I've got some AVI files that I've processed via VDub, but the audio is too low on all of them... to different degrees. How do I normalize the audio without having to re-re-compress the video?

I really don't know where the best forum for this is, but since this has to do with my phone, I'll put it here. If the local mods don't think this is best here, feel free to boot me to somewhere else.