Ensure you have the Conexant SmartAudio HD driver installed. You should see it under Sound, Video and Game Controllers in Device Manager. With the Conexant driver already installed and working the key is finding the exact location of the driver file. It might vary from one computer to another and also be called something else. Mine was called chdrt.inf and it was located in:
C:\Windows\System32\DriverStore\FileRepository\chdrt.inf_amd64_neutral_fa34defac299c440
If you are not sure where your .inf file is located you could do a windows search for text in files of the string:
EpSettings\StereoMixEnable. It will most likely be a file with the extension .inf and be located in a sub folder
of the System32 folder.
Right click on the .inf filename and select "Open With" then choose Notepad. Hit Control+F then search for StereoMix to find the three lines:
;HKR,%EPattributePath%\EpSettings\StereoMixEnable,Enable,1,01
;HKR,%EPattributePath%\EpSettings\StereoMixEnable,MixAssocSeq,1,E0,E0
;HKR,%EPattributePath%\EpSettings\StereoMixEnable,MuteGainSettings,1,00,00
Delete the semi-colons --> ; and save the file. However Windows won't let you save the .inf file
unless you change the files permissions. This gets complicated and a bit dangerous!
Basically right click on the .inf and then click these tabs/buttons.. Properties> Security>Advanced>Owner. The current owner should be TrustedInstaller. Change this to an account on your computer that has Administrator rights and you can log in as. So Click on Edit and in the "Change Owner To:" field there should be an entry there such as: Administrators (Your computer name\Administrators) so choose that then Ok and apply and Ok to close out all the dialog boxes.
Now right click on the .inf file again: Properties>Security>Edit>Select "Everyone"
in "Group or User Names">Select checkbox for "Write" in the "Permissions for Everyone" section>Hit Apply and OK
your way to close all the dialog boxes. Now you can save the .inf file you deleted the semi-colons from!
This step is VERY important. You must change back the permissions to the way they were. Right click on the .inf and as before change the Write permission by deselecting the checkbox for "Write" and also then change the Ownership of the .inf file back to TrustedInstaller. This time you go Owner>Edit>Other Users or Groups and type in NT SERVICE\TrustedInstaller in the box and hit Check Names then Ok and Apply your way out of the dialog boxes.
Now finally re-install the driver: Here I got problems with the driver not being recognised and possibly it was because Windows 7 64 bit was saying it is not digitally signed so here's what I did: Start Menu>Right click Command Prompt>Run as administrator>type in this command and hit enter... bcdedit /set nointegritychecks ON.
To install the driver: Device Manager>Sound, Video and Game Controllers>Right click on Conexant SmartAudio HD>Update Driver Software>Browse my computer for driver software>Let me pick from a list..>Have Disk>Browse>Now in here you need to find the location of the .inf file you just edited, in my case I pasted in the path to the folder and hit enter then selected the chrdt.inf file and hit OK. When it was installed I went back to the command line as before and ran the command: bcdedit /set nointegritychecks OFF
Now I rebooted the computer and this time Stereo Mix DID show up in Control Panel > Sound > Recording Tab after right clicking on empty space and selecting Show Disabled and Show Disconnected Devices.