For the past several months I've avoided listening to Spotify on the Roku because the sound is so horrible. It sounds ultra compressed, definitely not the 320 kbps that is promised for premium users. I would say it's even below the 96 kbps that is for mobile users.
Unfortunately you can't select a bitrate on the Spotify Roku "Channel" like you can with other paid subscription services. So, there's no way for me to make adjustments myself.
I know that this has been a problem, but there doesn't seem to be a recent post, so I've posted one up.
BTW, it's that way for both my Roku Ultra (current version) and Roku 3 (2nd gen I believe). We are Premium subscribers. My streaming connection is fine, I can stream HD video via the usual apps (NetFlix, Hulu, SlingTv, Amazon Prime). I'm having to resort to Pandora for music.