How to get Boot Camp Audio Drivers for Windows 10 on High Sierra?
Often the audio drivers fail to work when Windows is installed using either the wrong Boot Camp Support Software (Windows Support Software) or Windows is installed using the wrong boot method (BIOS vs EFI). 

The best way to get the correct Boot Camp Support Software is to either use the Boot Camp Assistant to download the software or use the Boot Camp Assistant to install Windows. 

Usually, Windows 10 installs for an EFI boot on Macs that Apple documents to officially support Windows 10. Otherwise, Windows 10 should be installed to use the BIOS boot method.

If you need help determining which boot method Windows is using, post a comment including the model/year of your Mac.