Hopping into this thread since I’m also working on the mapping for the SB3, hope that’s ok! I’m not new to software, but I am new to Mixxx mappings and DJing.
What I’ve observed: the mapping is very similar to the SB2 mapping that already exists. To get started, I just copied the SB2.js and .xml files from Mixxx into my local settings /Controllers/ folder, renamed to SB2, and find-and-replaced SB2->SB3. That got a LOT of things working! Things that definitely don’t work:
- Deck 3/4, which I guess posters up-thread are correct about re: “need to echo back the noteon from the deck button over MIDI OUT.”
- Slip on either deck (seems like it SHOULD work as far as the XML is concerned, but… doesn’t?)
- The shift states on the FX1/FX1 “1,2,3” buttons, which look like they should influence looping? But even when I press them, they just toggle the fx units?
- The transport controls below the pads (back-to-start, rewind, ffwd)
- The autoloop/ in/out buttons (looks like on SB2, these were on the hotpads; SB2 has “AUTOLOOP” and “1/2” / “2x” buttons?
It’s possible that some of this stuff works, but I don’t know Mixxx well enough to use it? It’s also possible I’m missing stuff since, as I said, I’m new here and on some level just satisfied that I can make cool vinyl scratching noises! 
Any thoughts on how to attack this? I’m happy to hack on it but I’ve got a bit of a chicken/egg problem since I also mostly don’t know what it’s SUPPOSED to do. I feel like if I had one good example I could probably duplicate it to fix a bunch of these but I’m missing a big picture on how the Pioneer business works…
[Edit]: Attaching progress so far. This is 100% derived from the SB2 mapping, so … no intention to rip anyone off or claim anyone else’s work as mine, just sharing so that other people don’t have to manually make the edits I describe to catch up with where I’m at.[/edit]
Pioneer-DDJ-SB3-scripts.js (44.6 KB)
Pioneer-DDJ-SB3-scripts.js (44.6 KB)