Understanding 8-channel LPCM over HDMI: Why it Matters and Who Supports it

The Bandaid: The HDMI Sound Card

Ha! I lied; there's more.

No GPUs released in 2008 will support this protected audio path and thus we won't be able to get TrueHD/DTS-HD MA support from a GPU anytime soon. There is another option however: HDMI sound cards.

A couple of companies are working on sound cards with a built-in HDMI repeater, meaning there's an HDMI input, some logic to add data to the HDCP encrypted signal, and an HDMI output.

Your GPU would handle all video decoding and it would send its decoded but HDCP encrypted signal over HDMI, but instead of going to your display (or receiver or pre-processor) it would go next door to your sound card over HDMI (3dfx dongles anyone? At least these are lossless since they are digital signals... oh, hush, Monster).

The sound card would have an audio codec capable of ensuring a protected audio path and would handle all of the audio decoding/bitstreaming in the system. The audio from the sound card and the video from the HDMI input on the sound card would be combined, the HDCP repeated, and the new combined signal sent over HDMI to your receiver/display.

The HDMI spec allows for repeater support (as in devices that add something to an HDCP encrypted HDMI signal and pass along the new combined signal), so the HDMI sound card is really no different than sending HDMI to a receiver and then to your display. There should be no loss in quality or any other negative side effects if implemented properly.

ASUS and Auzentech are both working on these HDMI sound cards that should solve all of our HTPC problems. While both were supposed to be available over the summer, driver and software delays have pushed back both release dates to the last few months of 2008.

The Auzentech card

We have proof that the ASUS card was fully functional at Computex 2008; below are shots of the Xonar HDAV bitstreaming DTS-HD MA to an Onkyo receiver:

The test system

The Card

DVI to HDMI input, then HDMI output

It works!

We’ve got the ASUS card in house and are simply waiting for final drivers before testing it, so expect a review in the not too distant future.

I mainly wrote this quick guide to have something to link back to whenever I list 8-channel LPCM audio over HDMI as a feature. It’s not a typical PC feature like DirectX 10.1 or supporting SSE4, so it needed a little more of an explanation. And there you have it.