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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  • docmilo - Thursday, June 19, 2008 - link

    I browsed on over to the Egg and did a search on 4850. A whole bunch of cards popped up at $199.99 and one even has a rebate! I wonder how long until it stops saying "Buy Now" and goes to "Autonotify". Reply
  • chizow - Thursday, June 19, 2008 - link

    You guys did a nice job of covering both the pros and cons of the 4850 and CF, showing some of the pitfalls of relying on multi-GPU solutions for performance. You also made mention that similar performance gains were seen long ago with the 8800GT.

    That said the 4850 is certainly a good part from AMD and there's definitely some very interesting things they've done with this card. You hinted at a lot of them with the architectural changes but there's a few other sites that hinted at some of the changes. Its clear ATI has drastically improved their memory controllers and cache design along with their render back ends for AA performance.

    I think the real thing to keep an eye on though is how AMD managed to get near 100% scaling with CF. Extremetech hinted at improved memory controllers and a gpu communications "Hub" here http://www.extremetech.com/article2/0,2845,2320865...">http://www.extremetech.com/article2/0,2845,2320865... for improved performance between GPUs. I'm sure you guys will cover these improvements in detail in your complete review, but it looks like that hyper transport mechanism you alluded to.
  • MadBoris - Thursday, June 19, 2008 - link

    Nice to see AMD staying competitive, plus keeping prices down.
    I think the days of me spending $400+ on a video card are behind me, atleast for the foreseeable future. You have to provide alot more than 10% performance increases for an extra $250 NVIDIA.

    I'm rather surprised NVIDIA has not really capitalized on taking a huge performance lead and crown with all the AMD post merger dust settling.

    I'm pleasantly surprised that AMD is continuing to excel with HW. If only they would bring back an AIW card, I'd buy one, but my current 8800GTS is not so outmatched that it is worth upgrading to anything this generation.
    Good article Anand.
  • fungmak - Thursday, June 19, 2008 - link

    Looking at the CF perfomance of other sites who used cat 8.6, IIRC were a lot better than the current AT results.

    Just wondering if there is an intention to update using cat 8.6?
  • derek85 - Friday, June 20, 2008 - link

    I second this, I'm sure 8.6 came with some nice optimizations on 770s. Reply
  • DerekWilson - Friday, June 20, 2008 - link

    we did not use catalyst 8.5 drivers.

    we used the very latest beta drivers ATI could get us.
  • Wirmish - Friday, June 20, 2008 - link

    And did you use the Radeon HD 4800 Series Hotfix (6/20/2008) ?


  • Nighteye2 - Thursday, June 19, 2008 - link

    The big question for the comparison between this card in CF and the GT200 will not be the classic framerates here - but the performance of games that use the GPU for part of the physics processing. The GT200 has lots of compute power to spare for physics, can 2 4850's in CF match that?
  • FITCamaro - Friday, June 20, 2008 - link

    With 800 shaders it wouldn't surprise me. Reply
  • Wirmish - Friday, June 20, 2008 - link

    He talk about CF...

    So it's 1600 shaders !

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