AudioMasters

If I edit an mp3, when I save it will it be re-encoded?

I've been using Cool Edit Pro 2.1 for years. In it need to silence a bit of noise on a 48000 Hz 128 kbps mp3 (I demuxed from an .avi). Or do I need to use a dedicated mp3 editor if I want to avoid re-encoding?

Simple answer - yes. Audition only works in its native wav format.

It is also the case that, except for a few operations like breaking an mp3 file into two or more smaller mp3 files, the opposite: stitching smaller mp3 files into one larger mp3 file, and removing segments of an mp3 file, there is no editing of mp3 without first decoding it -- by any editor or other program, under whatever label. If the desired target is mp3, then the edited audio must be re-encoded after editing, with whatever resolution reduction and noise addition that entails.

Not so - take a look at http://mpesch3.de1.cc/mp3dc.html for starters - and I know there are some similar programs out there, I just don`t have a need forone.

I might be wrong on various aspects. I've only read about, not used any of these programs. However, I don't believe they are other than rather crude and limited editors. They are mainly for tasks like breaking an album mp3 into individual tracks, or reversing the process to make a single longer file. That functionally also allows for the "cut and paste" claim. From my reading, getting very exact selections of the audio is not easy.

Changing the volume apparently works but it is by changing some control information for each mp3 frame, not by changing the actual audio data as one would do with  amplifying .wav files.

I don't believe there is any functionally for tasks such as asked about: "silence a bit of noise"

Probably not and I missed that bit in the OP.  But then, that's not 'editing' in my book :) .

If you look at the feature list for the software Graeme mentioned, it doesn't actually go much beyond simple editing and basic level changes--it's certainly not a fully featured DAW.

I never implied that it was - it is a fully featured editor though.

I missed the OP bit about noise reduction and for that I'm sorry for misleading people as to the capabilities of this software, but NR is not editing. This is just another example of how the audio engineer's precise jargon has been hi-jacked and subsequently mis-used.

If one wants to do something that changes audio data, rather than just shuffle it around, it is necessary to first decode the mp3.

The only thing you can really do if you want to keep your original file as an MP3 is to save it at 320, but that doesn't help. It's always best to start with a WAV.

The other 'lossless editor' that springs to mind is "Machete" - http://www.machetesoft.com/home.html - does some video stuff too.

As with the other mp3 editors mentioned, the kind of changes the OP wanted to make are not possible.

Not sure if I've posted about this previously, but in the context of the OP's question, one needs to be very wary of the quality of decoders and encoders.

I recently needed to evaluate some audio in one of the Apple formats, and used "Super" to convert it to a wave file. I've used "Super" quite a bit in the past on video files, but this conversion was obviously unsatisfactory. In the end I downloaded and installed iTunes, which did convert reasonably well.

The problem now is that I keep getting pop-ups wanting me to update iTunes, download Safari and so on.  :x

I once installed iTunes and was unhappy with having its interference. A system restore point solved the problem. I didn't trust simply uninstalling it because too many applications that want to take over one's computer seem to not uninstall properly.

You might want to look at foobar2000. It handles a wide range of audio formats, has many third party plugins available, and has a very loyal following among people who are very concerned with computer audio from a certain perspective. It does not do things other than as asked to preform.
http://www.foobar2000.org/

In iTunes, go to Edit | Preferences, and on the first tab (General) near the bottom is the check box for checking for updates automatically; clear it.

Paul