On my two Win XP machines, a stereo USB preamplifier is only able to submit the Left channel to the wave mapping layer. Win XP “generously” doubles this up into two mono channels (fake stereo) for any programme accessing either of the two Win APIs. I am not the first person to report this problem with Win XP (I cannot speak for Win 7,8). If I want audacity to receive genuine L/R stereo from my USB audio source, I have to dual-boot into Linux.
–Grahame
a stereo USB preamplifier
Whose name and part number is?
Koz
Hi Koz,
It’s a ART “Dual Pre USB 1.1” “Project Series” box, widely sold, but I cannot find it on the http://www.artproaudio.com web-site, which is puzzling.
It has been reported elsewhere that this problem has disappeared in Windows 7.
–Grahame
I have a feeling that this may arise because, during USB device enumeration, my USB stereo pre-amp is identified by Win XP as a “Microphone” and Win XP only allows one channel (L) for microphones! I do not know how to change that over to - say - “Line Input” which I reckon from past experience does get recorded in L/R stereo. 
–Grahame
What do you mean by “wave mapping layer”?
Do you mean when choosing MME or Windows DirectSound in Audacity Device Toolbar?
What inputs exactly do you have connected to left and right of the Art Dual Pre?
The product page is here http://artproaudio.com/art_products/signal_processing/usb_audio_devices/product/usb_dual_pre_ps/ and the manual here http://artproaudio.com/files/owners_manuals/om_usbdualpreps.pdf .
This is a common problem on Windows Vista and later and is solvable thus:
http://manual.audacityteam.org/o/man/faq_recording_how_to_s.html#rinstereo .
Windows XP does not usually have this problem (assuming you are sending stereo input) and doesn’t usually offer any such adjustment. Here is where to find the XP Sounds and Audio Devices: http://wiki.audacityteam.org/index.php?title=Mixer_Toolbar_Issues#xpcp .
You could try making Art the default sound recording device there and press “Advanced” but I would not be that hopeful.
Gale