I use Audacity, but I don't suggest using the normalize function.

Why?

If song A has a loud part near the end, and song B has a constant value, normalize will adjust both to be as loud as it can. It does this by using the loudest part of the song and maximizing that.

They effect would be the loudest part of song A would be at the same volume as the entire song B, the result would be that song A sounds softer than song B, unitil it hits the end.

This is what I discovered when I started making backing tracks for my duo http://www.s-cats.com

I have found no easy way out. I have a few songs I use as reference tracks. One disco, one energetic rock, one mellow rock, one cool school jazz one soft dinner-music set song, etc.. Sometimes a few in each genre.

Then I play the new song and the reference song back-to-back and use Audacity and my ears to get the new song close to the reference track.

If anyone has an easier way to do this, I'm all ears.

BTW, years ago I tried an app that was supposed to make them all seem like the same volume by adjusting the average volume. Thoughtfully, I made a copy of the tracks in a separate folder, ran the app on that folder and tested. The results were worse than normalizing the whole bunch. Some were much louder than others.

Notes ♫

Bob "Notes" Norton smile Norton Music
https://www.nortonmusic.com

100% MIDI Super-Styles recorded by live, pro, studio musicians for a live groove
& Fake Disks for MIDI and/or RealTracks