I converted to Windows 8 and now I do not seem to have the “Stereo Mix” setting on the Recording tab on the Sound page. I have right-clicked on white space and checked the Show Disabled Devices and Show Disconnected Devices. No Stereo Mix; just a couple microphones, my webcam and Digital Audio (S/PDIF) choices.
How did you convert - install Windows 8 to replace the previous Windows version, install Windows 8 in another partition, or buy a new computer with Windows 8 installed?
If you installed Windows 8 on the same machine then you probably need to see if you can get updated sound device drivers meant for Windows 8, made by the computer or motherboard manufacturer. See Missing features - Audacity Support .
If you cannot get Windows 8 drivers, Windows 7 drivers may work, including any that came on a drivers CD with the original computer. Windows 8 audio is near-identical to Windows 7, but it’s possible the Windows 7 drivers may not have been recognised by Windows 8, perhaps because of some digital signing issue.
When I installed Windows 8 on my Windows 7 (HP) laptop, I found the built in audio device had gone back to drivers made by Microsoft, with the only input being the built-in mic. My solution was to run the Windows 7 audio drivers installer from the Windows 7 partition, which installed the HP-supplied audio drivers on Windows 8. The audio device now functions exactly as it did on Windows 7.