Sound is lower than other applications

[controlol]

Plan

Premium

Country

Netherlands

Device

any

My Question or Issue

I have been trying a couple of streaming services after I decided my 76000+ songs in my plex library still wasn't enough to serve the family. The rest of my family is very attracted to spotify. I am not so per se.

One thing I noticed was that the sound coming from the spotify is a lot softer than when I would play the same song via plex or groove music. 6db to be exact; this is witht the normal volume level. Then when you change it to loud, it's still 3db under the level I would expect. I noticed this as well when I connected my phone to my chromecast audio. The sound level meters from my mixer were a lot lower. I thought this was just something my phone (android 9) does, but it persists on my PC (windows 10 1809 update). 

One last thing I noticed was that the "normalize volume" was turned on when testing this. Which, when I think about a normalizer, brings the music all to the same volume, normally -0db again. But only when I turn the function off it would actually reach the -0db. Spotify has several normalize levels but not one that gives a -0db output.

I would like to keep the normalizer enabled but not have to change the gain on my mixer whenever I switch between plex and spotify.  

How could I solve this because a lot of my playlists are still in plex but I would like to slowly transition to spotify. The gain of my mixer is in a place I can't easily but to be frank I don't even want to have to do this. IMHO I think spotify as a "premium" service should be able to output -0db leveled music.