The HTPC / Windows 7 Chronicles: You Asked, We Answer!

Do We Have A PAP? Is 7.1-Channel LPCM The Answer?

We had an anonymous reader ask if the Maui platform facilitates a protected audio path, and the short answer is: no.

Why did the reader ask about a PAP? Because, in order to play back today’s high-definition lossless audio formats, such as Dolby TrueHD and DTS-HD Master Audio, a Protected Audio Path must exist between the content itself and the software application decoding it. In essence, the AACS (Advanced Access Content System) wants to make sure a user can’t snoop the bus and copy the lossless stream.

AMD is convinced that the MSI Media Live board meets the AACS requirements. Though it could be argued that PCI Express is a user-accessible bus, AMD says only the D2Audio can read it. Nevertheless, our Maui platform is not yet able to put out lossless TrueHD or DTS-HD MA audio, because the software is passing down-sampled audio to the hardware. Slowly but surely, software vendors like Cyberlink and ArcSoft are working with the audio controller and codec folks to certify protected paths where they can (there is currently one discrete sound card able to do HDMI pass-through and two Reaktek codecs capable of 96 kHz/24-bit DVD playback across four to eight channels).

Even if you're able to decode DTS-HD and pass LPCM audio, you aren't getting the 24-bit resolution offered by the Live Free or Die Hard soundtrack

Currently, the only way to enable a PAP and play back 24-bit/96kHz multi-channel audio is using Asus’ Xonar HDAV 1.3, which we’ll be looking at on the following page. Auzentech has been working on an X-Fi Home Theater HD card with similar functionality (paired with PowerDVD 9), but as of this writing, it remains unavailable.

The best you can hope for from MSI’s Media Live board, then, is the equivalent of DVD-quality audio—Dolby Digital and DTS. So, for the reader who said he’d upgrade as soon as he could get a Protected Audio Path via HDMI: you can, but not (yet) with the D2Audio chip onboard.

The good news is that you’d be truly hard-pressed to tell the difference. Also, you'd need to test with the right source content if you ever hoped to try to hear 24-bit versus 16-bit resolution. Not all movies take full advantage of the capabilities of Blu-ray. Many natively employ 16-bit/48 kHz sound anyway. And very, very few even offer 96 kHz sampling. Concert DVDs are the exception, and I purchased The Police: Certifiable in Bueno Aires (24-bit, 96kHz) as sample content.

Played back as multi-channel LPCM audio on a G45- or GeForce 9300-based system, it'd be converted to 16-bit/48 kHz. Now, I can't claim my equipment is high-end enough to expose the difference between CD-quality and high-resolution playback, but I do crank the volume in the music and movies I enjoy, so if the higher resolution sound is expected to demonstrate advantages in the noise floor at significant levels, I'd hope to hear that. In truth, it remains difficult to qualify the improvement. The Police concert DVD also included a pair of CDs, enabling a comparison to stereo ouput of the same songs. But the mixing was so different as to render the two incomparable, in my opinion.

The Workaround…Sort Of

So, you’ve likely read that multi-channel LPCM is the way around this whole confusing audio situation. In a way, it really is—especially if you need eight-channel output rather than six. You can build an HTPC based on Nvidia’s GeForce 9300 chipset, use PowerDVD 9 to decode the Dolby TrueHD or DTS-HD signal, and output 7.1 channels of linear PCM audio the same way a Playstation 3 does. The receiver simply plays back the discrete audio streams, oblivious to the original encoded format.

Note the DTS-HD being output as 48kHz/16-bit LPCM audio

However, you lose the bit-for-bit lossless quality as soon as the software decoder passes the signal out over HDMI. What’s more, there’s a fair chance that, even on a GeForce 9300 or G45, multi-channel LPCM will never yield 24-bit audio (or 96 kHz sampling, if you have one of the few discs offering that). You see, the same restrictions that apply to Maui playing back lossless audio through the D2Audio amp limit PowerDVD and TotalMedia Theatre to playing back CD-quality sound currently.

Both vendors naturally know there are audiophiles who still clamor for such a capability, but of course, their hands are tied by the standards bodies licensing them the technology to do any of this. Thus, as of today, the only real answer for bitstreaming lossless audio is Asus’ Xonar HDAV 1.3. Every other alternative gives up something—regardless of whether you can actually tell the difference.

Here's what your receiver displays if your playback software does the decoding and outputs multi-channel LPCM sound...
Chris Angelini
Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.
  • WheelsOfConfusion
    Nice follow-up. A bit more entertaining than benchmarking the same suite of games over and over, I'll bet.
    Unfortunately you ran into that DRM breakdown problem, where one snagged link in the hardware/software chain negated the high-quality features we're supposed to be enjoying through "easy" and "transparent" copy protection schemes. DRM will make criminals of us all, one way or another: if not by trying to get around it, then when we go on a bloody rampage out of frustration from trying to make it work.
  • mcboj
    Nice article. Made for a good read, as I'm wanting to build a HTPC very soon. Seems crazy that the combined might of all these manufacturers aren't able to make this work 100% yet. Too many cooks in the kitchen?
  • Luscious
    Great article. I've been looking into getting BD content onto a HTPC but have run into the same DRM and audio issues as you describe. DVD's were a lot easier to deal with, but BD is an entirely different animal. True, I've yet to experiment with Win7 and have only touched Vista and MCE so far. I'm probably going to wait a few more months for Win7 to show before I look into it further.

    I do agree in your choice of a dedicated receiver. I've got an Onkyo receiver connected to Yamaha speakers in a 7.1 arrangement that I use primarily as a source switch. Originally I had three DVD changers that I replaced with a HTPC. It's worked well, but now with a growing BD library I need to take a second look at my system. Unlike you, however, I chose to go with a dedicated gaming box alongside with passive PSU, passive GPU and a silent CPU heatsink for big-screen gaming. The multiple HDMI and audio inputs on the receiver helped out big time. I also have a dedicated BD player at the moment that I'll probably keep just in case.
  • empstar
    Hi I'm new to HDTV or HDPC I'm using the laptop(HP media DV1125 C2D, ATI 4650) to connect to my SONY 32" LCD TV 100MHz motion flow (32W550 just bough it on 04july09) using HDMI cable 1920x1024 Max Res. but the picture/win desktop look ugly and the front in the windows exploere look
    ugly too. Q1) how to SET? the best res? and Q2) should I use HDMI or PC-input (D-Sub 15 pin) to connect? DVD player connected to watch movie look great. HELP... some one?
  • quadrophenia
    I thought I read somewhere that Maui does not work if you don't have an HD tv. Can anyone confirm this? Thanks
  • kazius
    There are a lot of factors that you didn't factor in: room acoustics, speaker quality, speaker placement (NEVER place the speakers directly in the corner - like as seen in the pictures), and so on. These make the audio comparison a moot point - I'd expect a richer low end may actually harm the overall listening experience in such a setup, inaccurate spectral positioning, and a somewhat muffled/smudged sound.

    ... Of course, nearly everyone makes these mistakes, because even home theater and PC enthusiasts tend to think that like the screen or PC, higher quality components is all you actually need for better results... which is true only after you solve all the acoustic issues in your setup.
  • profundido
    Dear Tom,

    I have started my quest for the holy grail of htpc 2 years ago and have found it about a month ago. I set for myself the following requirements:

    -it must be 1 box that is able to handle ALL available media
    -it must be user friendly and relative dummy proof: no switching audio formats and settings in between movies, just press play and experience the magic (a typical non-tech minded person must be able to play it all)
    -it must serve as TV-VCR in it's highest possible quality
    -the audio quality must be at high end hifi quality in such a degree that if you play FLAC from it professional hifi dealers are blown away
    -video must be full-HD
    -it must be able to play current videogames fluent in full-hd res
    -it must be able to handle all bluray audioformats flawlessly including dts-hd, master and LPCM WITHOUT HAVING TO SET ANYTHING OR SWITCH ANYTHING in the settings of the htpc
    -it must appear and look like a receiver, not like a pc in the living room
    -the surround sound must meet THX reference standards and volume

    my quest led me through (funny) the exact same products and their respective problems among many others. I was able just like you to get the digital passthrough to work with the Xonar 1.3 deluxe but with that card a few problems remain such as having to switch standards before playing it in the Xonar console, malformed LPCM that sounds flattened and lacking bass etc and last but not least the very slow hdmi-video switching of all Onkyo receivers so that wasn't perfect. Then I went to a hi end hifi seminar and listened to the professional audiocard of Onkyo and was totally blown away by the amazing crystal clear sound quality it produces in combination with a proper receiver that amplifies the channels seperately in a fully analogue way. That's when the light hit me. I rebuilt my entire htpc concept around this "analogue" setup and left the trail of the "immature hdmi" path. The result was amazing. 1 time calibration with the aid of Vista Ultimate built-in room correction and I was in the middle of the best htpc experience I had ever witnessed. I'm so happy with the result since it meets all the criteria of the holy grail. I also store and stream bluray content in full size on a 6.5TB windows drive at the speed of full gigabit (RAID 8*1TB) and play it with Arcsoft TMT 3. High dev TV functionality is provided with Firedtv, an austrian solution that allows digital satellite HD streams to be displayed directly on the pc with a modified version of DVB viewer as software (more userfriendly). For the analog amplification And all that in a fusion remote case from Antec é voila, there's your holy grail in a slim slick box ;)
  • profundido
    correction of missing part in above reply: For the analogue amplification of all 7.1 channels at THX ultraplus 2 standards and the volume of dolby reference I use the Onkyo 906 networkreceiver with 200watt per channel. Once the setup is calibrated, nothing else has to be done or switched on the receiver except volume control.
  • swt_2k
    Great information in this article "The HTPC / Windows 7 Chronicles: You Asked, We Answer!”

    Like most Media Center software users, I wanting to see a Digital PCI tuner card certify by Cablelabs; I don’t like to set top cable box. By-the-way, you cannot find the "ATI TV Wonder Digital Cable Tuner" anywhere. Sony no long lists that item. Also that item only uses the 1.0 unidirectional cable cards as opposed to the new 2.0 bi directional cable cards. Cablelabs is too slow bringing a digital cable card solution to the market.

    Does any know when or where I can buy a digital tuner like the ones in current LCD TVs?

  • Shadow703793
    Not sure if this was out when this was written, but there are PASSIVELY cooled 4670s. For example: