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Definitive guide to surround sound decoding?

Discussion in 'AV Receivers & Amplifiers' started by Brogan, Sep 21, 2004.

  1. Brogan

    Brogan
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    This isn't the best forum for this topic but as there isn't a forum dedicated to decoding and it is related to AV amps, I figured it was about the best place for it.

    Basically I'm trying to understand all of the various different surround sound decoding formats there are.
    This came about because of a quick and simple test I did with LOTR TTT trying to determine whether it sounded better in DD or DTS.
    I was surprised to hear that there are major differences between the 2 formats (on this disc).

    I played the very first scene (about 2 minutes in) with Gandalf on the bridge as he strikes his staff to break it.
    In DD EX 5.1 there is music and a lot of sound effects coming from the 2 rears.
    In DTS ES 6.1 the only sound to be heard is a small crack after his staff strikes the bridge and nothing else.
    I did a bit of further checking and from the start of the film as the camera sweeps across the snow covered mountains, there is music coming from the rears in DD but absolutely nothing in DTS.

    I then proceeded to check some other discs to see if it was a DTS issue or specific to this movie/disc.
    So I tried Gladiator and it worked fine for both DD and DTS.
    One thing I did notice however is the encoding is different between the 2 discs but only for DTS.
    The following formats are displayed in the window for each movie/format:

    Gladiator DD: DDigital EX
    TTT DD: DDigital EX

    Gladiator DTS: DTS+Neo:6
    TTT DTS: DTS-ES Disc6.1

    So although both discs have DD and DTS-ES on the sleeve, it is in fact a different flavour of DTS-ES for each disc.

    pez kindly pointed me in the direction of this site: http://www.hometheaterhifi.com/volume_11_1/feature-prologic-iix-3-2004.html which explains some of the formats but it doesn't explain what the difference is between DTS+Neo:6 and DTS-ES Disc6.1.

    So does anyone have the definitive guide to surround sound decoding which lists all of the various formats and flavours and which will help me in trying to understand which format is the best for each particular disc I own?
    Or should I just let the amp do it automatically and have the rears set to Auto or have the rears (7.1) always switched on?
     
  2. pez

    pez
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    it depends on the quality of the mix ;)

    really, it does! i mean on the TTT disk the dts es 6.1 has a discreet rear channel that doesnt contain the musical score, just a few sound effects here and there, whereas if you run it in dolby ex and get your amp to give you the matrixed in rear surround channel then you get musical score through them (as i remember it in the cinema - at least thats what i think!), so its obvious that the DVD producers mixed the 2 slightly differently.

    what confuses me is that even though theres a matrixed in rear in the left and right surrounds on all DTS6.1discrete mixes, they appear to be different to each other, with the matrixed in mix (which i believe in hearing when i select DTS+PLIIxC on my denon 2805 with the dvd player having selected DTSES6.1discrete - obviously ive switched off the autoflagdetect to enable DTS+PLIIxC) sounding much fuller and more like the DolbyEX rear surround (which has a music score) than the dtsES6.1discrete decode option on my amp.

    im with you on being confused!

    as for gladiator showing NEO6 and TTT showing 6.1, its probably because gladiator doesnt have a discrete DTS ES 6.1 soundtrack, so your amp switches on the NEO6 circuitry to create a rear from the other channels, whereas TTT has a discrete DTS ES 6.1 soundtrack (although as has been discussed, its a bit spartan compared to its Dolby EX relative and DTS+PLIIx sibling).

    weirdness!

    when in doubt, leave the machine to decide which one to use, and then come in here if it doesnt sound right!

    pez
     
  3. BrianC

    BrianC
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    Pez, you've totally confused me, are you saying you or the amp is switching to the DSP mode(s) of Dolby Prologic IIx or Neo 6? As if thats the case I'm not surprised you are missing bits?
     
  4. Thunder

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    What is happening is that the TTT disc is mixed in DTS ES discrete 6.1 so has a dedicated surround back signal and the amp is recognising this and playing it as it was recorded. If you have the R2 version of Gladiator its mixed in DTS ES matrix rather than DTS ES discrete which the R1 version has. Because the recording on the R2 is matrixed rather than discrete your amp is not picking up the ES flag and is adding Neo 6 to create the surround back signal. When a signal is matrixed it usually takes info from the other channels to create the surround back signal which is why you are getting more music etc out of the surround backs with Dolby EX and DTS ES matrix mixes :thumbsup:
    The following is a list of formats as best as I can explain them :)

    Dolby Surround, applied to stereo soundtracks, extracts four matrixed channels; L C R S
    Dolby Prologic, refined version of above.
    Dolby Digital AC3 5.1, 6 discrete channels
    DTS 5.1, 6 discrete channels
    THX surround EX, the original matrixed 6.1 system and was debued with the Pantom Menace. Was licensed for about a year and only THX certified kit was allowed to have it. Although lots of manufactures came up with their own versions.
    Dolby Digital 5.1EX, Dolbys matrixed 6.1 system not always flagged on disc
    DTS ES matrix, DTS version of Dolby EX. again not always flagged.
    DTS ES discrete, true 7 channel 6.1 system
    Dolby prologicII, applied to stereo signals provides a full 6 channel 5.1 matrixed output.
    DTS neo 6, older version was DTS version of Dolby PLII, new version works in a similar way to Dolby PLIIx( can be applied to 5.1 recordings to create 7.1 output)
    Dolby prologic IIx, creates a 7.1 output from a stereo source or can be applied to Dolby 5.1 or 5.1EX recordings to create a stereo surround back output.
    DTS 96/24, high resolution 5.1 system designed primarily for music as an alternative to DVDA or SACD :smashin:
     
  5. pez

    pez
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    Brian, if i switch my amp to dts+pl2x then i hear more rear sound effects and music than if i just use DTSES 6.1discrete on my amp (in both scenarios the dvd player outputs the DTSES6.1discrete signal).

    all dts es 6.1 discrete tracks contain the rear surround channel matrixed in with the left and right surrounds, so if you use a matrix decoder on it you can here the matrixed in rear surround, and if you use the discrete decoder, you hear the discrete rear.

    theres a big discrepancy between the 2 on TTT.

    seeing as theres no discrete rear surround channel in cinema dts or dolby, im wondering how they created it for the home? i seem to remember music from the rears in my cinema, so id say you are getting a truer representation of the cinema from listening to the matrixed track (either in Dolby EX or DTS ES) on TTT than you are if you listen to the DTS ES 6.1 Discrete track.

    cool thing about pl2x is that it gives you stereo rear surrounds too!

    pez
     
  6. BrianC

    BrianC
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    Ahh, makes sense now! :)

    I'd also be interested in if they remixed TTT for the home or not, my gut feel says that they did, so what you are hearing without PLIIx is what they intended? How accurate does the sound field seem?
     
  7. sharper

    sharper
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    My brain hurts :confused:

    what should the amp be switched to for for what format. :lease:
     
  8. Thunder

    Thunder
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    You cant use Dolby pro logicIIx with DTS only with Dolby formats :thumbsup:
    Yes the Lord of the Rings series of films were mixed for the home as are most New line releases :)
     
  9. Brogan

    Brogan
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    Well after reading that site and my AX5 user manual, I'm not really any further on in understanding all of the formats.

    About the only thing I have discovered is that DTS ES Discrete is the only real 6.1 format, with a discrete rear mono channel and a true LFE channel.
    The rest all contain some matrix element, even THX Ultra 2 Cinema and Dolby Pro Logic IIx.

    I guess ultimately it's not really important anyway as, according to my amp handbook:
    "When you input a multichannel signal the decoding is done automatically so you cannot choose these modes.
    With these modes the receiver will automatically employ the format of the sound source (for example, Dolby Digital or DTS).
    With two channel sources these first four modes will create surround channels"


    "These modes" being THX Cinema, Dolby Digital Pro Logic II Movie, Dolby Digital Pro Logic and Neo:6 Cinema.

    I suppose it's only really of any relevance when inputting a 2 channel signal as you get from e.g. Sky+ and then you have the option of choosing a particular decoding format.

    P.S. I noticed this comment on the site about DTS ES Discrete:
    "There have been no Hollywood movies circulated with this type of soundtrack (it has never been used in the commercial systems), and precious few DVDs include a soundtrack remixed for DTS ES Discrete"
    What were the odds of me picking one of the few DVDs with that format to do my very first DD v DTS comparison :rolleyes: :laugh:
     
  10. Arcangel

    Arcangel
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    PLIIx can be applied to DTS tracks. ;) Although it's up to the manufacturer whether they choose to implement it or not.
     
  11. Brogan

    Brogan
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    Eh?!
    Now I'm more confused than ever. :confused:

    If the amp automtically selects the decoding format, as mine does, how can you force it to use DPLIIx for a DTS source?
    Surely if you input a DTS signal then the amp will automatically select the DTS decoder?
    That is definitely the case with my AX5, with no means of changing it.

    And what would be the point of doing that anyway?
    Surely a DTS source decoded with a DD decoder is just not going to sound right?
     
  12. Arcangel

    Arcangel
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    Dolby PLIIx works with either 2 Channel or 5.1 Channel sources and will create either 6.1 or 7.1 Channels. In some respects it works more like a Post Processing format as it adds to the existing source. A bit like THX Ultra2 Cinema or Music modes, they create 7.1 from a 5.1 source (either DD or DTS).

    You can't force DTS decoding on a DD 5.1 track and vice versa but if your amp has Dolby PLIIx it will add it's processing to give you surround back output. There are other modes around that work in a similar way, such as Lexicon's Logic 7, Denon's Widescreen 7.1 Mode etc etc.

    Your amp will automatically select the correct decoder for the format on the disc and then depending on what other modes your amp has, you can then process the signal further. Whether that be Dolby PLIIx, THX, Logic 7 etc etc.
     
  13. Thunder

    Thunder
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    Well you learn something every day cheers mate :smashin: I suppose I just assumed that because my Tag DP wont allow it that you cant do it, whats that saying about assumption :blush:
     

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