you sure it's a compressor, doesn't it just adjust the volume ?

Yes. Its name is deceiving. It doesn't actually touch the volume, it's definitely a dynamic compressor.

It works slightly differently than a standard compressor but with the same end result. The reason, I think, is that Richard Lovejoy had never actually seen a studio compressor when he wrote Voladj. He basically fiddled with some code until it did what he wanted, and the end result was a dynamic compressor with funny parameter names.

For instance, a true compressor works by reducing the peaks of a signal, then increasing the overall gain of the signal. Richard's code constantly tries to increase the overall gain and backs off whenever it hits a peak. The end-result is the same, it's just two different ways of looking at the same problem.

Give it a try by installing the Hijack kernel. Voladj can be turned on and off from the Hijack menu. Later, after you've got it working, you can edit the config.ini file and put in your own parameters.