There's not going to be any real way to remove that distortion without altering the quality of the original audio. What Randy did (or similar) is more or less going to be the end result no matter who you have try to fix it.
Fix it at the source. Here's how to keep this from happening next time:
1. Bring headphones and always monitor the audio coming into the camera. I can tell that you didn't check the audio until after the shoot because you never mentioned anything about trying to fix the problem during the show.
2. Learn the difference between
Line Level and
Mic Level and what they mean to your camera.
3. Confirm the type of output you are getting from the mixing board and know what it means.
Wolf
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