Dolby EX vs Dolby Pro Logic IIx

I can select either... They do seem different. I dare say that DPLIIx seems a little more 7.1-ish than EX which seems more 6.1-ish.

Did that even make sense?

The important question is whether Pro Logic IIx is designed to specifically detect the encoded rear channel information in an EX-encoded soundtrack, and steer it to the rears. Or is it just designed to spread a plain 5.1 soundtrack through 7.1 speakers?

As I understand it, IIx is designed to handle EX soundtracks, and is the preferred decode mode for 7.1 speakers for both 5.1 and EX content, but I've not seen any authoritative statement on that from Dolby, either in their IIx or EX FAQs.

Certainly using EX decode mode for a non-EX soundtrack is wrong. IIx is the correct choice for that.

Wrong??? I don't think there is a worng choice. I run EX over a lot of 5.1, performance is generally great. EX is post processing, I don't see it as wrong at all. Use it when you want.

Even DD EX can be configured for 7.1, but both rear speakers get the same content, where as DPLIIx provides unique signal to the rear speakers.

Yeah, some of the UI or remotes are of horrible design. In old days, they use to do user surveys and implement some good ideas, now I guess no one has time or budget for these and every company tries hard to cut costs. Many owner's manual are not easy to read either.

The former. When the PLIIx circuit detects correlated mono info in the surround channels, it sends those sounds to both rear speakers. In those instances it behaves like EX decoding, running both rear speakers as dual-mono, for localization directly behind the listener. The advantage with of course is that PLIIx can switch to stereo rears in order to image sounds that are intended to be heard behind the listener, but away from the centre line.
Write to Dolby directly; this way you get an authoritative statement from the horses mouth.
While PLIIx is preferable, I don't see how using EX decoding on non-EX sources is wrong. The only sounds that are extracted and sent to the speakers behind the listener are the ones that would have phantom imaged back there anyway.

Sanjay

The problem with using EX all the time is that it will collapse the surround field. What if the surround at a point is actually mono? It will collapse to the rear speakers, and you'll get nothing from the sides; quite a different effect from the imaging if it were coming from both sides. This is the same basic problem as things collapsing to the centre channel at the front. You lose the "surround" effect originally intended.

In an EX encoded film, phase differences between left and right surround are used to ensure that those channels aren't collapsed into the rear unwantedly.

Presumably if PLIIx does EX extraction, it does it in a more intelligent way than EX so as to not oversteer to the rears with non-EX material.

Keep in mind that certain source material can be encoded with an EX flag or PL2x flag..
Stereo back surrounds can significantly enhance the soundstage..
Thats why EX is usually available in an AVR that has DPL2x..
The user can select which mode delivers the desired end soundstage..

Also thats the value of DD PL2X..
As well as Logic 7 7.1 postprocessing found in some of the HK AVRs..

Is there such a thing ? ? ?

Ed

Only if 100% of the information in the L/R surround channels is correlated mono.
Then those specific sounds will be heard from behind you. Any surround informaton that isn't mono will remain at your sides. This is consistent with how those sounds would have phantom imaged when using only 2 surround speakers.
5.1-speaker set-ups tend to have the surrounds slightly rearward of the listening area, causing dual-mono content to image behind the listener, which is where EX decoding places them.

The same thing happens up front: play a mono CD using 2 speakers and everything will phantom image in the centre of the soundstage, which is where a matrix decoder would place those same sounds.
No, the small phase shift is to allow the mixing engineer the choice of placing mono content behind the listener or at the sides. Correlated mono sounds go to the rear speakers, decorrelated mono sounds remain at the sides.

Since stereo information isn't extracted by the EX decoder anyway (whether on an EX encoded soundtrack or not), it always stays at the sides and doesn't collapse to the rear. So it is perfectly fine to use EX decoding on regular 5.1 material.

Sanjay

Yes, but a phantom image sounds quite different to a single source. There's a far more spacious effect when the mono sound is coming from spread-out sources. In the case of mono surround, the surround was probably originally intended by the mixer to be a surround, not a rear effect. Maybe it wasn't, but you don't know.

By applying EX processing, you're getting something quite different from what the original mixing engineer would have heard.


Yes. But if he wasn't EX encoding, then you've gone and made the choice for him - all mono effects get forced to the rears, rather than being true surrounds, as they would have been in the cinema or in the mixing studio.

Maybe you enjoy that effect, and maybe it works well with some titles, but it's not authentic.

A phantom image sounds like a single source. That's why vocals sound like they're in the middle of the soundstage even without a centre speaker.
The mixer heard it on an array of speakers wrapped around the entire mixing stage. That result is not possible at home with 2 surround speakers unless you decorrelate the mono surround channel and use diffuse speakers (like dipoles). You're also talking about a special case which is quite rare these days: a soundtrack with a mono surround channel. For mono content that is part of stereo surround channels, which is the norm with modern movies, there will be left-right-rear imaging that will be consistent with EX decoding.
On a home 5.1 set-up, a mono surround channel is not going to wrap all the way around the listener like it does in the theatre. Mono sound coming from 2 surrounds would end up imaging in between those speakers, which would localize behind the listener, consistent with EX decoding.

Sanjay

You're correct here, but the point is that basically no 5.1 films have mono back surrounds. Using EX processing almost always yields pleasing results. There are some exceptions to this where the surrounds are actually in mono, and this dumps it to the rear and you have no coherency between the rear and the front, you just have the front, then a big hole to the sides, and then the rear. This is distracting and not desireable. But again, there is only one 5.1 film that I've ever run across and that is Last of the Mohicans. The mix is 5.1, but my guess is that they just use the original pro-logic mix as "5.1" so the rears are completely in mono.

I also think that Scratch may also be this way, but I forget I may be incorrect about that.

In any case, for those extremely rare instances where the surrounds are actually mono then I leave it as 5.1. But again, this is rare, and pretty much across the board I use EX processing for basically everything else because it usually always sounds better.

"Keep in mind that certain source material can be encoded with an EX flag or PL2x flag.."

I also ask, is there such a thing?

Isn't that tantamount to there being PLIIx encoded source material?

Come on - are you seriously telling me you can't tell the acoustic difference between a phantom image and the output from the centre speaker? The difference in width is obvious, even in the middle of a complex mix. In a proper surround music mix, it's possible to create quite different results by choosing which of the 3 front speakers are used to create centred vocals. If you can't detect this, then I'm not going to lend much credence to your insistence on there being no problem using EX all the time...

Dolby PLII Music mode acknowledges this and lets you adjust a "centre width" parameter to control the amount of use of the centre channel.

Haven't you fooled anyone into thinking that your centre speaker was on when it wasn't?
Not on my system: mono sounds image dead centre, with no smearing across the front soundstage. I have heard systems though where the L/R speakers were deliberately not toed in so that dialogue appeared wider. But that is a set up preference, not something inherent to phantom vs hard sounds.

Getting back to EX decoding: the surround field collapse you describe is something I've only experienced with soundtracks where the surrounds were 100% correlated mono. With practically all 5.1 soundtracks, I get plenty of sound out of the side speakers.

If you've tried EX decoding on non-EX soundtracks, does all the sound end up in your rear speakers?

Sanjay

I don't recall all of them...
But Pirates of the Carribean & Blade 3 have the Ex flag..

Many AVRs do not identify the incoming digital stream but the later HK AVRs such as the 745.. So many times the user has no idea what format the native stream, they see the Dolby Digital indicator but it culd be 2.0, 4.0, 5.1 or 6.1...

EX all the time??? Hmmm. I finally got the lats 1% of functionality programmed into my Harmony 880 Universal Remote yesterday.

So all my sound modes are now available on the activity screens, so I was going a ton of switching back and fourth.

It is your software, you own it, use it how you see fit.

I could detect difference, but not that one was really any better than any other most of the time.

I was comparing using the 5.1 NFL play off games. Where all the movie modes ruled, but all had great performance.

EX
DPLII - Movie
THX - Cinema
THX - EX Cinema
DPLII Movie + THX

ect..ect..ect...

I actually think at least one of the games must of been running the EX flag because the AVR seem to be auto selecting it.

Our questions related to the PLIIx flag - not the EX flag. I believe that there is no such thing.

Ed

I agree with the front 3 speakers that there is a noticeable difference between pro-logic center decoding and stereo phantom imaging, but it is not a dramatic one if your stereo pair are set-up properly.

However, I find it very difficult to distinguish between 5.1 and 6.1/7.1 (either EX or PLIIx) behind me. It may be, since I use omnipolar surrounds, that the sides image behind me better than direct radiators would.

Still, in listening to side/rear panning effects in an A/B between straight 5.1 and PLIIx, I can rarely if ever pinpoint a difference in favor of using the rears. In fact, I often notice with 5.1 soundtracks that the soundstage is pulled too far to the rear with PlIIx applied and, most of the time, I prefer to listen to 5.1 in 5.1 and save the rears for EX/ES soundtracks.

You are confusing the issue..
If the source material has the subject flag encoded..
Then the DSP will handle it appropriately, EX is for AVRs with 6.1 outputs and PL2x is for AVRs 7.1 outputs.
Ex is electrically equivalent to Dolby Digital 5.1 combined with PL2x movie mode
for 6.1 outputs.

Keep in mind...
Dolby strongly recommends 7.1 over 6.1 as back surround L/R speakers in a 7.1 system offers significantly greater spacial capability compared to 6.1 using a single back center speaker. Also in many AVRs the user can choose which DSP mode is activated by the subject flag either EX or PL2x Movie.

Sometimes with certain source materials when the AVR is set to the EX mode, the surround signals may appear too strongly from the center back rather delivering a wrap-around effect. In these cases Dolby recommends using PL2x Music mode as here the DSP will distribute the center back effects across all surround speakers.

I hope that clears up any misunderstanding you may have, post back if more questions...

Does anyone know for sure if PLIIx leaves the front 3 channels unchanged? I used to run everything using PLIIx until recently I started playing around with it again. It seems to me that the front channels do change slightly and I now prefer just standard 5.1. The most noticeable difference is in bass, but maybe that is just the bass management causing things to sound different with more speakers added in. Most of this was done listening to concert DVDs, but some movies as well. In my searching on the web I did read that the primary difference between PLIIx and DTS Neo 6 is that DTS leaves the fronts unmodified where as PLIIx tweaks them. Any truth to that? I don't have the equipment to monitor what comes out of the fronts in each scenerio but maybe someone here does.

PLIIx always processes only 2 channels, irrespective of the number of channels in the source material. When fed stereo content, the circuit sees 2 main channels and selects processing that will steer that information over 6 or 7 speakers. When fed 5.1 or 6.1 material, the circuit sees only 2 surround channels and selects processing that will steer that information over 3 or 4 speakers. Of course, those are two very different processes.
Not with multi-channel sources but possibly with 2-channel material. At one time the Neo:6 Music mode used to leave the front L/R channels untouched while still adding extracted centre and surround channels. The Movie mode cancelled the centre and surround info from the L/R channels. I'm not sure whether Neo:6 Music still works the same way (the processing has gone through at least 5 versions at this point).
How about a simple experiment? Unplug all your surround speakers and play some 5.1 material. Switch PLIIx on and off, and listen for a difference in your front speakers. Careful not to confuse changes in volume level with changes in content.

Sanjay

Good idea, I'll see if I can give that a try today. But if switching PLIIx on/off with 5.1 sources changes volume level in the fronts I'd consider that changing the source wouldn't you? Because if volume level does change it could mean sound is being smeared to the surrounds.

I ran that little test. First I need to clarify. I have a 6.1 receiver and can only apply EX or PLIIx Music to 5.1 sources. I guess I previously thought I was applying PLIIx to everything but I was only apply EX for 5.1 sources.

I didn't notice any change when turning on EX. Turning on PLIIx Music I may have noticed a very slight change but that could just be me switching back and forth and not hearing the exact same part over again. I guess I'm surprised. Based on how different straight 5.1, EX and PLIIX Music sound I can't believe it is simply the surround channels.

No. It's no different than adjusting the main volume knob to a comfortable level. Doesn't do anything to the source itself or the content of the front 3 channels.

The reason I brought up level change is because some receivers will slightly lower the volume of each speaker when you switch from 5 to 7. This keeps the overall volume level the same, even though you now have 2 more speakers making sound.
EX decoding can only be applied to 5.1-channel sources, but all PLIIx equipped receivers should be able to apply the processing to 2-channel material. Try it again with a CD.

Sanjay

I understand that. What I thought was interesting is with 2 channel sources I can do PLIIx Movie or PLIIx Music, but with 5.1 I can only do PLIIx Music (or EX of course).