I have windows xp. The recordings were fine until a couple of weeks ago. All of a sudden, all line ins and microphones are recorded in stereo but with both channels identical, as if in mono. Help.
Audacity records in two channels or one channel. There is no other relevant Audacity setting. If your sound source sends mono then Audacity cannot make a stereo track out of it, only a dual mono track in which both channels are the same.
Windows Vista/7 has an operating system control to record in stereo or mono. Windows XP does not, so you will need to look in the control panel for your sound card and examine if you are actually sending stereo or mono to the input. Even if you are sending stereo, most microphone inputs are mono, except in a few laptops or netbooks/notebooks where the mic input adapts to the input being mono or stereo.
So in a nutshell you have to look outside Audacity for the cause. If you are sending multiple mic and line inputs from a mixer, look in the mixer.
Gale
How come it happened just a short time ago, without any warning? It worked fine up to then. Did the sound card malfunctioned? How can I figure out?
We cannot see over your shoulder, unfortunately, and so cannot begin to help you without much more information about what sound card(s) and external audio devices you have and how microphones and other recording inputs are connected.
You could possibly try a System Restore if you have that enabled in Windows XP, but there is no guarantee that would help:
http://support.microsoft.com/kb/306084 .
Gale