What is the difference between Matrixed and Discrete audio channels?

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Discrete means that you have a multi-channel soundtrack that is stored so that each of the tracks stays isolated from each of the other tracks, and you have true separation between all the channels.

Matrixed means that the multi-channels are blended together and stored not isolated from one another. In this case, instead of having each track available as a discrete audio stem- you have to pass the audio through a processor in order to turn it back into multi-channel.

Think of it this way:

Imagine you have 6 different colors of water you wanted to pipe from the water plant to your house. When they get to your house- they need to be separate and placed in special tanks, one for each color.

In a discrete system- each color would be routed from the plant to your house in individual pipes. The water would start out as 6 individual colors, would travel completely separate from one another - each on a dedicated pipe, and would arrive at your home on these 6 discrete pipes. You could then route each color to the appropriate tank, and have the pure 6 colors of water you started with at the plant.

In a matrixed system- the 6 colors water would be combined together and would travel in maybe only two pipes. They would be mixed together in a specific way at the plant- then they would travel down the pipes to your home, where a filter would try to sort them back out into the 6 original colors.

So, in the case of a matrixed system like Pro Logic- this takes 4 original stems of audio and blends them together into just 2 channels ("pipes"). At the other end, a pro logic processor (a filter)- tries to sort them back out into the 4 original stems they started with.

In the case of DD EX, which is a 6.1 channel system that has a matrixed rear center channel- it takes the rear 3 channel audio stems (Rear Left, Rear Right and Rear Center) and blends them together into the 2 available rear channel "pipes" (The front channels and the sub remain completely discrete) - and a EX processor can then sort them back out into the 3 original stems.

Dolby Digital EX basically takes 7 colors or water and passes them using only 6 pipes... using a filter at the other end to re-create that 7th color.

Which formats are which? What is DTS-ES? Is there a DD EX 6.1 discrete? How big of a difference does it make?

Dolby digital does not offer a discrete 6.1 format at this time. Their 5.1 system is a completely discrete audio format, and they simply added a 3rd rear channel (a rear center) using a matrix system as described above.

DTS offers BOTH a "discrete" 6.1 version called DTS-ES Discrete and a matrixed 6.1 version, which I believe they call just DTS-ES.

How big of a difference does it make? Well, to me, very little.

Although I personally saw Dolby's decision to make the rear center a "matrixed" channel as a step BACKWARDS- to be honest this type of matrixing is the easiest to do. Any time you have a stereo signal- it is very easy to find a "center" image within that signal. Simply analyze the stereo signal, and figure out what is being sent equally to both speakers- and boom, you have a "center" channel. For the most part, I would say that the difference between a matrixed 6.1 signal and a discrete 6.1 signal would be slight-- especially for rear channels.

Also, keep in mind that there are less than 20 discrete DTS-ES encoded titles on the market right now (I'd even guess less than a dozen, but don't quote me on that).

Having all decoding schemes available in your receiver is probably the ideal, just to make sure you can enjoy everything that is available- but if your processor doesn't do DTS-ES discrete 6.1, I wouldn't sweat it too much.

Also- another issue you might need to understand is the idea of the EX matrix type decoding. As I said above, in real basic terms a EX processor takes the 2 rear channels and analyzes the two signals, and figure out what is being sent equally to both speakers- and creates a "center" channel from that.

This process can be activated with or without specific EX encoding.

In other words, you could run EX processing on any 5.1 title, and chances are you'd get some sort of rear center channel activity. On many titles, it is equally good as any title specifically created for EX.

The truth is, as far as I can tell, dolby has no intention of redoing their system to create a discrete 6.1 system. Without getting too technical- the basic design of dolby digital audio encoding means that a discrete 6.1 system probably couldn't be backwards compatible to a 5.1 decoder, and new docoder systems would need to be designed.

So a theoretic Dolby Discrete 6.1 disc probably couldn't be played back on a current system- where DTS discrete titles are backward compatible and work with the regualar DTS decoder.

Since dolby seems to have no desire to do anything beyond the matrixed DD-EX 6.1, and the fact that Dolby is releasing 10 times as many 6.1 titles as DTS, it seems obvious that DD-EX will be here for a while.

Article written by Vince Maskeeper of www.musicianassist.com . Thanks also to www.HomeTheaterForum.com.

© Copyright 2002. All rights reserved. Reprinted by permission.

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