5.1, 6.1, 7.1

Discussion in 'Speakers & Subwoofers' started by Jame pc, Jun 5, 2005.

  1. Jame pc

    Jame pc Agent

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    5.1= Front center, L front, R front, L rear, R rear, Sub

    6.1=?

    7.1=?

    Thanks!
     
  2. Niti

    Niti Extra

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    6.1 = 5.1 + center rear surround
    7.1 = 5.1 + left side (between front and rear) + right side (between front and rear)...
     
  3. Jame pc

    Jame pc Agent

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    Is a center rear used with sides ever?
     
  4. John Garcia

    John Garcia Executive Producer

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    6.1 and 7.1 are the same thing, as there is no 7.1 material in existence. 7.1 uses two rear centers, both of which play the same thing. The "side" surrounds in 6.1 and 7.1 are the "normal" surrounds in 5.1 and play the same information in each of the setups.

    There are 3 actual formats that are 6.1 - Dolby Digital EX, DTS-ES matrix and discrete. DTS-ES discrete is the ONLY true 6.1 format; DTS-ES matrix and DD-EX bot use a matrixed rear center.
     
  5. Jame pc

    Jame pc Agent

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    So 6.1 is front center, front L, front R, rear L, rear R, side L, side R, and sub? 7.1 adds another rear center?
    Thanks again.
     
  6. John Garcia

    John Garcia Executive Producer

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    5.1 has two rear surrounds. 6.1 adds one rear center to that and 7.1 has two.

    There are also various processing for 7.1 that alter the signal so the rear centers are slightly different based on the side they are on.
     
  7. drobbins

    drobbins Screenwriter

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    What is the point to the 7.1 then? Is it just hype to sell more speakers? If there were 7.1 material in the future, I wonder how much it would really add to the experience.
    It seems to me that it would be better to use two each of the R & L surround speakers than the center rear. This way you could correctly place the R & L surrounds for 2 rows of seats. I am thinking about trying this setup.
    Dave
     
  8. KenLeBlanc

    KenLeBlanc Stunt Coordinator

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  9. Jame pc

    Jame pc Agent

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    So in a 7.1 the right rear and left rear receive the same signal and the sides receive the different signals?
     
  10. SteveMetcalf

    SteveMetcalf Agent

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    7.1 was developed for theaters, where the rooms are typically longer. The second set of rear speakers recieve the same information as the first set of rear speakers. In a 6.1 situation the two rear-most speakers are matriced to produce the rear center information from the 6.1 encoding. Dolby 6.1 uses the rear channel information to derive the rear center content and DTS es(6.1)has separate channel encoding for the rear center speaker. On a 7.1 system the second set of surrounds also produces rear center information, when DTS is being played.
     
  11. Jame pc

    Jame pc Agent

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    So in 7.1, the sides are also called 1st set of rears, and the 2 rear centers are also called 2nd set of rears, correct?

    The Left Side and Left Rear receive the same signal while the Right Side and Right Rear receive the same signal OR with DTS the 1st rears are the rear channels while the 2nd rears are used for rear center... correct? Now I confused myself, maybe someone can interpret...

    Thanks again!
     
  12. John Garcia

    John Garcia Executive Producer

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    The rear centers are the same, DD or DTS. The confusion comes from the fact that all of them are called "rear", but that's sort of left over from when there were only the two rear channels. The distinguishing desc. now seems to be rear center or surround back.

    This pic that KenLeBlanc posted should sum it up:
    [​IMG]
     
  13. SteveMetcalf

    SteveMetcalf Agent

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    Good post John. The pic says it all. I would like to point out however, that there is a difference between dolby digital ex and dts es(6.1). Although with both formats the two rearmost speakers do act as a mono channel, with dolby this channel information is sent to the speaker by the reciever, not unlike original dolby surround. It takes the information which is common to the left and right rear speakers, and sends that to the rear center channel. Dts is better for two reasons. First the rear center is a separately encoded channel, so the mix engineer can determine what should be heard, and secondly the compression of information is less with the dts format.
    I wanted to mention this so that once jame pc gets his system up and running he can experience the best his system has to offer by using dts es whenever possible.

    Cheers!
     
  14. Jame pc

    Jame pc Agent

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    Just so my little mind can understand, there IS a difference in the left and right, correct (the Left Side and Left Rear receive the same signal while the Right Side and Right Rear receive another signal)?
     
  15. John S

    John S Producer

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    The two rear/back speakers recieve the same signal all other channels are descreet.

    Take a 6.1 AVR and put two speakers on the rear channel and you are more than 95% the way to as true of a 7.1 system as exists currently.


    There are obvious steering advantages for most of us that have tested the different configurations in our own environments.
     
  16. ChrisWiggles

    ChrisWiggles Producer

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    This has been discussed in depth, and first you have to differentiate between DTS-ES matrix, and DTS-ES discrete. The matrix version functions identically to DD-EX, using the same matrix encoding method. DTS-ES discrete carries a discrete rider version of the 6th channel, while ALSO using the same matrix version in the 5.1 portion of the mix for backwards compatibility. In theory, the discrete version should come out identical to the matrix version. Further, the mix engineer *does* determine what is in the mix in the matrixed form. The compression issue is very contentious between DTS and DD, and the DTS-ES discrete may be less desireable than DTS-ES matrix, because it has an extra discrete channel to which precious data must be dedicated.
     
  17. ChrisWiggles

    ChrisWiggles Producer

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  18. SteveMetcalf

    SteveMetcalf Agent

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    Quote:

    "Further, the mix engineer *does* determine what is in the mix in the matrixed form."

    Please tell me how the engineer does this without encoding. Until this year I was employed as a studio recording engineer. Although I have not mixed for surround, I have a good knowledge of what it is and how it works. I am curious as to how an engineer would be able to predict the behavior of the rear speaker as accurately as if it were encoded.
    What I know is this: Center channel matrix processes analyze the common information between channels. When mixing in a stereo application, you could have a sound that appears to come from the center, but is not phase coherent and would therefore not be sent to a matriced center. In this situation the sound woulod not be focused. In addition, certain stereo effects placed in the mix can be misplaced or lost in the matricing process. Such as assymetrical effects which use similar properties, but differ from left to right in order to make space for other sounds, or to create the illusion of space within the audio. These effects are signifiganly different from one another but at the same time have information that is common to the mono source. The information that was common will be sent to the center, even though it's supposed to be left or right, now you've lost some depth to your audio.
    On top of all this, you have variances in the processing to consider. Just like amplifiers differ in sound, I'm sure not every processor will act the same way.
    It's for these reasons I don't believe you can accurately predict what the rear center will do.

    I don't believe I know everything, (like I said I have never mixed surround sound) so please tell me if you disagree and why.

    Cheers!
     
  19. ChrisWiggles

    ChrisWiggles Producer

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    The mix is done in full discrete channels, then encoded matrix-style, then played back to test to make sure the intended discrete original is correctly reproduced when played back from the matrix variation. This is how it was often done in pro-logic days, an engineer would mix using 4 discrete channels, then it would be encoded into stereo using a PL encoder, then played back to test the intended effects. The same thing happens now, except the matrix encoding for a rear back is very simple and very predictable, so much less problems encountered as with older PL stuff. I don't even know if they test the playback anymore.

    Keep in mind that even with discrete delivery on a DTS-ES discrete track, the matrixing process is still the same for the 5.1 portion. Theoretically, the end result would also be identical, because the discrete 6th channel rider is also duplicated in the 5.1 mix matrix-style for backward compatibility. On ES-discrete capable systems, the discrete track (which is identical to that matrixed across the two surrounds) is used to cancel out that duplicate matrix version. So the two tracks are the same. Theoretically, in a matrix-only capable environment, that same track would be correctly decoded and sent to the rear and be identical to what is on the discrete rider that is not utilized.

    hope that helps explain!
     
  20. Parker Clack

    Parker Clack Schizophrenic Man
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    Chris:

    Correct me if I am wrong but it is my understanding that nothing is recorded in 6.1 or 7.1 anyway so the benefit is from "derived" information that is in the orginal mix anyway.

    With Logic7, THX Ultra 2, PLIIx they output an interprolation of the DD or DTS mix to achieve an apparant "fuller" sound out what was orginally recorded.

    Am I close hear or couldn't hit the a barn from 3 foot away with a shot gun?

    Parker
     

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