This might not be my whole config. I actually had to hack my way into this SD card as I had forgotten my password… it’s been a while so going from memory on what I touched.
After your Pi is “working” with Roon you need to get the snd-aloop module loaded. This is an ALSA module. Make sure your distribution uses ALSA.
This will create loopback “hardware” devices like:
card 0: Loopback [Loopback], device 0: Loopback PCM [Loopback PCM]
“Loopback PCM” will show-up as a RAAT destination you need to enable in Roon. There might be more than one. Enable this in Roon
Then you need to run something like:
/usr/bin/alsaloop -d -C "hw:Loopback,0,0" -P "btaudio" -l 20000 -b 8000
-d runs alsaloop as a daemon
-C is the capture device, this is where Roon is sending the audio
-P is the “Playback” device. This is probably your VU meter.
*Note, I have a whole other set of things that runs and automatically tries to attach to a specific BT speaker address in the background. That speaker is built as “btaudio” in the alsa.conf
-l is latency
-b is non-block mode and I forget why I set this
I found the Pi was dropping a lot of frames trying to feed the outbound audio device until I set the latency properly. Just trial and error. There are lots of other options:
http://manpages.ubuntu.com/manpages/bionic/man1/alsaloop.1.html
I’ll leave the rest up to you. This, hopefully obviously, is not a complete guide. If you ask questions maybe I’ll remember what else I did to make this work. Good luck. I do remember it took me a while to get the snd-aloop module to load.
Oh… and I just had an idea… If you do get snd-aloop loaded and looped into the VU meter it may be possible to just group a zone with the VU. That would be slick. Then you could have a dedicated Pi doing nothing but VUs.