Not convinced by 18d as "relaxing", it means "surrounding" to me.
I needed a lot of Googling to work out 20a as I know nothing of these modern popular beat combos
There is a genre of music referred to as 18d. It's very relaxing. Brian Eno's "Music for Airports" was the first example. If you have a while to spare, listen to the link!
Ianwil, I was exactly the same when it came to 20a, in fact that’s where I went wrong. I think 18d works as a genre of music. Chambers uses ‘relaxing’ in the definition