I don't know how normalization is done, but I do know that Spotify are very professional when it comes to audio quality. They do double-blind testing with setups by audio engineers to evaluate end-to-end quality when evaluating changes.
The double-blind scientific approach to audio testing ("ABX") has long been a major point of contention between "objectivists" and "subjectivists"[1]. This has been a godsend for the marketing marketing of some snake-oil companies in audiophile circles.
Really glad to know Spotify is on the side of science, here.
Do you mean double-blind testing benefits snake-oil companies? If so, may you expound on that? To my understanding, double-blind tests are meant to avoid un/conscious bias during testing.
No, on the contrary! Sorry for my ambiguous writing. Indeed double-blind is the only way to go.
What I meant is that there is a sizeable chunk of the audiophile industry (a certain press, electronics brands, stores and even studios themselves) that conveniently avoids any and all scientific testing, and promotes typical snake-oil "features" and "specs". Quite sadly for their abused customers.
One of the worst trends in my opinion was faking technical format quality by using different masters on each — with the shitty master on CD/MP3 and the good one, more dynamic, on DVD/SACD/vinyl etc. The latter always sounded better simply because it wasn't the same source!
In such matters, I guess we can trust Spotify based on their claims, and anecdotally I tend to believe them.
