8-channel LPCM over HDMI

You may have heard that I've recently become somewhat infatuated with HTPCs. I've been hammering on all of the AnandTech staffers to start looking at the needs of HTPC enthusiasts, and I've personally been on a bit of a quest to find the perfect HTPC components.

Blu-ray (and HD-DVD) both support Dolby TrueHD and DTS-HD audio encoding, which offer discrete 8-channel audio output. The problem is that there's currently no way to send a TrueHD or DTS-HD encoded stream from a PC over HDMI to a receiver, the stream must be decoded on the PC. Cyberlink's PowerDVD will decode these high definition audio formats just as well as any receiver into 8-channel LPCM audio, but you need support for sending 8-channel LPCM over HDMI.

Most graphics cards that implement HDMI simply pass SPDIF from the motherboard's audio codec over HDMI, which is unfortunately only enough for 2-channel LPCM or 6-channel encoded Dolby Digital/DTS audio. Chipsets with integrated graphics such as NVIDIA's GeForce 8200 and Intel's G35 will output 8-channel LPCM over HDMI, but AMD's 780G will not.

All of AMD's Radeon HD graphics cards have shipped with their own audio codec, but the Radeon HD 4800 series of cards finally adds support for 8-channel LPCM output over HDMI. This is a huge deal for HTPC enthusiasts because now you can output 8-channel audio over HDMI in a motherboard agnostic solution. We still don't have support for bitstreaming TrueHD/DTS-HD MA and most likely won't anytime this year from a GPU alone, but there are some other solutions in the works for 2008.

To use the 8-channel LPCM output simply configure your media player to decode all audio streams and output them as 8-channel audio. HDMI output is possible courtesy of a DVI-to-HDMI adapter bundled with the card; AMD sends audio data over the DVI interface which is then sent over HDMI using the adapter.

Index NVIDIA's Unexpected Response


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  • formulav8 - Sunday, June 22, 2008 - link

    I know this is a late reply but I will do it anyways. :)

    I am just going by what your testbed specs says...


    Video Drivers

    Catalyst 8.5
    ForceWare 177.34 (for GT200)
    ForceWare 175.16 (everything else)


    If you used Beta drivers you probably should have updated that in the specs and whether they are based on 3.5 or 3.6. It would still be nice to see some results with the new official 3.6 driver though. :)

  • formulav8 - Sunday, June 22, 2008 - link

    I meant to say 8.5 and 8.6 not 3.5 and 3.6 :)

  • goinginstyle - Friday, June 20, 2008 - link

    Is the beta based on 8.5 or 8.6? Reply
  • jpeyton - Friday, June 20, 2008 - link

    Newegg had the Asus 4850 for $199 with a $30 MIR to bring the total to $169.

    People are reporting seeing the Visiontek 4850 on Best Buy shelves for $199, but this week's ad has all Visiontek video cards at 25% off, so that brings it down to $149.

    $149 for a 9800 GTX killer? AMD is turning the GPU price/performance market on its head overnight with this release.
  • jovdes018 - Friday, June 20, 2008 - link

    only if amd/ati could polish performance scaling with future drivers, 4870x2 in crossfire mode would really hit a hammer on every nvdian head.im so exited!!! Reply
  • BikeDude - Friday, June 20, 2008 - link

    and how do these cards perform playing movies? Without resorting to the malware package aka "PowerDVD"? Reply
  • msgclb - Friday, June 20, 2008 - link

    On your Crysis benchmarks why don’t you tell us if you’re using AA. You do for most of the other benchmarks. Does the lack of any AA = No AA? I was going to ask DX9/DX10, 32-bit/64-bit but you do list your operating system as Windows Vista Ultimate 64-bit SP1 so I’m guessing that you’re using 64-bit DX10.

    I get lousy Crysis results using Vista 64-bit DX10 with my dual 8800 GT SLI system but I get better scores than yours if I use DX9.

    I appreciate all the work you put in to keep us informed.
  • DerekWilson - Friday, June 20, 2008 - link

    we do 64-bit dx10 noAA for crysis. Reply
  • bob4432 - Friday, June 20, 2008 - link

    hopefully this will drop the price of the 3850 :) Reply
  • GlassHouse69 - Friday, June 20, 2008 - link

    When is a tech company going to stop sucking NDA manchicken?

    anadtech has lots of bruises on their knees.

    "stay tuned kids for the 4870 while we polish off this knob!"

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