DVI, HDMI Adapters And Audio

Motherboards and graphics cards can come with no DVI->HDMI adapter and no HDMI output but still claim that they can do HDMI audio. Some people wonder if this works, but it does indeed.

The test subject:


This motherboard has no HDMI and no adapter, just the DVI. The audio codec for HDMI is embedded and it brings drivers for Windows and Linux support exists from Linux 2.6.30 kernel at least. Linux was hardware to get to work but it was possible with some minor adjustments. The embedded codec on the GeForce 8100 used here is Intel HDA compatible.

As long as motherboards and graphics cards claim support for HDMI audio you will be OK because the audio data is sent embedded in the same TMDS data channels that carry video. DVI looks like this:


We only care for DVI-D and DVI-I, which are the ones that bring the digital data channels. I have also never seen a living DVI-A and DVI-I is the most common type.
The HDMI adapter just routes the TMDS data channels - contaning both audio and video on enabled devices - to the equivalent pins and everything works transparently like if it was natively an HDMI port. There is no funky business here, it all simply works, since they are electrically compatible.
The situation is much different with DisplayPort, which needs active adapters to work with either DVI or HDMI.