This was the problem: I had two mp3
track_11 (fhg 192 kbps_4:06 sec) with an incomplete abrupt end
track_12 (fhg 192 kbps_5:49 sec) begins with the last second of the track_11

So I joined these two mp3s using the join tool of encspot pro (append mp3).
Once I got the joined file I split the file again in the correct times with mp3DirecCut.
Conclusions, I got the two files with their correct length
track_11 (fhg 192 kbps_4:07 sec) checked with mp3trim - no errors and natural end.
track_12 (fhg 192 kbps_5:48 sec) checked with mp3trim - no errors and natural end.

The ID3 tags are also fine

So my question is if I lost any quality in the process.

Thanks in advance for any help and best regards
Ryo

...nothing that matters..., maybe a few samples

Thanks for reply, there is another mp3 program to join/split files in a safe way with no loose of quality?

There are two/three I remember in no time, for more I have to have a look at my audio-tools-folder at home

Musicutter

mp3 splitter & joiner (shareware)

Maybe DirectCut can help you too

Thanks!