Just throwing it out there, would not be surprised depending on what gear I'd use, that the levels wouldn't necessarily be equal. I just saw this in another group as a response to a thread asking about Spotify vs CD comparo:
"It's got pretty difficult to objectively compare spotify to the CD since they've applied normalisation across the bored in order to obtain a loudness rating of -14 LUFS. This means modern loud masterings will sound even more flat and lifeless. Plus in the early days Spotify lacked quality control for the source of it's files. Some are bad CD rips and in some cases were already compressed." - JA Tooze
No, i'm glad you threw it out there. Kind of wish we would get more people to throw in their thoughts and opinions on this issue.
After I left the thread earlier, me and a few of the boys got into a discussion about it also. Seems like we came up with a general consensus about our conclusion, but no scientific reasoning as to why.
After a long ( to long ) discussion, we all sort of agreed the Spotify premium has a better (thicker) sounding midrange. While Amazon HD, had a better extension of the highs (and depth), while also having better (tighter) bass. The bass on Amazon also seemed to have more range, if that makes any sense.
For clarity, Spotify seemed to win out again in the midrange, yet Amazon HD won out in the highs and bass for clarity. And it was even harder to decide when it came to different genre's of music.
They had views on tidal also (but here I couldn't actually attest to one or the other, since it's been to long since I tried it). One thought Tidal was better than Amazon HD and one thought there was no difference.
So my conclusion is, there is no big winner. I may just try all three or four (throw in Qobuz) services for one month, to try and get an accurate assessment as possible.