? Sound Soap for Audio, iMovie '09

[drdarrow]

I have a rather large time-investment into about 2 hours of compiled, digitized VHS clips from 20 year old tapes, using iMovie '09. (You get whatever you get, with 20-year-old video). I'd like to use SoundSoap to scrub out the tape hiss, which is the most prevalent and annoying thing about the sound.

How do I separate the audio from the video to do this, and still be able to replace it later? The duration of the audio clip must match the video clip exactly, or it will be/go out of sync.

BTW, I know how to "detach audio" -- which I have done -- but do not know what to do from there.

Thanks,

Dave