@Vitto Check out these forum links which discuss sound. You will have to make your own choice.
sound 1 sound 2 For what its worth, I screw directly into 1/2" baltic birch plywood. I've tried various noise deadening approaches and found they were not worth the bother. Reducing the plywood area (cookie cutter) to minimum does reduce noise but not eliminate. I understand solid rail (sans plastic roadbed) is quieter than rolled/tubular.
@Jeff_the_Coaster_Guy did a study around 2020 with a decibel meter showing results of different roadbed layers. homasote db test data This is a 2 page post with lots of interesting comments.
I find I use DCS to selectively reduce engine sounds while keeping other sounds at higher levels. Train running noise does not appear to be excessive to my ear, mainly because the engine sounds usually drown it out.
