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Will this work? DD 6.1 Idea

393 Views 6 Replies 6 Participants Last post by  Hugh Magoo
100 posts! Cool

I believe I read something about this once. For those DD 6.1 soundtracks that have the rear center matrixed in with the surrounds can I do the following? Send my rear pre-out to another reciever and decode it with dolby prologic. Will this work or is the encoding matrix different or am I on crack?
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I think I remember reading about someone using an old Dolby Pro Logic only receiver to do just that.


for a long write-up describing the use of two receivers with a HTPC.

A matrix DTS-ES or DD-EX soundtrack uses simple Dolby Pro Logic encoding to matrix a center channel into the rear surround pair. Use "3-channel logic" setting on the rear receiver to extract the center rear (which is the "front center" on the rear receiver).

The Audio forums have more detail about DD EX encoding..

Thanks Rgb, you confirmed what I had hoped.

What I am going to do is use the L/R surround pre-outs to the stereo in on my second receiver. Then I'll use dolby pro-logic 3 channel and hook only my rear center to this amp. This way I am not using this inferior amp for my surround info on non es/ex soundtracks. I'll post how I make out!

The rear center channel information is actually encoded via "matrix encoding" in the RR and LR channels. Technically this is the original "Dolby Surround 2.0" encoding - which had no center front channel and mono rear surround via two speakers. Most Dolby Pro-Logic receivers handle this mode OK - but Pro-Logic has the center front channel and discrete RR and LR. You can actually use either a Dolby Surround receiver or a Pro-Logic receiver.

The short version of how you make this work:

Dolby Surround receiver: Take the RR and LR low-level outputs of the DD5.1 receiver, and feed them in to a stereo input on the Dolby Surround receiver. Set the receiver for "Surround" mode and attach the rear center speaker to either "Rear Speaker" output.

Dolby Pro-Logic receiver: Take the DD5.1 channel low-level output for RR and LR and feed to a stereo input on the Pro-Logic receiver. Attach the rear center speaker to the center front speaker output. Set the receiver to "Pro-Logic" mode.

The "Dolby Surround" option is the one that most closely approximates real Dolby 6.1 EX - the matrix encoding for Pro-Logic is somewhat different. However, Dolby Surround receivers also rolled off low frequencies for compatibility with the limited frequency response surround speakers common back then - there was often no optional setting for "Large" or "Small" speakers like most 5.1 receivers today.

In my opinion, both these methods only approximate real Dolby 6.1 EX - with compromises such as two volume controls.

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Someone asked this question at AudioReview.com, he got an answer from a DD/Dts engineer. Here is the answer:

"First, it is not 6.1. It is 5.1+1. Marketing people use 6.1 to make it sound more impressive. Dts has the only 6.1 format available to consumers.

Now to the receiver. It is a terrible idea. There is no way to align the systems rear center channels without delay. There is no delay on the front channels of DPL, for which EX is based on. Unless your rear center speakers are exactly the same distance from the listening position as your fronts and sides, that is vital. If they are, delay is not critical.

The signal has to go through D/A conversion twice, and A/D once. This does audibly degrade the sound, and adds noise to the process. If the soundtrack was mastered at 20bit depth, then it is likely that the DPL D/A conversion would truncate it down to the typical 16-18 bit resolution found in in most DPL processing in receivers, pre Motorola 56004 chip

The steering can easily be overwhelmed in older receivers handling digitally discrete signals. This is were "offical" EX improves on the DPL process.

Do not get me wrong, a DPL receiver will extract a L+R signal. It just won't be as clear, or clean as the real EX process.


Hope this helps.
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hmm. I have all of this Pro-Logic stuff sitting in my bedroom in an Onkyo Receiver and speakers. However my Sony STR 845 receiver doesn't have low level outs for any but the SUB. My DVD player has discrete 5.1 outs, as well as my sound card on the HTPC. Any chance that these 5.1 outs could be used for this purpose?
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