The problem is that the audio doesn't just contain clipping. It also has very shrill audio, at least judging by this sample. There's also some old vinyl/tape crackle and hiss, though that's somewhat easy to remove. Fixing the shrill is not going to be easy, if even possible. I quickly tried a few things for the shrill, and it either had no effect or actually made the audio worse.
I used a few of our custom filters in
Sound Forge to get here -- mostly the anti-clipping filters, after normalizing it to 30%. A few more were added to try and make it sounds better, but nothing was really to my satisfaction.
Find those here:
http://www.digitalfaq.com/forum/vide...io-filter.html
Somebody butchered the MP4 by starving the audio of bitrate. The noise won on the compression, hence shrill. You just need to locate better source. If it's an MP4 now, then something better exists, be it tape or a DVD.
Music makes for terrible blind samples. You need voices, unless there's a control to compare against.
Next time, also give us a WAV file ready to edit. Not an MP4 that we have to demux and convert first. Just be sure the original MP4 sounds identical to the WAV, and that converting didn't cause further loss.
