Different volumes streaming Spotify

I stream Spotify and I'm fairly happy with it. When I listen, each song is at a different volume and I'm constantly adjusting the volume on my iPhone. Am I doing something wrong?  Can I resolve this.  I greatly appreciate any advice.  Doug  
That is because each recording is made at different volume levels and different amounts of compression.  You are not doing anything wrong. 

The ideal case is Spotify modify their app so when you play a song at a volume level you like, it remembers the setting and auto adjusts at the start.    But that is just wishful thinking, which is one step below making recordings without any compression.   Sigh.....   
I think there is a setting in Spotify to "normalize" all the tracks in a playlist. But if you are not using playlist, but selecting songs from different albums, then it will not work.
Yep, normalize. Technically, it degrades the sound somewhat, but it’s Spotify, non issue.
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