Hi Harry,
The static/distortion is something I’ve never heard of.
I have the same experience, this is the first issue with playback I have had with Roon. My home / studio has around 7 Roon Endpoints ranging from Mac computers to an Airplay and Sonos system.
From my audio experience it sounds like some sort of buffer or audio stream issue, definitely tied to any form of DSP being added to the stream.
Have you tried the USB in combination with DSP volume settings on a different endpoint?
Yes. Tried a few tests this morning to try and narrow this down. The only endpoint that exhibits this static is the RPi. I created a few Zone Groups, and experimented with the issue. So three systems all grouped, and playing happily in sync and clean until I turn on “Volume Levelling” in the Zone settings. The result is all three zones dropping in level as expected but the RPi adds in the corrupted audio static, whist the other two endpoints the Zone Group are clean.
Here are two screen shots showing the Signal Paths of a test with just the RPi
No Static
Static
With respect to the 3.5mm jack: right now RoPieee is a digital endpoint only. The ‘raspberry Pi DAC’ option you tried is related to I2S devices.
Thanks for your help, and for an exciting project! I am intending to build some small self powered mono speakers for the house running your Ropieee.