Speaking to Apple support they first tried passing it off as a Windows problem, when I pointed out it must be a recognised problem as there is an Apple website where the issue is mentioned - -gb/HT204923 But they could not help me beyond suggesting a reinstall of the Windows partition. Has anyone else had this issue with BootCamp 6.1 and resolved it? In the downloaded drivers with Windows Support Software there does not seem to be any audio drivers I can manually force an update with. I do notice that Windows stopped recognising the internal speaker as Cirrus and now is "High Definition Audio Device" I had an old version of BootCamp (5.xx) which had Cirrus drivers but Windows won't let me use these to update it's audio drives.