Spotify Web App Equalizer. This solution works for both, the spotify windows store app and the traditional desktop app. Spotify is many things to many people, but one thing it lacks is an equalization feature for letting you adjust bands of bass, midrange, and treble.
Now, tap equalizer and turn it on. You need to have up to date windows 10 (post spring update). It integrates seamlesslty with spotify and is the only spotify equalizer available!
Spotify's latest ios app update rolls out today and adds a new equalizer to playback functionality.
A spotify visualizer was implemented in the desktop version of the app a while ago. Dependent on your network connection low: Equalizer for spotify is available for both android and ios mobile apps. I'm using the version 0.9.15.27 g87efe634.