Realtek UAD Driver is a third-party modification of Realtek drivers for older computers that support Realtek Legacy HDA FF00 drivers.

According to the developer: "I have an old system that is not supported by OEM specific Realtek UAD drivers, and I found HDA drivers to be very large, bloated and causing an unpleasant issue when equalizer was installed that was a pain to live with. Realtek UAD generic drivers were not affected, so I permanently switched to them. But Realtek doesn't provide complete and official UAD generic drivers very often so I decided to custom craft it from parts since I discovered it is possible to do so without breaking WHQL signature."

Installation:
Extract RTKVHD64.sys,RTAIODAT.DAT and hdxrt.cat to destination codec folder;
Save HDXRT.inf and HDXRTSST.inf to target codec folder;
Save HDX_GenericExt_RTK.inf and hdxrtext.cat to target ExtRtk folder and adjust in HDX_GenericExt_RTK.inf, DriverVer value to match with 'HDX_MsiExt_RTK.inf' from the downloaded RTK package;
Extract RealtekAPO, RealtekHSA and RealtekService folders from RTK package.

Remember, Realtek UAD Driver is a third-party modification only for older operating systems who need, and can't get, a working Realtek sound driver.

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What is Windows Hardware Quality Labs or WHQL?