How to make a MP3 track to gain its DB level evenly?

How do I make a MP3 track to gain its DB level evenly enough, ie. auto gain process, for each smallest time block ?
Is there a vst plugin for doing it, or any other free software
I did it with the disappointing result that make the track fluctuating in DB/volume, although it’s done by no-free application - Goldwave.

If it’s music try this Audacity plugin … AGC - Automatic Gain Control
If it’s speech try this Audacity plugin … Improved "leveling" for speech - #27 by Trebor

I downloaded, Thanks so much.