copied from videohelp.com:

Threw together a soopa simple toolkit to address some of the low volume/low dialogue issues with transcoded AC3 files. Designed for neophytes, but can easily be customized by reading the documentation(s).

Features

-Converts your 5.1 file to another 5.1 file - No channel downmixing
-NOT lossless, but the transcoding quality is quite superior sounding
-Uses the new Aften AC3 encoder with SSE performance enhancements
-Uses the Wavegain limiter algo for additional volume and dynamic range reduction
-Simple 1 click batch file operation
-Doesn't Require Temporary WAV file creation


Example

in-example.ac3
out-example.ac3

Requirements

Avisynth v2.56 or Higher
.NET 1.1

Instructions

1) Download the AC3GAIN.ZIP file. Unzip to its own folder

http://www.bestsharing.com/files/hOM7tP ... N.zip.html

2) Drag Your AC3 file into the same folder as the AC3GAIN files

3) RENAME your AC3 file to INPUT.AC3

4) Double click on Run_AC3gain.bat to start

* A sample Input.ac3 file has been included for testing. Try it out first.

* The transcoding process might seem to lag in the beginning. It'll be stuck on 0% for the first few minutes, depending on the size of the AC3 - That's mostly due to Avisynth analyzing the file for volume peaks before applying DRC. It is still amazingly fast when Aften begins to transcode.

5) Completed file will be named OUTPUT.AC3 (384kbps, 5.1, 48000Hz)

Tweaking the Settings

AFTEN - Dolby Digital Dynamic Range Compression Profiles http://www.minnetonkaaudio.com/pdfs/Dol ... elines.pdf
To change DRC profiles in Aften, modify the following in Run_AC3gain.bat

bepipe.exe --script "import(^ac3gain.avs^)" - | aften.exe -v 0 -b 384 -dynrng 1 - output.ac3

0 = Film Light
1= Film Standard
2-4 = additional profiles
5 = none


AC3GAIN.AVS - Edit to suit the sound and volume level of your source file. See audiolimiter docs in source file section. You can REALLY make it loud, but you'll probably end up distorting. Test. Experiment. The following limiters are available.

http://forum.videohelp.com/viewtopic.php?t=317891