If the proxy has a gear icon, select "Stream Media" or "Audio Optimized."
Type soundcloud.com/discover (not the login page). The Discover feed is lighter and streams faster. soundcloud unblocked 66 top
A good proxy page will show a "latency" time (under 200ms) and "WebSocket: Yes." If it doesn't support WebSockets, SoundCloud will crash. If the proxy has a gear icon, select