Lesson 101 on DTS 6.1 ES Discrete
Just in case you were wondering what the hell this sound format is exactly.
Here's a brief description (which will probably confuse the crap out of you even
more so ..sorry :)
For some time now we've been enjoying 5.1 sound from Dolby and DTS on DVD. A few
years ago Lucas Inc. wanted to enhance 5.1 sound and so got a few industry folk together
and they came up with Dolby EX. The idea being that you take the 2 Surround channels
and make then into 3 Surround channels. Left Surround, Right Surround and
Surround Back.
(just like Dolby pro-logic does from 2 channel stereo to make a front left, right and
centre channels)
Lucas's Star Wars: the Phantom Menace was the first film released theatrically with a
Dolby EX soundtrack and since then 20 or so English spoken films have included a Dolby EX
soundtrack (Chicken Run, The Bone Collector and the new version of The Exorcist to name
just a few)
So now the latest and great home theatre trip is 6.1 surround sound.
The Dolby and THX version of this for home theatre is called THX Surround EX,
non THX versions are generally called just 6.1 Surround
In typical 5.1 setups this Surround Back channel information is feed straight into your
Left and Right surround speakers and it plays back perfectly normal [so is backward
compatible]. In a 6.1 setup where your processor can decode this information, it
extracts the Back channel from the left and right surrounds and feeds it to your Surround
Back speaker/s (the THX standard requires 2 Surround Back Speakers to prevent narrowing of
the surround sound fields, Yamaha's new flagship amp has only 1 Surround Back output as
it's they don't employ the THX side of things, but I hear it still sounds great)The end result of Dolby and THX's 6.1 matrix sound is really are
quite impressive with much better localisation of sound in the surrounds. (the Terminator
2 : UE THX trailer with arnie walking in from behind is awesome, he comes from right
behind you!!)
DTS decided to go one better than the Dolby and THX version
of 6.1 matrixed surround sound and offer 6 fully discrete sound tracks (plus LFE).
On a DTS track which is DTS 6.1 ES Discrete encoded you actually have two parts to
the digital bit stream.
The original 5.1 mix (with the surround Back info matrixed into the left and right
surround tracks ) and tailed onto the END of this 5.1 digital bit stream is the discrete
surround centre track bit stream. The idea behind this is so DTS decoders which
CAN NOT decode ALL 6.1 discrete channels instead pick up on the 5.1 part and ignore
the extra discrete Surround Back Channel. (this is also also for playback of DTS's
ES matrixed 6.1 sound, which is the same principles as Dolby EX, and in fact you can
engage THX surround EX on a DTS 6.1 ES "matrixed" track as at the end of the day
all the THX processing cares about is that it's receiving 5.1 audio tracks [with centre
surround matrixed info] to turn it into THX surround EX.
* interestingly to accommodate for the extra discrete Surround Back Channel the DTS 5.1
bit stream data is reduced slightly to "fit" the discrete Surround Back into the
754kpbs or 1509 kbps bit stream area. so "technically" this does mean a
slight compromise to the overall sound quality seeing as the main data area with 5.1 mix
is compressed a little more.
Now this is were it gets trickier. At the end of the
day there are 2 Surround Back Channels in a DTS 6.1 ES Discrete digital bit stream (one
being matrixed the other discrete). So what happens with the "matrixed"
centre surround info is that it's extracted from the let and right surrounds and PUT BACK
into the left and right surrounds, 3 dB lower and out of phase with each
other. This is so the matrixed Surround Back info can't be fully localised and
theoretically no sound is lost, creating a sound gap, in the main surrounds due to the
extraction/reinsertion. (surround info in a 2 channel stereo mix is initially encoded out
of phase so as Dolby Pro Logic Decoders can extract surround info easily, all what happens
with a DTS ES mix is essentially just the reverse of this technique)
The "discrete" Surround Back info is then sent straight to the surround Back
channel/s, and wa'la' you have 6.1 discrete sound and it leaves Surround EX for dead!
I'm now hooked!!
I hope that makes some sense.
Matt.G
DVDown Under..
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