This is @robin.newman 's article on Sonic PI and the pisound card. Thank you Robin. This link does appear buried in another thread, but I thought it useful to elevate it to a topic. Useful for me, certainly.
I add that on mine, RPi 4 rather than 3, with the current patchbox OS, I also have to use QJackCtl to connect SuperCollider’s outputs to the system inputs. In the article, these were already connected. But they might be in future, as the SPi startup script evolves. Thing is, if not, you can these kind of things with QJackCtl.
I was connecting to my Rpi via Remote Desktop (xrdp server on the Rpi, Windows Remote Desktop on the client) and this half-broke the audio in strange ways. So don’t do that, use VNC.
This is a very old article now, so not sure how relevant all of it is. In particular linking in QjackCtl will have changed with latest SP. I am still working on this (finalising default settings for linux builds of SP). and I think I may tweak the existing links to jack in 3.3.1 as well.
It’s may be not right up to date, but the priniciples are very helpful. Not just for pisound but for linux sound in general. Certainly material for tweaking when things aren’t quite right.