I wonder if anyone has any opinions on this...
I produce audiobooks which generally end up mastered to 192kbps mp3.
By the time I've finished a project, I end up with multiple versions of my files as I move thorugh stages of editing, proofing and correction. Once a project is finished, I try to clean out any files I won't need so I can archive the project. However, being prudent, I feel I should keep the raw files, the final edited versions and the final mastered versions.
Recently, I figured I could save a lot of space if I just saved everything as 320kbps mp3, which brings me to the noise-reduction question:
Is it better to run noise-reduction on lossless (e.g. flac or wav) files, then save as mp3 - or will noise reduction on mp3 files be just as good?
The aim of my noise-redution is to eliminate line noise (I use a dynamic mic!) while not effecting the clarity of the recorded material.
In practice, the noise reduction seems perfectly fine on mp3 files to my ears (bearing in mind it's voice audio, not music), but I just wondered what the techinical standpoint might be?
Assuming you are carrying out the Noise Reduction in Audition you need to be aware that its native format is .wav. If you open an .mp3 in Audition it will automatically be converted to .wav. So that is the format in which your NR processing takes place.
If, after carrying out your NR process you then re-encode the file as .mp3 you will introduce one further stage of lossiness (=audio degradation); each re-encoding of a lossy format, like .mp3, will introduce additional "losses" which, contrary to the belief of some, can never be restored, any loss is permanent!
The general rule is that Recording/Editing/Processing of an audio file should always be carried out on a completely lossless copy of the file, i.e., wav, incrementally saving it as .wav and saving as .mp3 only when the finished product is ready for distribution and no further editing or processing is intended or needed.
Thanks for the answer, you're confirming what I already knew really - although I would say in practice my results with mp3 have been entirely acceptable especially since nobody (or very few people) are looking for an audiophile experience when it comes to audiobooks. That said, it feels better to stick to convention and use lossless format all the way to final mastering, a standard I would never dream of deviating from when working with music production. I would hope, however that there would be no problem using flac rather than wav, just for a bit of space saving, my hard drives fill up pretty quickly!