So after a lot of experimenting, we finally had our first full band rehearsal over Jamulus yesterday. Which was also our first rehearsal, period, in a very long time.
It was glorious.
I ran four clients to send out separate signals from my home studio: one for my vocals, one for my guitar, one for our stereo backing tracks and one for our clicktrack. That way, everyone can mix those elements to their liking. Everything is routed internally out of Ableton Live through JackRouter to the correct Jamulus client. The other three band members (guitar, bass and drums using a digital kit) just run one client each at their respective homes, so there's seven in total.
The backing tracks are based on the extensive demos we record for each song; they contain the synths (we don't have a live synth player) but also each of our own prerecorded parts, which I can unmute to fill in for any absent members.
We've tried different locations and setups for the server. There's a public server nearby that's always on and has excellent ping and latency times, but if you're trying to have a focused rehearsal it's not ideal (though quite funny) to constantly have other musicians trying to play along. We could mute them or solo ourselves, of course, but it felt rude to do that on a public server that isn't our own. We also didn't want to depend on the availability of that server.
Running a private server on my studio computer, along with my four clients and Ableton Live, works but isn't great for latency. We tried a Raspberry Pi running the server from our drummers workplace, which has an industrial fiber connection and gave us very low latency, but we had trouble setting up port forwarding there and often couldn't reach the Raspberry Pi anymore.
Finally, we settled on running the server at our drummer's home. That way, he always gets the lowest latency, and the rest of us get around 50ms, which is absolutely fine for us. Maybe the clicktrack helps, although on one of our earlier testing sessions the drummer and I spontaneously erupted into an hour-long jazz/funk jam with me playing synths and digital piano, which proved to us that the technology is advanced enough and feels natural enough to make musical things happen (we're actually a doom metal band).
We ran a video call on our phones so we could see each other and communicate visually while playing. It felt very much like a regular rehearsal, which made us very happy. In fact, I'm pretty sure we'll continue using Jamulus even after the Covid restrictions are lifted, in addition to in-person rehearsals, because it's just so convenient to quickly work on a song without having to drive to the rehearsal space and set up. Also, the precise personal mixing and low volumes make for a very analytical monitoring experience: I could hear every note from everyone, which is not the case at regular rehearsals.
So: thank you, SonusStudios, for making me aware of Jamulus. I always assumed online jamming wasn't really there yet, but your post convinced me to give it a try and it works!