What happens to 7.1 LPCM tracks on a 5.1 system - AVS Forum

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jshigashi's Avatar jshigashi
02:25 PM Liked: 10
post #1 of 14
01-30-2008 | Posts: 201
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I have sort of become the unofficial geek for my friends regarding home theater. Anyhow I am setting my friend up on a system and he is trying to decide if he wants to go for a 7.1 system. I told him that as far as movies (blu-ray of course) go they are few and far between, and he won't be able to get at least half of those that are out (PS3 / DTS-MA problem)... but who knows what the future holds.

Anyhow, I obviously informed him about lossless audio and he is going to go with a receiver capable of accepting all formats, but he asked me what would happen in the instances of the 7.1 LPCM tracks. Would he be able to select that and get 5.1 LPCM, or does he have to go with the 5.1 DD track.
Jiffylush's Avatar Jiffylush
02:31 PM Liked: 11
post #2 of 14
01-30-2008 | Posts: 4,027
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Quote:
Originally Posted by jshigashi View Post

I have sort of become the unofficial geek for my friends regarding home theater. Anyhow I am setting my friend up on a system and he is trying to decide if he wants to go for a 7.1 system. I told him that as far as movies (blu-ray of course) go they are few and far between, and he won't be able to get at least half of those that are out (PS3 / DTS-MA problem)... but who knows what the future holds.

Anyhow, I obviously informed him about lossless audio and he is going to go with a receiver capable of accepting all formats, but he asked me what would happen in the instances of the 7.1 LPCM tracks. Would he be able to select that and get 5.1 LPCM, or does he have to go with the 5.1 DD track.

When you select 7.1 and you don't have a receiver that uses it, or you only have 5.1 speakers you will get 5.1 LPCM.

I am not sure if you lose 2 channels or if they are just matrixed in the rears, but you do get 5.1 LPCM (I verified on Waiting... IIRC)
jshigashi's Avatar jshigashi
02:50 PM Liked: 10
post #3 of 14
01-30-2008 | Posts: 201
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Quote:
Originally Posted by Jiffylush View Post

I am not sure if you lose 2 channels or if they are just matrixed in the rears, but you do get 5.1 LPCM (I verified on Waiting... IIRC)

I guess that's what I am asking... do you lose the 2 channels? I just watched 3:10 to Yuma and I heard quite a bit coming out of the 4 surround and rears on my 7.1 set-up, just wondering if it gets the rears (mixed/combined/matixed?) by the receiver (Onkyo 605). If not it seems like it would be losing a lot. Not really an issue now so much, but could be in the future?
sdurani's Avatar sdurani
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Depends on how the soundtrack is delivered on the disc.

If it is an uncompressed PCM track, then who knows. I haven't seen a firm answer one way or the other as to whether the 2 surround-back channels are downmixed into the surround-channels or simply tossed away. It would likely be player dependent.

If the soundtrack is encoded in one of the new lossy or lossless codecs, then you will get all 7.1 channels of information in 5.1 channels, with none of the audio discarded. One of the advantages of using coded soundtracks is that they're designed to be backwards compatible with 5.1-speaker systems.

Sanjay
Doug Schiller's Avatar Doug Schiller
05:47 PM Liked: 21
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01-30-2008 | Posts: 1,185
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The odd thing, 7.1 PCM is the only soundtrack that my 7.1 system properly decodes.
DTS 7.1 (New Line) downgrades to DTS Core 5.1 and I don't think there has been a Dolby soundtrack that has supported more than 5.1 channels (not counted the on life support EX but that is really a matrixed deal).
oblio98's Avatar oblio98
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01-30-2008 | Posts: 367
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According to Alexander Jero who produces music in DTS Master Audio 7.1, he has the option at the encoding process as to how the 7.1 mix will be downmixed into 5.1. This is done in the decoder and keeps all audio information so that nothing is lost by not having the extra two speakers.

I would assume that Dolby TrueHD has the same capability.
Fanboyz's Avatar Fanboyz
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01-30-2008 | Posts: 2,431
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Question: I cant figure out if 7.1 sound tracks are really just 6.1 with the rears in mono.
Crank and the other films like Ultimate Avengers are this way.
However PS3 games like Resistance Fall of Man, are true 7.1 .
tai4de2's Avatar tai4de2
07:30 PM Liked: 10
post #8 of 14
01-30-2008 | Posts: 618
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Quote:
Originally Posted by sdurani View Post

Depends on how the soundtrack is delivered on the disc.

If it is an uncompressed PCM track, then who knows. I haven't seen a firm answer one way or the other as to whether the 2 surround-back channels are downmixed into the surround-channels or simply tossed away. It would likely be player dependent.

Player-dependent or receiver-dependent?

Is there a protocol negotiation such that the player knows that the receiver is only capable of 5.1 over PCM instead of 7.1, and therefore the player can react by performing some mixing? At least the latter part of that seems unlikely to me.
Fanboyz's Avatar Fanboyz
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post #9 of 14
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EDID data in HDMI tells machines what channels they have.
sdurani's Avatar sdurani
11:50 PM Liked: 1020
post #10 of 14
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Quote:
Originally Posted by tai4de2 View Post

Player-dependent or receiver-dependent?

I guess where ever the downmix is occuring.
Quote:


Is there a protocol negotiation such that the player knows that the receiver is only capable of 5.1 over PCM instead of 7.1, and therefore the player can react by performing some mixing?

Yes, as Fanboyz said the EDID on the receiver will ask for however many channels it can accept. If that turns out to be 5.1, then the player will send only 5.1 channels. If your receiver can accept 7.1 channels, even if it configured for 5.1 speakers (or even 2 speakers, like a TV), then the player will send 7.1 channels and the downmixing should happen in the receiver.

Sanjay
shamus's Avatar shamus
12:12 AM Liked: 13
post #11 of 14
01-31-2008 | Posts: 6,254
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Quote:
Originally Posted by sdurani View Post

Depends on how the soundtrack is delivered on the disc.

If it is an uncompressed PCM track, then who knows. I haven't seen a firm answer one way or the other as to whether the 2 surround-back channels are downmixed into the surround-channels or simply tossed away. It would likely be player dependent.

I would think so. This stuff is so new to everyone, who knows what they missed.
With my limited audio ears, Im pretty sure the Panasonic bd10 does indeed place any info from the backs back into the sides.
sdurani's Avatar sdurani
12:01 PM Liked: 1020
post #12 of 14
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Quote:
Originally Posted by shamus View Post

This stuff is so new to everyone, who knows what they missed.

Indeed, check out both comments in the following post:

http://www.avsforum.com/avs-vb/showp...&postcount=119

Sanjay
jshigashi's Avatar jshigashi
01:40 PM Liked: 10
post #13 of 14
01-31-2008 | Posts: 201
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Thank you for all of the clarification Sanjay, and others as well.
Roger Dressler's Avatar Roger Dressler
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01-31-2008 | Posts: 8,967
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Quote:
Originally Posted by oblio98 View Post

According to Alexander Jero who produces music in DTS Master Audio 7.1, he has the option at the encoding process as to how the 7.1 mix will be downmixed into 5.1. This is done in the decoder and keeps all audio information so that nothing is lost by not having the extra two speakers.

I would assume that Dolby TrueHD has the same capability.

The downmix is done in the encoder in TrueHD (maybe the same in DTS, too). That way, a 5.1 player only has to decode 5.1, not 7.1 and perform downmixing.
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