I've been using TimeMachine to record late night music radio programmes.
I'm pretty sure I didn't do anything different, but one recording is
significantly quieter than the others and the quiet one shows up as
of type 'Unknown (model/x.stl-binary)' in Nemo file manager, whereas
the good ones are of type 'Binary (application/octet-stream)'.
'file' says they are all Sony Wave64 RIFF data, WAVE 64 audio, stereo 48k
sox (-n stat) seems to show significant differences: