The latest version of the Spotify desktop client [18.104.22.1680.gc75ebdfd] misses the crucial option "Set the same volume level for all tracks". It is no longer possible to disable volume normalization.
This is downgrade is atrocious. Removing granularity from the options screen and forcing heavy audio processing degrades the value of Spotify to something suitable for non-paid background listening on Bluetooth boomboxes or laptop speakers.
While normalization is extremely useful for background music, the option of disabling it improves sound quality, particularly for listening to certain quetly recorded albums and classical music. It's a switch in the UI and should be brought back as soon as possible.
It seems to be the case that the normalization toggle never disabled all processing of the audio signal. But the option to disable volume normalization, which was added in early 2009, made the audio quality of Spotify usable for dynamic music and quality gear even before this service offered high bitrate streaming (mid 2009).
This setback in audio quality arrives at an unfortunate time when Spotify comptetitors are scrambling to provide lossless, cd-quality streams in several streaming intense markets. It's sad to see Spotify level the playing field by crippling its (partially) native desktop app, which could be a competetive edge. The competition, even the ones aiming for the audiophile crows, typically rely on useless, offline incompatible browser based offerings for desktop and laptop users.