harmoxen VS ptcollab

Now for your first question, I don't know about doing it with arduino, but if you manage to find resources to send simple midi messages, it'll be the same thing to send MPE messages as well. As to what messages you should actually send however, I used this to understand how to send pitch bend range information, and learned the rest from the spec and a bit of tinkering. You can check out the source code of my custom piano roll which uses MPE to send notes with arbitrary frequencies. The relevant parts are the setup_mpe method, which just has to run once in the beginning to setup the synth to which you're connected. The other ones are note_on and note_off. (sidenote: actually here I'm not using the least recent channel because I was lazy when I wrote this, but)

Cave Story OST is not made with PxTone, but with OrgMaker. But, there's a fork of PxTone called ptcollab that was recently updated to be MIDI kryboard compatible. And yes, the original PxTone Collage can read thr files made with ptcollab. Ptcollab is a much better experience overall.

ptcollab (pxtone collab) is a music editor where you can collaborate with friends.[0]

[0] https://yuxshao.github.io/ptcollab/

This is super exciting! I've been exploring this space of collaborative music editing too (and will shameless plug a multiplayer piano roll DAW I worked on [1]) and had some thoughts.

1. When collabing with friends it was slow for us to iterate because we (and a lot of people) just send files back and forth. It was hard to sketch things out without having some other kind of whiteboard. Of course others who can communicate musical ideas better through words probably would handle this a lot better.

2. Multiplayer editing was really fun in comparison. The magical moment is when you're working on some section and you listen to the song again and you realize someone else has added something on top of what you were doing earlier. It's like the song has taken on a life of its own.

3. Even with multiplayer it's still hard to coordinate and you can't get around planning even with rich tools. If the song was gonna be serious and not just doodles, we usually had to voice-chat to discuss what'll go in each section, then sorta divvy up parts. I guess the upshot is that even with the ability to be 'maximally' present with others, many people, myself included, work best with some amount of private creative freedom.

When I jammed in a bigger group, flows like relays or Monsquaz swap [2] that gave people that freedom, then at specific moments let them intermingle, seemed to work best for getting something out at the end. (If it was a free-for-all people usually ended up doing their own thing in some measures they staked for themselves out in the roll. Or otherwise people just spammed meme songs like Megalovania everywhere.)

[1] https://github.com/yuxshao/ptcollab