I am testing on and posting from a Lenovo laptop that has an Analog Devices Soundmax soundcard.
The initial install provided audio that worked OK for the basics of recording from the microphone and playing back though the speakers.
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The drivers in use were listed as 'Microsoft HD Audio', provided by Microsoft. Recording options were set to show disabled and disconnected devices.
Recording options were Microphone or CD.
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I then loaded in the Analog Devices drivers. With these, Recording Options were Microphone, CD or Stereo Mix. I have tested the Stereo Mix function and it works.
This implies to me that Microsoft is providing a driver that deliberately hides this function where the audio device supports it.
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I believe (but would be delighted to be proved wrong) that this indicates that Microsoft has joined some manufacturers in bowing to the lobbying from music and video industries to remove this essential function.
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FWIW, I worked in the broadcasting industry and started having to install third party software to provide this function to reporters and producers working to record and edit programmes away from their bases.
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It is a necessary function for many creative audio people, and if the hardware supports it, Microsoft's drivers should provide it.