Recorded an audio file using microphone via Windows Sound recorder, but has 2 channels that are slightly different. Why are they different? 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.

Thanks
I am not %100 sure, but it sounds like you are recording the file in stereo. If this is the case, then Windows Sound recorder is taking stereo input, which means it's accessing 2 AD converters which have the same input applied to them. The difference between the two signals in this case would be the noise and any offset between the two converters.

I would see if Windows Sound Recorder could make a mono recording, or else use another program to make the recording.