Comment 9 for bug 887922

Would you mind compiling, running and pasting the output of http://portaudio.com/trac/browser/portaudio/trunk/examples/pa_devs.c (direct link to c file: http://portaudio.com/trac/export/1796/portaudio/trunk/examples/pa_devs.c)?

It should compile with gcc -lportaudio -o pa_devs pa_devs.c; you may need to install portaudio19-dev first.

It'll list all the devices portaudio is seeing and give various info about them, hopefully it'll give a hint as to why Mixxx isn't displaying your microphone. I know you mentioned Audacity doesn't have any issues with it, but I think Audacity bundles its own copy of portaudio in its packages so it's possible there's some difference (also, knowing the info we're getting from PortAudio will likely be useful to know).