This is a very old ask and nothing has been done to deliver it, so don’t hold your breath. This does not affect album play where the sound levels do not change across tracks, but it can make playlists close to unusable, where different tracks from different albums are in the list. Many of my lists are curated to keep only such songs that play at the same sound level. Not ideal, but what’s the alternative?!

Accomplishing this is very hard because there is no applicable industry standard. Essentially, all tracks in a playlist must be played and catalogued before the level can be set, then a note must be kept somewhere for each track, but SONOS cannot modify tracks stored on music service servers. Each service potentially offers tens of millions of tracks. Tracks can can be reissued with a different level and there will be tracks that have not yet been recorded.

There is a playback process called “compression” that could be used to solve this problem. Unfortunately, the marketplace has rejected this concept.

@Big Alan,
Sonos do not apply any volume normalisation to files from any music source and perhaps rightly so in some peoples view.

However, Sonos apparently can and do alter the playback levels using the ITUNNORM or REPLAYGAIN_TRACKGAIN tags in the embedded metadata for a track.

When it comes to general streaming music services though - and this includes things like Plex - it really depends on whether those mentioned tags are passed by the service to Sonos players, or not.

I understand that you can point Sonos to a local Music Library on a NAS or PC etc. and if the tags are present, or you insert them yourself with a Tag editor, like MP3Tag for example, then Sonos will apply the normalisation. 

I hope that helps.