Equal Loudness Normalizing for a dvd soundtrack

This is Audacity’s built-in dynamic range compressor: Audacity Manual

There are also several optional plug-ins for Audacity that perform dynamic range compression, including:
Chris’s dynamic range compressor
(1.2.7 beta - open source version: Chris Capel's Dynamic Compressor )
(1.2.6 - free but not GPL compatible version: Chris's Dynamic Compressor plugin for Audacity)

AGC (Automatic Gain Control)
Broadcast Limiter II
Broadcast Limiter III
Limiter (2)
Brick Wall Limiter
Classic Compressor 1.17 (VST effect for Windows)

The one that I would recommend for “Equal Loudness Normalizing for a dvd soundtrack” would be the 1.2.6 version of Chris’s Compressor because it is very simple to use and does a very good job. (you would probably want to increase the “Amount of compression” control up to about 0.7 or 0.8 but the other controls can be left at their default values).