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Dolby 4.1


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#1 of 16 Spottedfeather

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Posted February 04 2013 - 05:47 PM

I'm watching Alien on blu-ray and noticed an audio that I've never heard of before. Dolby 4.1. From what I understand, this is supposed to be front left, front right, back left, back right, and subwoofer. But there seems to be a center channel as well. Why is there a center channel ? The 4.1 sounds fine, but I'm just wondering why there appears to be a center channel on a 4.1 mix.

#2 of 16 Jim Mcc

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Posted February 04 2013 - 06:17 PM

How does it "appear" to be a center channel? I assume your receiver is set to "none" or "phantom" for the center channel speaker? This sends the center channel info to the left and right fronts, sounding like it's coming from the center.

#3 of 16 schan1269

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Posted February 04 2013 - 07:01 PM

4.1 soundtracks appear because the original soundtrack source wasn't good enough to go back and create 5.1. 4.1 is really DPL + .1. I would be shocked if there is an actual stereo surround. The Alien 4.1 soundtrack has been talked about since it hit Blu Ray. There are other movies as well. The reason "you have center" is because 4.1 means the rear channel is mono.

#4 of 16 Spottedfeather

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Posted February 04 2013 - 07:03 PM

No. My center channel is on. Set to Small. I thought that 4.1 was, as I said, the two front speakers, the two rear speakers, and the subwoofer. But if I turn my center speaker down, I don't hear any of the voices. My receiver doesn't have any Phantom setting. It's an Onkyo R391. Would the movie sound better if I turned my center channel off ? But if the movie is 4.1, why is it sending any audio to the center speaker ?

#5 of 16 Spottedfeather

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Posted February 04 2013 - 07:05 PM

4.1 soundtracks appear because the original soundtrack source wasn't good enough to go back and create 5.1. 4.1 is really DPL + .1. I would be shocked if there is an actual stereo surround. The Alien 4.1 soundtrack has been talked about since it hit Blu Ray. There are other movies as well. The reason "you have center" is that you aren't using "Direct" as the sound mode.

What should I have my receiver set on to watch a 4.1 movie ? When the movie started, it picked "Dolby D" mode, which appears to send audio to the center speaker for some reason. Won't Direct mode take away any processing ?

#6 of 16 schan1269

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Posted February 04 2013 - 07:06 PM

I edited my prior post, cause I had it backwards. 4.1 means the rear channel is mono.

#7 of 16 Al.Anderson

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Posted February 04 2013 - 11:25 PM

There are other movies as well. The reason "you have center" is because 4.1 means the rear channel is mono.

It took me a bit to figure out what Sam meant, so I'm posting it - the 3rd and 4th channels are the front and rear, not the L and right surrounds as you might initially expect.

#8 of 16 Spottedfeather

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Posted February 13 2013 - 06:20 PM

Would you listen to a 4.1 track with Pro Logic II ? When I watched the first Alien movie, it started in a listening mode called, I think, Dolby. It seemed to sound alright, but should I be watching these 4.1 tracks in Pro Logic ?

#9 of 16 schan1269

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Posted February 13 2013 - 06:28 PM

Use whatever sound mode you want... I would "assume" that if "direct" were used...the AVR would split the rear mono track in two...cause you don't have 1 rear speaker. I did "some extra research" on 4.1 the other day... It is, essentially, DPL with a separate .1...(If you remember back to VHS, there was no .1) So..."Direct" is already DPL... So the guess here... DD plays it as 4.1 with split rear with bass management. DPL ii plays it exactly the same. Direct plays it "like" DD, but without the bass management... TV Logic playes it decoded using "old" DPL.

#10 of 16 Lord Dalek

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Posted February 14 2013 - 04:50 AM

4.1 is not the same thing as Pro-logic. The channels are encoded as discrete and separate channels and nothing is matrixed in like a standard 2.0 surround track. This is because 4.1 is basically the old 70mm Dolby format which basically eschewed the center-left and center-right for a pair of duplicated bass channels (the .1). The three remaining channels and the mono rear were encoded separately as mag stripes and that's where you get 4.1 from (eventually the technicians at Dolby discovered they were wasting an extra track duplicating the LFE information when they could use it for a second surround and that's how the modern 5.1 format came to be in 1979).


Most companies usually do some level of stereoizing to the rears of these mono surround tracks to create 5.1 but Fox is one of the few that offers the original when available.



#11 of 16 schan1269

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Posted February 14 2013 - 05:05 AM

I wasn't refering to "source from the film"... From what I read...4.1 can be "brought out of" the matrix DPL tracks(if that is all there is to work with). Did I read up on where they got the 4.1 for Alien? No. 3.1 surround exists as well for the same reason. IF that is all that existed in the original film, great. But if that didn't exist, they used the matrix 2.0 to come up with it. Different ways to accomplish the same thing...go back to the original film...or use the "pre-done for VHS" audio transfer.

#12 of 16 Spottedfeather

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Posted February 14 2013 - 05:52 AM

After I wrote my first note, I tried some stuff with Aliens. It starts in a mode that is shown as Dolby. I tried other modes, but PLII wasn't one of the them. Which is alright, as long as I can watch the movie with the correct audio. I was just confused, as I had never heard of 4.1 Dolby before.

#13 of 16 JOHNnNM

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Posted March 06 2013 - 07:20 AM

Interesting.... Do 4.1 titles, offer the original 2 channel as well? Would prove a very interesting comparison. The 2 channel, "ProLogic" Laserdisc I have is actually a pretty impressive surround title for it's day. I just happen to watch it recently.

#14 of 16 Spottedfeather

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Posted March 06 2013 - 08:45 AM

For Alien and Aliens, the 4.1 is the original audio...as far as I know...

#15 of 16 Bryan Tuck

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Posted Today, 05:07 PM

Thought I'd bump this topic up, as I was trying to watch Alien with the 4.1, and I can't seem to get it output properly. I have a Sony STR-DN840 receiver and Pioneer BS22 speakers.

 

On ProLogic II, the surround channel goes only to the Left Surround speaker (Right Surround is silent). Same for "Auto Format Direct." On "HD Digital Cinema Sound," it comes through both surround speakers, but there is some definite stereoization going on. Does anyone know if there's a way to get the surround channel to play as dual mono from both surround speakers?

 

Is there a setting on the Blu-ray player I should look for? Thanks for any help anyone can give.


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#16 of 16 GregK

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Posted Today, 07:20 PM

I'm watching Alien on blu-ray and noticed an audio that I've never heard of before. Dolby 4.1. From what I understand, this is supposed to be front left, front right, back left, back right, and subwoofer. But there seems to be a center channel as well. Why is there a center channel ? The 4.1 sounds fine, but I'm just wondering why there appears to be a center channel on a 4.1 mix.

 

This has been for the most part answered, but as far as your receiver's readout is concerned, that is a function of Dolby Channel metadata. Some 4.0 mixes are dropped into a 5.1 template and while showing as "5.1", still may really be 4.0 or 4.1 soundmixes. 

 

Dolby's metadata channel options are quite various, and a few of the channel variants have made it to home video over the years. For example, some of the Universal Sensurround soundmixes were encoded onto DVD as Dolby 1.1 (mono channel with LFE channel) as sometimes that was the case for the original Sensurround mix.  For the DVD release of IT CAME FROM OUTER SPACE, a Dolby 3.0 track accurately conveys the original Left, Center, Right discrete mix.  And unlike older stereo pro-logic encoded mixdowns, Dolby Digital and Dolby TrueHD 3.0 and 4.0 mixes remain discrete.

 

DTS also has channel mapping metadata, but I've heard some of their variants may not be fully backwards compatible with some older decoding gear. Reportedly this is why the Sensurround encoded bluray of BATTLESTAR GALACTICA was encoded as 5.1, but really is a left/right front mix with an LFE channel. Outside of not properly redirecting the fronts to the center channel (a mastering error), it still gets the job done.

 

Your initial confusion over the 4.0 format is somewhat understandable, as there have been two types of 4.0 formats over the years:

 

3/1 indicates three front channels and one surround channel which is spread to multiple speakers. This is the common channel layout of Warnerphonic and Cinemascope and essentially all discrete 4.0 film mixes following.

 

2/2 indicates a quadraphonic arrangement, where there is no center channel, but the rear surrounds are split. The quadraphonic wave used this channel assignment, as well as some current multi-channel mixes.

 

Dolby supports both channel assignments in their metadata mapping.






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