Bristol_Jonesey
Input gain MUST be set before the signal hits your AD converter - once it clips there, there's no way to reverse it one you've recorded it
Excellent advice, to which I would add some people who have interfaces with DSP think that by enabling compression or limiting, they'll prevent overloading the converters. But, 99.999% of the time this is DSP that works on the post-converter signals. If you want to make sure overs don't happen, you need to add something before the signal hits the interface input.
One exception is that some devices have a "soft clipping" option which is built into the analog mic pre, and therefore prior to conversion. This can be very handy for keeping nasty peaks from entering the signal chain, and the distortion is so fleeting it likely won't be noticed.
Also, I do realize that "tell them to use better mic technique" is along the same lines as "write a better chorus"

. But, when producing, I've often found that some people simply haven't thought about mic technique as a way to maintain consistent levels, and as soon as I point it out to them, they "get" it and it makes a big difference. k. d. Lang has fantastic mic technique - she plays a hand-held mic like a slide trombone. Find any videos of her singing live, and show it to the problematic singer. Once they see what the deal it, they'll understand.