quite a challenge. For now I have some code at www.kinkennon.com but need to update my site and move my projects to github.

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Flemming wrote 06/03/2017 at 16:40

Thanks for the idea of using STM32F7 for the MIDI synthesizer. I've tried to test your project. It seems that ST has released an update which gives lots of errors during compiling. Even the fluidsynth file causes error. Do you have plane of update your project? and do you have a youtube video for demo?

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Yale wrote 03/14/2017 at 05:59

This would be perfect for adding a built in synthesizer and speakers to my MIDI keyboard. I think it would be better to port FluidSynth (or even Timidity++) to run with only the on chip RAM and stream all samples from the SD card, so that a compact board with amplifiers can be built. This guy has done it with his Wav Trigger http://robertsonics.com/microsd-cards-for-audio/.

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STM32F746g Discovery SF2 MIDI synth

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STM32F746g Discovery SF2 MIDI synth

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