Stereo Mix For Conexant Sound Card

1. Download driver from your notebook vendor eg: im use Satellite M840
2. Find *.inf file name..  in my case TE7Pebwa.inf

3. Find 

;HKR,%EPattributePath%\EpSettings\StereoMixEnable,Enable,1,01 

;HKR,%EPattributePath%\EpSettings\StereoMixEnable,MixAssocSeq,1,E0,E0 

;HKR,%EPattributePath%\EpSettings\StereoMixEnable,MuteGainSettings,1,00,00

4. Remove ; to enable StereoMix 

5.Open up Device Manager. then click on "Settings", then "Control Panel". From there, click on "Hardware and Sound", then "Device Manager".
Expand the "Sound, video and game controllers" pane, right-click on "Conexant SmartAudio HD" then click on "Update Driver Software..."
A new window should pop up. Click on "Browse my computer for driver software", then click on "Let me pick from a list of device drivers on my computer".
Click on the "Have disk..." button, then navigate to the folder which contains the modified *.inf file.
During the installation process, a pop-up window will appear, saying that "Windows cannot verify the publisher of this driver software". Click on "Install this driver software anyway", after all you only modified a single file that was downloaded from your laptop manufacturer's driver page

6.Window should say that your driver software has been installed successfully. Close the window, then restart your computer.
When you're on the desktop, right-click on the speaker icon on the taskbar, next to the clock

7. Click on "Recording devices".
Right-click on the window, then check the "Show Disabled Devices" and "Show Disconnected Devices" options.

The Stereo Mix device should appear greyed-out. Right-click on it, then click on "Enable".