6.1 with a 5.1 receiver?

[rcchap]

I just recently purchased a new center channel for my ht. I now have an extra center channel. Is there any way that I can use this extra speaker as a rear center with only having a 5 ch receiver. My current setup sounds great and I would hate to mess it up but on the other hand I hate seing it go to waste and if it could help round out the soundstage that would be great. I've got 6 pre outs on my dvd player but I don't have the cash for a new amp :cry: .
Thanks for your help.
Chris

[Gordon Moore]

Yes It CAN be done....you need to find an old reciever with Dolby Prologic (try a pawn shop or garage sale...you can likely find one for $50 or less ....I'm sure you can scrounge up $35 or so and do a little looking around)

Here's the instructions:

http://www.soundandvisionmag.com/article.asp?article_id=425&section_id=2&page_number=1

Have Fun!

[rcchap]

Thanks Gordon. That was exactly what I was looking for.

Chris

[Shane Martin]

You could also get a Circle Surround Decoder which can simulate EX as well. CS6.1 is what it is called. My friend uses one.

[purplepeople]

Or you can take the left/right surround pre-outs from your 5.1 receiver and plug them into ANY stereo amp/receiver with a mono switch. The speaker outputs on the second amp now both output both center surround.

ensen.

[Gordon Moore]

Jensen, I'm missing how that solution works :scratchhead: It's Friday and I've been in a fog ALL DAY :lol:

Wouldn't you still need an algorithm to matrix out the rear center? Simply changing a stereo signal to mono would only net you a mono left/right surround channel in one speaker, I don't think it's going to be enough to get it done.


Gordo

[Gordon Moore]

You could also get a Circle Surround Decoder which can simulate EX as well.

On the cheap? That would be another workable solution though.

[Shane Martin]

On the cheap?

Not really. They were $200 or so. You might be able to get one dirt cheap on ebay I don't know.

Wouldn't you still need an algorithm to matrix out the rear center?

Yes which is why the solution doesn't work.

[Cracking Oboe]

Hi Purplepeople eaters, :rofl:

I think I understand how Jensen' solution would work. The L&R surround preouts would be split immediately with one L/R pair sent to your surround channel amps as usual, and the other L/R pair to a stereo amplifier/reciever. The stereo reciever could combine the two channels via the mono switch. You would end up with two center back channels with the combined the L/R surround signals available for use from the old 2 ch reciever. (rather than the matrixed L/R surround and back channel from the pro logic reciever solution). The prologic receiver would require preouts if you wanted to power your L/R surround channels with an outboard 5-ch amp with the Sound and Vision solution!

Cracking!

[purplepeople]

Center surround isn't even encoded. It is merely the sum of the left surround and right surround signals. LS + RS = CS. This is why a Pro-Logic decoder will create it.

My solution requires the new mono'ed center surround channel to be set to a level of -3dB (as the sum of the LS and RS channels yields double the signal strength). This won't be a problem if you set the levels with a noise generator and a meter.

I personally feel it would have been better had they encoded the center surround channel as LS - RS and out of phase by 90 deg. This would be the way Pro-Logic decodes its rear channels. Doing this would have mean that instead of "anchoring" the EX surround channels behind the viewers, a distinct 6th channel of sound could actually be mastered into the mix.

Of course, as it stands, my solution allows the use of ANY amplifier that can mono any 2-channel input. You could pull the old 70's monster out of storage and use it for nice clean amplification.

ensen.

[Gordon Moore]

Center surround isn't even encoded. It is merely the sum of the left surround and right surround signals. LS + RS = CS. This is why a Pro-Logic decoder will create it.

Err, are you sure about that.... :scratchhead: Now I'm confused....
(maybe we're talking the same thing here and I'm not clueing in.... I realize that the Rear Center is matrix'd in the discrete SL and SR tracks which is why you need the ProLogic Processing (I thought) you you seem to say the there is no Out of Phase Center Back channel and that seems contradictory to Dolby's site and others that explain EX. My understanding the Center Back was similar to how Center Front was decoded through Pro-Logic... No?

Quote from Dolby themselves:

Feature films originally released in Dolby Digital Surround EX (the cinema version) carry the encoded extra surround channel in their subsequent DVD releases, as well as onto 5.1-channel digital satellite and TV broadcasts. If your home theater system has a receiver or preamp/processor with Dolby Digital EX decoding and speakers to support 6.1 or 7.1 playback, you can hear Surround EX soundtracks as they were meant to be heard, with the increased realism created by the extra surround channel. As in the cinema, with regular 5.1-channel Dolby Digital playback no sonic information is lost (although you'll miss out on the heightened realism).

Current Dolby Digital Surround EX soundtracks contain a digital flag that can automatically activate the EX decoding in a receiver or preamp/processor. For titles released prior to late 2001, however, you need to turn on the EX decoding manually.

AND....

http://www.geocities.com/Heartland/Park/6461/surroundex.html

6) How is Surround EX encoded onto a film soundtrack?



A discrete rear soundtrack is created for a film, and is then matrix-encoded into the existing discrete surround left and right channels. This is done by dividing equally the surround back channel signal and adding it to the left and right surround channels. This is the same method the center channel information is encoded in a Dolby Pro-Logic track. Dolby also specifies a phase shift in the left and right surround channel signals of +/- 45 degrees (rear information I assume added after the phase shift.)



7) How is Surround EX decoded?



A Surround EX decoder takes the discrete left and right surround channels and outputs left, back and right surround channels. The SA10, Dolby’s EX decoder for cinema theaters, uses “standard Dolby Pro-Logic in which the back surround channel (rear) is extracted in the same way the front (screen) center channel is derived form the two-channel Dolby Surround soundtrack.” WSR #32. Info that is in phase and equal in both l/r discrete channels is steered to the back channel. To ensure non-EX sounds (l/r surround effects) are not pulled into the back channel the l/r surround channels are encoded with a phase shift of +/- 45 degrees. This prevents full steering to the back surround (which would create a mono-blob type effect) and at the same time keeps the sound from being pulled to the “Extra” channel.



8) What is this ‘Extra’ channel?



Two matrixed channels can be derived from a two discrete channel mix. In Surround EX, one of those is the back surround channel (see above.) The other is known as the “Extra” channel. Currently Dolby/THX has expressed no definite plans for this channel.



9) Why are the left and right discrete rear channels phase shifted by +/- 45 degrees?



To ensure non-EX sounds (effects intended to only be reproduced by either the left or right rear speaker(s)) the l/r surround channels are encoded with a phase shift of +/- 45 degrees. This limits l/r surround information collapsing to the rear surround (which would create a rear mono-blob type effect), and also keeps the sound from being pulled to the “Extra” channel (which is phase shifted by +/- 90 degrees.) I would propose Dolby included the phase shift to offset the limitations of Dolby Pro-Logic which detects signal dominance to adjust output gain levels. I don’t foresee any apparent negative effects from the surround channels being phase shifted as this occurs in Pro-Logic and in a way with THX’s decorrelation effect

[purplepeople]

G: I think our memories are not serving us well here. My own recollection is as you had originally, that center surround is decoded the same as center front, which in Pro-Logic is played back as L+R without any phase shift. From what you found on the web, it seems that center surround is actually played back as L-R, the same a Pro-Logic rear channel.

So in your original suggestion the speaker should be hooked to one of the rear channels of the secondary receiver. In my solution, the secondary amp should remain in stereo and the speaker hooked up as follows: speaker pos to amp pos out left and speaker neg to amp pos out right and amp neg terminal not connected to anything.

Both these solutions still allow a 7.1 implementation. In yours, two available rear channels on the secondary receiver can be connected to a pair of rear center speakers. In mine, the hook up is as follows: amp pos left to rear center left pos, rear center left neg to rear center right pos, and rear center right neg to amp pos right, with amp neg terminals not connected.

To be honest, I am no longer sure how the rear centers are encoded (and thus decoded) and will have to really dig. Dolby doesn't seem to have the actual information available.. it may have to be dug up in an AES document or in something from Holman. I will report back when I confirm.

ensen.

[Chris D]

Well, we're getting a little confusing here. When you talk about 6.1, there are two ways it can be created/implemented:
1. A DISCRETE rear center channel for TRUE 6.1 channels (example: DTS ES Discrete)
2. A MATRIXED rear center channel from the left and right side channels (example: DTS ES Matrix)

The only way to truly create the first is to have a 6.1 receiver/processor, and play a 6.1 discrete encoded video source. I was watching Lord of the Rings the other night in DTS ES, and noticed that this is how that movie series has been encoded. So the rear channel is completely discrete as its own channel, having nothing to do with the side surrounds. (on a side note, I could not engage DPL IIx with DTS ES discrete to give me 7.1--this is one of the rare times you can't use it)

To get the second way of 6.1, you could also buy a 6.1 receiver, and now you can play 6.1 discrete encoded material, 6.1 MATRIXED encoded material (I think Terminator 2 is an example of this with DD EX) or play 5.1 material that uses a sound processing format that creates a new center rear channel from the side surrounds, like Circle Surround or DPLIIx. The other way of getting matrixed 6.1 sound is EXACTLY what Gordon wrote, using an old DPL receiver to take the decoded analog side surround signals from 5.1 audio and split them using DPL algorithms into left side, right side, and rear center channels.

[Chris D]

I'll just add one thing for the sake of clarity to be accurate with those that undertand processing more in depth, that may confuse more basic users. If it's confusing, disregard!

As I said, the only way to truly create a discrete rear center channel for true 6.1 channels is with a 6.1 receiver/processor and 6.1 discrete encoded audio. HOWEVER... using Gordon's technique of a 5.1 main receiver and a second old DPL receiver for the rear channels, you'll get something very close to 6.1 discrete. This is because 6.1 audio is backward compatible. If you play Dolby Digital EX or DTS ES (both 6.1 formats) on a 5.1 receiver, it will still be decoded and played as 5.1 audio. (in contrast, Dolby Digital is NOT backward compatible, so if you somehow sent a digital 5.1 signal to an old DPL receiver, it would not play) The way this happens is the rear center channel gets mixed into the side surrounds and is decoded by your 5.1 receiver. Then when you send the side channels to your analog DPL receiver inputs, it extracts the rear channel again and outputs thre three channels of left side, center, and right side. So because the center is matrixed in and then extracted, it's not truly discrete, but it'll sound close.

[ToddAnisman]

Hi guys..

I'll clear this up.

The "EX" channels on a 6.1 (which is delivered as a 5.1) are indeed matrixed. the box used to accomplish this is called a SEU4EX. We use them when mixing for EX encoded titles. I will say this- there is, to my knowledge, no commercially released film that is discrete 6.1 that is EX. It's just not done. when we are mixing for EX we actually have the chain in place, Ls-Cs-Rs --> SEU4EX-->Dolby SA-10 (Ex decoder)-->Ls-LsB-RsB-Rs.
In fact the Printmaster is done as such as well. the delivery is a 5.1 AC3 stream with the EX flag turned on.

-Todd A.

[purplepeople]

Okay, here's what I found...

Center surround channels are intended to be backward compatible with 5.1 playback systems. No surprise there.

What's important is that CS channels are meant to be played back as phantom center by a system with only LS and RS speakers, a matrix like that for front center channels.

That means that my senility is not yet upon me and the original hook-ups will work.... either use a second surround receiver and hook up the front 3 amps to the 3 rear speakers OR take the surround pre-outs to a mono-ed amp with one or two rear center speakers.

What's interesting is that unlike DD-EX, DTS-ES doesn't just matrix the CS signal into the LS-RS channels but uses extra bit depth to "switch" off (in a separate DSP codec) the crosstalk and phase distortion inherent in a matrixed signal.

ensen.

[Chris D]

Exactly. DD EX and DTS ES don't do things exactly the same.

[purplepeople]

To clarify, they can both be played back by any systems, whether it is 2.0, 2.1, 4.0, 5.1, 6.1 or 7.1.

You can only get the improved channel separation if you play DTS-ES material on a system that can decode it. Otherwise, DTS-ES or DD-EX software on a DD-EX 6.1 or 7.1 system is no better than the mods described above.

ensen.

[Gordon Moore]

Awesome Todd :T nice behind the scenes explanation. I take it you're in the biz?

Incidently Chris...myself, I'm not (or at least I thought I wasn't ) confused over the difference.

FYI....the only formats you'll hear in the theater is Dolby DD 6.1EX. No 6.1 discrete format exists from Dolby.

Out of the DTS camp DTS 6.1ES Matrix is the theater format.
DTS-6.1ES Discrete is a special hometheater remix.

As long as you can reproduce a Matrix'd 6.1 rear center in either DD or DTS you're as good as the theater presentation

Discrete just does not exist in the theater yet.


So as not confuse him with the technical stuff....just follow the Sound and Vision instructions and you'll get something very close to what a newer reciever can do inhierent with the DD 6.1 track on DVD's. Don't get hung up on the last 15 or so posts

[Andrew Pratt]

Discrete just does not exit in the theater yet.

It does from Sony's SDDS I believe

[Gordon Moore]

It does from Sony's SDDS I believe

Oops, you're absolutely correct ops:

8 channels of discrete, clear, crisp, vibrant digital sound.

http://www.sdds.com/

[ToddAnisman]

[QUOTE=Gordon Moore]Awesome Todd :T nice behind the scenes explanation. I take it you're in the biz?QUOTE]

Gordon-

Yes. I work for Technicolor Creative Services as a Re-Recording Mixer and sometimes engineer/installer. The same Technicolor as you see at the end of movies "Color by Technicolor"

here's something else to chew on-

Home Video releases widely vary from title to title in term of their quality. for example, the most common AC3 (Dolby Digital) Meta-data that you see on your DVD player reads like this:

3/2L 384kBps -27dB Dialog Normalization.

Guess what? that -27dB is almost always a wrong setting. sometimes you see -31, but that's still wrong. This is why people have the impression that DTS is so superior to DD- most people encode it wrong!!!!!

I'll make a very long and complicated explanation short-

every movie has a basic dialog level as mixed in the Dubbing theater. Star Wars has one level, saving Private Ryan has a different value. House of Sand and Fog A different value. It's just the level that it's mixed at, and can depend a bunch of different factors. when doing the encode for HV release, one is supposed to take a meter and measure the Dialog normalization value and then encode at that value. It could be -25, -20, 0r -30. It's almost never -27!!!. We have special meters that can measure this value over a given time period.

Here's what then happens in Dolby encoding:

A) All titles are turned down to a nominal level of -31dB dia norm. This is why so many DVD's seem "Quiet". Yes that menas that if you encode at -27dB it's turned down 4dB on playback.

B)there is compression built into the AC3 encoding. *IF* it's a hot movie and the dia Norm isn't set corrrectly, this can cause severe pumping or even distortion on the track. Listen to Armageddon for an example. This is because of protection llimiting in the Dolby process.

Ok, enough ranting. If you're interested, I'll be happpy to explain more, but I don't want to bore you right now (Plus I have a bowl of Pad Thai in front of me!!!!)

-Todd A.

[rcchap]

Thank you, thank you, thank you. You guys are the best. I've learned more about this subject than I ever would have guessed there was to know.
I love it and thanks again,
Chris

[Chris D]

Heheeee... yes, and thanks, Todd.

You're right... the current Armageddon available stinks. Still no anamorphic widescreen available on that title... WHAT???

[DelRay]

FWIW Chris, My last receiver was a Sony 444ES 5.1. I used the method described above to get 6.1. Luckly I had a old Sony pro logic laying around. This setup served me well. it really works. The only thing I did different was instead of using the prologic to power all 3 rear speakers. It just powered the center rear. The rear pre outs from my ES went to the CD input of the pro logic. But I still had the left and right surround speakers running off the ES. I figured the ES had better quality amps than the older Sony. Good luck.