Hi,
1. Press Ctrl+p in the audacity main window.
2. Go to "Recording device" or so, don't know 100 percent how this option is labeled. Use tab to access it
3. Select Stereomix if you're able to find it. If not, your soundcard does'nt support recordings from it directly.
This mostly happens in windows7 were the audio drivers wich supported this great feature are'nt included anymore.
If you found the stereomix option, press enter. NNow it should work. Press r and do something that uses your soundcard, for example, let your screenreader speak something. Go back to audacity, press space to stop the recording, home to set the cursor position to the top and then press space again. See what happens!
If you can hear your Screenreader without other background sounds, all is right! Congratulations! You can record from your soundcard directly from now on!