Hi Ski, thanks for your reply, but I think we might have wires crossed, or maybe I should have started a new thread. I'm not at all concerned about file size, just about inputting the correct settings.
My problem now is that when I come to try to add my edited audio back to the movie, replacing the original crappy audio with its excessive noise, extreme variations in volume and feedback squeals, I get first to the "sound settings" dialogue - which I hope you can confirm I have selected the correct setting for, and secondly I then get the dialogue where I should be able to select my improved audio track.
In fact I am only being presented with the option to include the original bad audio track!
For e.g. in the particular project I'm working on, I have the original bad audio on track 1, a bounced denoised version on track 2 and then a further improved version on track 3. Tracks 1 and 2 are muted, because I assumed I'd be able to select my track 3 in the export dialogue which would then be added as the new audio file for the movie.
However, only track 1 audio is listed! I've tried at least a dozen times experimenting with different settings and will continue to experiment more, but I can't help but think this might be a known problem, or that you guys might possibly be able to diagnose where I'm going wrong.
Reading around online I think I can get there by using Quicktime Pro to add my bounced "improved audio" (and delete the old bad track) but surely it should work in Logic?