I recorded sounds using a plug in microphone on a Windows 7 laptop. I used the Windows Sound recorder to record the sounds. It was only one microphone, but when I load the sound file into Audacity, it loads 2 channels. This is to be expected, but the sound files are slightly different (subtracting them from each other in MATLAB doesn't result in a zeroed signal).
Shouldn't they be copies of one another? I didn't use any special effects etc.