this bug was reported to the Debian's bugtracker:
I can confirm the issue is still reproducible with the latest 0.21.16 release.
The original report follows:
When 'gwc' loads a .WAV file it shows two horizontal waveform bars, one
above the other. Presumably these represent the left & right channels
of a stereo sound file. The current help file and man page don't
explain it. Anyway...
The main screen shows two channels for a mono .WAV file. Both channels
look the same. Probably 'gwc' is making a copy of channel #1, and
displaying that as channel #2.
It's possible to hilite one channel and not the other. If I denoise
one bar or channel, (of a mono .WAV), then highlight both
channels and save it to a .WAV, the output file is mono. Therefore
'gwc' isn't converting mono data to stereo -- it's just displaying mono
data as if it were stereo, with separate highlighting for TWO tracks,
even though there's really just ONE.
For mono data it'd be better if 'gwc' showed one and only one waveform bar.
The present graphic is confusing.
Thanks in advance.