Understanding 8-channel LPCM over HDMI: Why it Matters and Who Supports it
by Anand Lal Shimpi on September 17, 2008 2:00 PM EST- Posted in
- GPUs
The Fix: 8-Channel LPCM over HDMI
But, Wait! There is a solution. It's ok to send uncompressed audio over HDMI, so in theory you could decode TrueHD/DTS-HD audio tracks in software and send them out as decoded, uncompressed LPCM without a Protected Audio Path.
Cyberlink, everyone's favorite player software manufacturer, supports decoding both TrueHD and DTS-HD MA in software (although it appears that Cyberlink does downsample the 24-bit 48kHz LPCM output to 16-bit 48kHz, but at least you get 8 discrete channels even if you lose the bit-for-bit lossless accuracy of the original signal).
With software support and no protection requirements to worry about, all we need is basic hardware support - and here's where most companies have failed miserably over the past couple of years.
It takes a lot of bandwidth to send 8-channels of uncompressed, 24-bit, 48kHz audio to the HDMI display engine. In the early days, GPU makers simply passed along SPDIF, which only offered 1.5Mbps - enough for 5.1 Dolby Digital, 5.1 DTS, or 2-channel LPCM to be sent over HDMI.
Intel guessed right enough to include a wide enough bus on its chipsets between the audio codec and the HDMI output engine to support up to 8-channel LPCM. NVIDIA eventually followed suit with its GeForce 8200 series of IGPs, while AMD is still lacking support for anything above 2-channel LPCM (although all three platforms can give you 5.1-channel DD/DTS over HDMI).
AMD has redeemed itself by being the first standalone GPU maker to offer 8-channel LPCM output over HDMI on discrete graphics cards with the RV7xx series of GPUs.
The Realtek codec in the Radeon HD 4800 series GPUs supports 8-channel LPCM over HDMI
Selecting 8-channel DTS HD MA in Rambo on Blu-ray
8-channel LPCM from the Radeon HD 4850 to an Integra DTC-9.8
It works!
Despite supporting 8-channel LPCM, the G45 still lacks a truly protected audio path and thus will never be able to send an encoded Dolby Digital TrueHD or DTS-HD MA signal over HDMI. I suspect that its successor in 2009 will finally add this functionality.
Whew. There you go, that's what all of this 8-channel LPCM talk is all about. It’s supported on NVIDIA’s GeForce 8200/8300 chipsets, Intel’s G965/G35/G45, and AMD’s Radeon HD 4800 and 4600 series. Done.
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Anand Lal Shimpi - Thursday, September 18, 2008 - link
Actually I believe both TrueHD and DTS-HD MA include the lossy DD/DTS tracks as a part of their spec. If you can't decode the lossless version, it should default to the lossy version. This is how it works on CE devices but admittedly I haven't played with it enough on the PC side.Sigh, there's so much work to be done here :)
-A
jnmfox - Thursday, September 18, 2008 - link
True, on the PS3 you have to make sure you have LPCM selected as your output, but if the original poster has it hooked up properly than he should be getting the lossless version.That is also part of the problem, so many blasted formats. I understand what they are and why we have them but to the un-Home Theater educated, i.e. my parents, it is just a bunch of mumbo jumbo.
This is a time when the movie industry should be trying to make things simpler instead it is just getting more and more complicated and as we can see from the posts it turns a lot of people off. A lot of people that may have been paying customers.
There is a lot of work to be done and it is sad we are so far away.
jnmfox - Wednesday, September 17, 2008 - link
Obviously I don't know your set-up but if you have your PS3 set to transcode the audio to LPCM and have it hooked up to your AVR via HDMI then you should be getting a lossless audio track not a downsampled DD signal."but my HTPC has a much better quality picture due to GPU acceleration magic"
Are you talking about SD-DVD PQ or Blu-ray PQ?
The Blu-ray jukebox would be nice.
sprockkets - Wednesday, September 17, 2008 - link
This is 2000 all over again: trying to find a sound card that actually passed on a DD signal via spdif with a dvd software program that properly talked to said sound card was a PITA. Then VLC came out and ended all the BS with the a52 codec and it being a free program. I remember buying a $20 sound card and finally having the right WinDVD to work with DD, even if it was the analog ports. What sucks is they wanted $60 for the same stupid program separately.Of course, why bother using cyberlink and paying them $$$ for the program (the version bundled with blue ray drives is crippled) when you can buy...
fri2219 - Wednesday, September 17, 2008 - link
I fail to see what problem 8 channel audio solves, aside from "how do audio vendors sell more equipment?".Human brains are lousy sound locators, this just isn't needed- 6 channel audio is pushing it as it is.
When you factor in the fact that most people in the G8 under 40 have damaged their hearing, it's even nuttier.
sxr7171 - Monday, September 22, 2008 - link
Seriously, just like the megapixel race the number of channels race is simply moronic.fuzz - Thursday, September 25, 2008 - link
don't know if there's any racing going on. i don't think i've got a single movie (regardless of format) that does anything over 5.1ch..nilepez - Sunday, September 21, 2008 - link
I'm not sure about 7.1 (since virtually nothing is encoded at 7.1), but 6.1 provides a rear center, which can help with pans for people who aren't in the center of the room. 7.1 does the same thing, in theory, but I don't htink there's much advantage unless the movie is encoded that way.I"m actually a bit surprised that BD movies aren't encoded in 6.1 or 7.1
fuzz - Thursday, September 18, 2008 - link
true where audio is concerned, thats why nobody has made this a priority.. the point though is not that 8ch 24/192 is so much better than 6ch 16/48, rather that these ineffective and costly practices are in place when they shouldnt be..the fidelity argument is also largely true of HD video.. a waste of time if you don't own a HD projector and view on a 100" screen. you won't see sh*t-all difference between your DVD and a HD movie on a 32" display if you're sitting further than a meter away.
well okay you might if you *really* pay attention but then you'd be missing the movie ;)
npp - Wednesday, September 17, 2008 - link
You couldn't be more right.But people like big numers - well, 7.1 can't be worse than 5.1, right, just like megapixels, horse power, cores, and everything else.
This aside, I find the "bit perfect" hype to be the next stupid thing. In my eyes, it's simply that most people don't want to admit that their ears and brain are imperfect, and can be fooled (by means of frequency masking). The word "lossy" seems to be a bad one, but I've heard plenty of "lossy" sound that was better than studio-mastered CD-s... And a lot, yes I mean A LOT of people can't hear any difference between properly compressed and uncompressed tracks at all... And yes, human hearing degrades rapidly with time, to a point when even a 10 Khz sound can't be heard - but you can rest assured that you have all your frequencies up to 48 Khz untouched, it's lossless.
You just have to swallow your ego to admit this, and there are plenty of people who aren't prepared to do it. You have the guys at stereophile.com which can hear not only differences between cables, but also between their wall sockets, ladies and gentlemen. A separate power line gave an amplifier something like more vivid and punching sound, for example.
I don't know who is crazy in this case but I think that people got what they needed long time ago and anything beyound that (read: all the 24bit/192Khz, 7.1, etc. stuff) provokes more imaginative than objective, quantitative effects... And of course you'll hear a difference if you've paid an amount enough to feed a small african village just for equipment, you have to.