Unfortunately MIDI support is broken on the RPi4 or any Pi running Buster.
It’s a long story, but essentially the Pi Foundation terminated my funding prematurely. Despite that, I still built and released version 3 of Sonic Pi for the Pi and delivered it to them for release on the Stretch version of Raspbian.
Pi Trading then released the Buster version of Raspbian and included v2.1 of Sonic Pi - effectively silently downgrading all their users to a much older version of Sonic Pi without any warning or notice on their lengthy release blog post.
When I pointed this out they initially claimed there was no downgrade?!? And then once they realised there actually was I offered to make them a new release for Buster if they could fund the development work. They declined.
Subsequently they made their own release of v3.1 and unfortunately didn’t do a good job and failed to build the MIDI / OSC support correctly. This is now shipping on their latest Raspbian and is unfortunately completely out of my control.
As the RP4 requires Buster, I can’t recommend it at all for Sonic Pi if you want to use MIDI or outgoing OSC.
The only ways forward from this that I can imagine are:
- The Pi Foundation or Trading company fund me to make a proper release
- They build it correctly themselves (or get someone else to)
- Someone does the hard work of releasing v3.1 doe Debian proper and it then makes its way int Raspbian like any other Debian package.
Sorry for the inconvenience.