Well its still not clear to me that you are not re encoding.
For example if you import all the sounds you need all will have been
decoded. When you do a mix it will be still not re encoded. Save a non
compressed master of this intermediate mix, then save your new mp3. If
changes are then required go back to the uncompressed version and add to
that, not the mp3.
Or use Reaper and simply save the project and do the editing afresh, but
that software is really hard to grasp and not good for simple stuff.
Brian

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"Bert Coules" wrote in message
o.uk...
Andy Burns wrote:

If you copy the file over and over, it'll retain the same quality, but if
you keep-re-encoding it, e.g. to mix in other channels each time, you'll
get gradually worse...

Thanks for that. I'm using a multichannel mixer (MixPad) so I can keep all
the components separate and just export the mix down to a single file when
I'm finished. But since many of the separate tracks are mp3 files the
subsequent final mixdown does represent a first-generation dub of many of
them. But you confirm my suspicion that no deterioration is involved.