in Audacity: Load your audio file. (Video file didnt work for me, i had to convert it to an audio before I could process the file, in my case it was a vob file) Once loaded, select the area you want to filter/extract voice of. (Sample it first, then get excited ... :)) Then go to Effects tab and scroll down until u see Low Pass filter. Play with the parameters and im sure you will have the solution there.