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Other companies consider development kits as a revenue stream (I've used dev boards in the past which cost over $1000, plus licence fee for the software that goes with it) but ST has taken the opposite approach: they subsidise the dev boards! A development board for the STM32L476RG costs only a few pennies more than the bare chip on its own. They are actually the main reason that ST is one of my favourite companies. I also used a dev board – the nucleo boards from ST are fantastic. This served as the prototype hardware for a while, and the basic synth was developed on it. You can select which peripherals are in use and set the master clock speed, and see what the resulting amperage would be.Ĭonvinced that this was going to work, I set about writing a basic synthesizer and powering it from MIDI.Īs evident in the picture, the sound output was only mono at this point and my confusion over the behaviour of ceramic capacitors led to me sticking a bunch of them together in an attempt to get the needed capacitance on board. I really don't like it as a replacement for the older style peripheral libraries and example projects, but the power consumption calculator is exactly what we needed. Rather than peering through datasheets, I used the STM32CubeMX software. You can reduce this by disabling output buffering, but then the signal would be too weak for our use. There is also a fixed additional power consumption for any peripherals you enable. The datasheet gives a power consumption in terms of μA per MHz. Pretty astonishing what that chip can do, it's a super duper micro. This has 1MB of flash memory, a built in DAC, everything we need. I next made a search for a more appropriate chip, and given the specification initially settled on the STM32L476RG. But when powered by MIDI, there was no hope here. The header on the right is a standard ST-Link connection, and it worked fine when powered from there. This was a functioning synthesizer, that produced some basic square waves when MIDI arrived. Since there was no harm in trying, I threw an STM32F103 onto a board to see if we could power it with the midi signal. This synth needs to produce a repertoire of sounds big enough to silence such comments.Īs I concluded with my last attempt at a polyphonic synth cable, the solution is to throw more processing power at it. Some people criticised my original Smallest MIDI Synth for only producing a square wave with no envelopes or filters.

Produces as many 'bleeps and bloops' as possible.

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This means stereo and full audio bandwidth: I aimed for the standard samplerate of 44.1kHz. Pulling its power parasitically from the plug. The synth is designed to work perfectly with the Tonal Plexus – Aaron's microtonal MIDI keyboard, which sends a pitchbend range of 1 semitone, to get the most accurate detuning of notes. This means respecting the full 14-bit value (something most keyboards don't even send) and also working with the RPN pitchbend range adjustment messages. More complex patches could also be added at a reduced polyphony, but the main algorithms are aiming for 16. Fully polyphonic, meaning 16 voices for the standard patches.

The first thing we did was decide on what the synth should do: There is a transcript of the technical explanations at the end of this page.

The first half of the video is a demonstration of the synth, with the rest being a technical explanation. A production run is under way and the finished units will be sold on his site, H-Pi Instruments.

This project was built as a commission for Aaron Andrew Hunt. A tiny, powered-by-MIDI, polyphonic FM synthesizer that supports full resolution pitchbend and microtonal tunings.