On 18/05/2020 19:27, Bert Coules wrote:
Perhaps only peripherally DIY but there's such a lot of computer
expertise here.

I was surprised today to see a reference to "a poor quality
fifth-generation mp3 file" - I thought that digital files (of whatever
format) reproduced exactly from generation to generation with no
deterioration at all.Â* Am I mistaken?

Yes. MP3 is a compressed audio stream uncompressed when you listen to
it. You can crop and do certain other things to it losslessly but in
general if you change things like amplitude slightly then it will be
recompressed with additional quantisation losses every time you do it.

Standard approach for audio as with JPEG images is to keep all the
intermediate working files in some lossless format like FLAC.

https://en.wikipedia.org/wiki/FLAC

There are transcoders that can do the available MP3 lossless operations
directly on an MP3 stream to splice things together for example.

If mp3s do indeed get
progressively worse when repeatedly dubbed I'm going to have to rethink
the audio project I'm currently working on.

Yes. Although depending on your final quality requirements you might get
away with it if you keep the bitrate high enough.

Sound files are generally small enough that using FLAC isn't too bad.
Then you have a single generation lossy recoding right at the end.

There is a very slight advantage to using about the same compression
quality parameters as your original source material.

--
Regards,
Martin Brown