Thank you! This was one of the last things to get working. Working well!Updated 07/3/2018. This solution works in High Sierra 10.13.6 as well as several previous versions of MacOS. I didn't create the tools I only figured out how to use them. Credit for the kext goes to andrejkw at macrumors. Your mileage may vary but this is the easiest solution I've found. I've used it for years & its worked for many others. Definitely worth a try.
1. Download package located here https://www.dropbox.com/s/8hay1m0rec93vvo/HDMIAudio-1.0.dmg?dl=1
2. Mount HDMIAudio-1.0 disk image
3. Mount your EFI partition. You may need to use Clover Configurator or similar tool to do this.
3. Copy HDMIAudio.kext from the HDMIAudio disk image to EFI/Clover/Kexts/Other
4. Reboot. Clover may hang on the initial boot attempt, if so a restart of the computer should have you up and running.
There you have it, a simple file copy.
After the reboot I had working HDMI Audio.
*If you don't see any audio devices after reboot. Download and run AudioCloverALC command by toleda
This may help to finish off the install.
If you're confused, there is a quick rundown in this video. *VIDEO IS OLD. COPY KEXT TO "OTHER" FOLDER!
*Don't forget to select the proper output! System Preferences/Sound/output or hold the Option key while clicking volume icon.
So now you have HDMI audio, but what about volume control? OSX doesn't support volume control of HDMI devices natively. Use one of the utilities below to enable it.
@iphillips77, this is great! This is the missing piece that saved me. I kept going back and forth attempting Toleda's guide and then trying this kext fix, but couldn't get DisplayPort audio back in High Sierra after update. Thanks so much for sharing this.Recent versions of macOS (10.13.4 and above or so) have deleted some nvidia device IDs from com.apple.driver.AppleHDAController. This prevents some cards from working that should -- if you have upgraded and are having trouble this might get you up and running.
Fire up your copy of IORegistryExplorer and search for HDAU. Select, and look for your vendor and device IDs. Vendor-id will be <de 10 00 00> for nvidia cards, device-id will be <xx xx 00 00> -- xx xx is your device ID. Make a note of it. Mine was <ba 0f 00 00>, yours is probably not.
Open your clover config.plist in clover configurator. In the "kernel and kext patches" section, create a new entry under KextsToPatch. Use com.apple.driver.AppleHDAController as the kext name. Put DE101A0E in the "find" column, and DE10XXXX in the "replace" column, replacing XXXX with your device ID. I put DE10BA0F there.
This patches AppleHDAController on the fly, replacing one of the valid IDs with your card's ID. That was enough for me to get HDMIAudio.kext to work as well as it did in 10.12 Sierra.