Very interesting topic and comments.
Although Peter's track is different from traditional O Gauge tubular track, IMO its appearance is very similar to it. The photos below show my ballast and tubular O Gauge track:
I don't know about how ballast affects sound because that was not an issue for me. However, I believe adding ballast helped stabilize my track so I have much fewer derailments.
My ballast consists of asphalt pebbles I got along the side of roads near my home. The pebbles are much bigger than O scale ballast, but the rails of the tubular track are also much bigger and higher than O scale rails. I guess that's why they call it high rail. Arnold