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Creating a MIDI Pass-Through Recorder

Create an inline MIDI recording with an Arduino, an SD card module, and never lose your musical noodling ever again!

Creating a MIDI pass-through recorder
If you’ve ever used audio software on the computer, you probably know that MIDI exists: a signalling protocol that allows controllers to control virtual instruments like synths. It’s also the protocol used by real audio hardware to talk to each, and you can think of it as the language in which, rathar than communicating a fluctuating voltage signal or series of discrete sample values, devices talk about what is being done on them (“A4 got pressed”, “F4 got released”, “the mod wheel moved down”, etc).

As such, there are two ways to record digital instruments (real or virtual): you can record the sound they’re making, or you can record the MIDI events that cause them to make those sounds, and that’s where things get interesting.

There are many, many ways to record audio, from microphones to line monitors to audio interfaces, on dedicated hardware, computers, phones, etc. etc., but there aren’t all that many ways to record MIDI events. Essentially: unless you’re running software that monitors MIDI events, there just isn’t really any way to record MIDI. So I set out to change that: in the same way that you can just hook up an audio field recorder (like a Tascam DR-05) to sit between an audio-out on something that generates audio and an audio-in on something that should be listening to that audio, writing that to an SD card as .wav or .mp3 or the like, I built a MIDI “field recorder” that you plug in between your MIDI-out and some MIDI-in, indiscriminately recording every MIDI event that gets sent over the wire to an SD card as a .mid file.

You’d think this would be something that already exists as a product you can just buy (even if at probably quite the markup because it’s made of “powder-coated extruded aluminium” with “audiophile quality” components, but still). Amazingly, it is not. There’s just nothing.

So: if you want a MIDI recorder, you’ll have to build one… and if you want to build one, this post might be useful to you!”

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