Dolby TrueHD and DTS-HD Master Audio via Tos HD-XA2 - High-Def Digest Forums
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Old 05-07-2007, 08:23 PM
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Default Dolby TrueHD and DTS-HD Master Audio via Tos HD-XA2

I was reading the review on the XA2 on the highdefdigest website, and it was confusing how it decoded Dolby TrueHD. Does it internally decode it and pass it on as an Uncompressed PCM track, or can it output it as a Dolby TrueHD bitstream. I would really like to know since this is the one reason on whether or not I get a new receiver or not, and whether or not it is worth it to go buy a high end HD DVD player for the HDMI 1.3 feature, because if it can't output TrueHD as a bitstream, there's no difference in that and the A2, but for $300 less.

Last edited by dajohn29; 05-07-2007 at 08:26 PM.
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Old 05-07-2007, 09:42 PM
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The Theory is the XA2 does both "internally decode it and pass it on as an Uncompressed PCM track, or can output it as a Dolby TrueHD bitstream". For dts-HDMA that one will require a Firmware update to enable it at some point.

I say "theory" because things get a bit complicated for passing Raw bitstream via HDMI 1.3 from the XA2. It has to do with how the Disc is mastered at that point.

*EDIT:
http://www.avsforum.com/avs-vb/showt...&&#post9571020
Quote:
"Advanced content" for audio means the disc was authored in the expectation the player would implement the mixing of audio in various ways before sending it to the outputs. This includes sound effects for overlayed menus, sound mixing for comment tracks, alternate languages based on just switching out the center channel, etc.

Encoded audio formats have to be decoded before mixing can happen. Mixing can't happen in the AVR because the AVR doesn't see the multiple tracks of mixable audio coming off the disc and also doesn't see the user interface commands that turn features on and off during playback or the control commands built-in to the disc that do the same.

The rules, then, are that if the disc is identified as authored for "advanced content" the player has to do any decoding of the new format audio tracks -- even if the viewer doesn't actually happen to be using any of those user-selectable "advanced" features at the moment. If a player can't decode a particular audio track from an "advanced content" disc, then it can't play that track. It might very well play the lower quality "core" track if one is present, or it will have to use a different track that it CAN decode.

If players don't follow the rules then it is not quite clear what will happen as the authoring tools the studios are using are designed and tested assuming players do what they are supposed to do.

Furthermore, this audio mixing is part of the user experience the studios design into each disc. The studios have been assured players will present their discs to viewers the way the studios intend them to look and sound. The studios are not likely to be happy if the industry says their "advanced" discs will play "correctly" only some of the time on some of the players.

So far, every industry pundit who has opined on this seems to agree that "advanced content" discs will drive "basic" discs from the market -- at least as regards traditional movies. This has already happened with HD-DVD, and is expected to happen as soon as this summer with Blue Ray -- even to the extent of existing, "basic" Blue Ray discs being rapidly re-released as "advanced" discs.

And from its standard DVD experience, the industry knows full well that most customers assume the "best" DVD version of any given movie must be the one that ships with the most extras and doodads. The Blue Ray guys, for example, are already assuming customers will buy the same movie AGAIN when it is available as an "advanced" disc.
Short version is HD DVD is going to do the decoding in the Player weather we like it or not. Now this isn't to say this won't be altered but who's to know what's going to happen on the horizon.

Ok back to the original post:
So, I think the main key is if you have a 1080p TV or not and if so, is Upscaning SD DVDs a big priority.

The sound output by all 5 Toshibas (A1,XA1,A2,A20,XA2) will be equal as all 5 internally decodes the TrueHD to PCM and outputs it via HDMI to your reciever. Confusing? Yeah a bit. I'll try to dig up a bit more info.

Last edited by Ohgami; 05-07-2007 at 10:45 PM.
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Old 05-07-2007, 11:46 PM
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I really do not like that one bit. I want to have the option also that if the movie was encoded with TrueHD and I do not want the player to "decode" it. I want it to be able to send the raw stream for decoding at the receiver level. Because if that is the case. What is the point in having TrueHD DD+ or even DTS-HD since everythng is geting output as LPCM.

P.S. In my opinion this is probably why maybe Universal does not include that many Dolby TrueHD sound option since is just comming out as PCM..........anyway that is just wrong.

Last edited by casper77; 05-07-2007 at 11:48 PM.
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Old 05-07-2007, 11:49 PM
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Hi,
just got off the phone with my friend, he has the XA2 and has confirmed that audio coming out of the HDMI port is PCM, whether it be TrueHD, DD+. This REALLY SUCKS!!! Still, it would be better than the cheap 360 add on that i have now, only gettin TrueHD at DD, WTF??? It sounds no different than the DVD version!!!
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Old 05-08-2007, 07:18 PM
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I thought it was common knowledge, that until the whole HDMI thing gets standardized, you need the HDDVD players with the 5.1 analog output to get TrueHD etc. in pure form. A1, XA1, XA2 etc.

Honestly I'd rather use the 5.1 analog outs over HDMI when it comes to movies.

I won't be upgrading my receiver for at least 2-3 years, when I buy a new HDDVD player (or whatever player has won by then) and whatever HDMI standard they settled on is well saturated into the marketplace.
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Old 05-08-2007, 08:01 PM
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By the way, I was wondering if PCM is digital or analog.
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Old 05-09-2007, 11:49 AM
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Quote:
Originally Posted by VC-1 View Post
I thought it was common knowledge, that until the whole HDMI thing gets standardized, you need the HDDVD players with the 5.1 analog output to get TrueHD etc. in pure form. A1, XA1, XA2 etc.
Incorrect, TrueHD is just compressed PCM (much like using winzip or winrar on a large file to save space). It is decoded in the player and sent by Analogs OR HDMI. So this means all Toshibas (A1,XA1,A2,A20,XA2) and the 1 RCA (HDV5000) output TrueHD as 5.1 PCM via HDMI. When TrueHD is output via Analog it is still being decoded by the player to PCM before it is sent to the Reciever.

dts-HD MA will be done the same way the only exception is dts-HD MA has a Lossy (Much like the dts track on a SD DVD) track embedded in the dts-HD MA stream so that those who can't take any advantage of the MA track will get a HIGH Bitrate Lossy dts track.

Quote:
Originally Posted by dajohn29 View Post
By the way, I was wondering if PCM is digital or analog.
Digital.
http://en.wikipedia.org/wiki/PCM
Quote:
Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code.

Last edited by Ohgami; 05-09-2007 at 11:51 AM.
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Old 05-09-2007, 12:06 PM
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The sound is the same for both pcm and truehd I don't know why all,the fuss about pcm as sounds tracks are amazing. I don't even think dtshdma will sound any better than pcm and if it does you will have to have high end speakers to hear the difference. Have a good day!!!
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Old 05-09-2007, 12:55 PM
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Ohgami's right, there's NOTHING to be upset about here. TrueHD is just lossless compressed PCM, so having the player decode that to PCM for output to the receiver does not throw out audio data from the original TrueHD bitstream. It's all still there. That's also why HDMI 1.3 ports are not that big a deal, since HDMI 1.2 can handle multichannel PCM.
More info on that at AVS. i'd post a link, but the forum won't let me until i post 10 times. bah.
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Old 05-11-2007, 08:46 PM
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If you set up this test:
1) Have the player decode a Dolby TrueHD losses Disc, output it via PCM over HDMI to a receiver and the receiver does no post processing.
2) Have the player output raw Dolby TrueHD lossless bit stream straight off the DVD to a receiver over HDMI, Receiver decodes TrueHD, no post processing.

If you switch between the different tests, you will hear no difference what so ever! none! They will sound 100% identical.

The reason is that all Dolby TrueHD (and DTS-HD-MA) decoders use the exact same decompression algorithm. There is no interpretation done by the decoder. It is like how Ohgami put it, like WinZip. WinZip on my computer will produce the exact same file as it produces on your computer, bit for bit identical. Otherwise it wouldn't work.

Now you ask, why pay more money for another receiver if all Dolby/DTS chips are the same in all of them? Well, that's not what you are paying for. What you are buying are DSPs and DACs. Those are the chips that interpret your digital information and try to enhance it. And it makes no difference where the Dolby or DTS is decoded, whether in the player or receiver, because the DSPs only work on PCM.

The downside to decoding the bitstreams in the receiver is that you lose all the special features, like mixing two audio tracks into one. Even on the Dolby website it says how the player is responsible for decoding the Dolby TrueHD track and mixing it with a second audio commentary or even streaming audio off the internet.
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