RealTek/Windows 20khz Cut Off

I have previously on a different PC recorded the stereo mix in Audacity, whilst playing a CD and would get the full frequency range of the CD. On my current PC I now get a 20khz cut off, despite changing the settings (the sample rate and bit despth) on the playback and recording devices in Windows and also in Audacity. Does anyone know why this would be, and if there is any way of correcting it?
 
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