The free software Audacity has Compression used with Loudness Normalization effects that can be applied to your playlist.

The screenshot is a two song example showing a fairly large variation between the two songs volume levels that have these two effects applied. Using Labels after the effect have been applied will export each file separately into a folder and the exported songs will all be matched to the -14 LUFS level depicted in the 2nd screenshot. This technique can just as easily be applied to a 30 song playlist.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Songs Not Normalized.jpg (116.98 KB, 45 downloads)
-14 LUSFS Normalized.jpg (129.68 KB, 44 downloads)

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