Hi All,
So as I had posted in the 990 forum, I have finally added pair of back surround speakers to my h/t setup. After a couple of days messin' around with the new setup, I can say that it was a very worth while addition. So now that I've added the extra channels, I have a few questions and comments about surround formats that have become available in my Model 990.

I can now select Dobly Digital EX, even on sources that are encoded only as DD5.1. How can that be? Does the 990 just create the back surround channels out of the two descrete surround channels? If so, is this faux channel "matrixed" or descrete? Seems to be kind of faking it to me. If a sound source were encoded in DD EX, I could see the processor spreading that mono back surround signal across the two back surround speakers. But there's not even a matrixed channel there to begin with... I don't get it. That being said, why would I choose that option when I have Dolby PLIIx available to me? Dolby PLIIx supposedly creates two descrete back surround channels out of the surround channels right?

Another thing that I found strange was that I can add Dolby PLIIx to any DTS encoded source. Crazy. I can't imagine that the DTS folks are very fond of that. Seems to sound great though. I watched a couple of my favorite "Band of Brothers" scenes in DTS + PLIIx Movie and loved it. Yikes! Bullets zingin' over my head!

My last comment is regarding PLIIx Music. I rarely, if ever, listend to music in anything other than Bypass mode using the analog outputs of my Denon 2900 DVD player. I decided to try using PLIIx (still using the analog inputs) and really enjoyed what I heard. I spread the center channel evenly across the two fronts and turned on Panorama, but left it at that. As I mentioned, I liked what I heard. (Sorry 2-channel purists...)

So, those are my questions/comments. I am wondering what modes you all watch movies in. As always, thanks for listening to my rambling.


later,
simp

Hi Simp, Because EX soundtracks are 5.1 discrete channels, just like DD 5.1 soundtracks. The processing doesn't know the difference. The EX circuit extracts correlated (in-phase) mono information from the L/R surround channels and sends it to the two rear speakers. This surround-back information is also actively cancelled from L/R surround channels, so that it's not heard from the wrong direction. The leftover stereo surround information is sent to the two side speakers. That's how you get different sounds at your left, your right and behind you.

After EX decoding, none of the resulting three surround channels (left, right, back) have the same content as the original two surround channels on the DVD. Therefore none of them can be considered discrete anymore; all three are matrix derived.

However, keep in mind that 100% the information you hear from the surround speakers came from the original surround channels. None of it was "created" by the EX circuit, let alone the 990. When you sit in the sweet spot between two speakers, mono sounds will phantom image in the middle of the soundstage. Similarly, when you sit exactly between a pair of surround speakers, mono information tends to phantom image behind you. However, if you move out of this narrow sweet spot, this phantom rear image collapses to the nearest surround speaker.

As described above, the EX circuit removes this information from the side speakers and puts it into the rear speakers. Now, no matter where you sit in the room, those sounds will always image behind you (as intended). No magic involved, just a pair of speakers physically located behind you (makes it difficult for those sounds to come from any other direction).

This the same directionality as before, but now enjoyed by off-axis listeners as well. You can call that "faking it", but I prefer to call it what it really is: stable imaging.

Honestly, I can't imagine why you wouldn't use EX decoding on all 5.1 sources. Unless you had something better; which brings us to... You wouldn't. That's why Dolby themselves recommend using PLIIx processing instead of EX decoding, even on EX-encoded soundtracks. With PLIIx processing, the two surround-back channels are indeed stereo, but they're not discrete. As with EX decoding, it's only certain portions of the surround channels that are sent to the speakers behind you. The remainder of the surround information (with the surround-back information cancelled) is sent to the speakers at your sides.

If you were to look at any one of these resulting surround channels, none of them would exactly resemble the original surround channels on the DVD. So again, none of them can be considered discrete. Two discrete surround channels are input, four matrix-derived surround channels are output.

Just as EX decoding maintained the intended directionality of the original surround channels, PLIIx processing also takes its steering cues from the source material.

Sounds that would have phantom imaged over your left shoulder are steered to the left rear speaker. Sounds that would have phantom imaged over your right shoulder are steered to the right rear speaker. Sounds that would have phantom imaged directly behind you are sent to both rear speakers.

The only difference is that listeners are no longer limited to a sweet spot, since directionality in the surround field no longer depends on something as unstable as phantom imaging. With four surrounds spread out in the rear hemisphere, if a dinosaur roar is supposed to be heard from the left rear corner of the room, everyone will hear it from that direction. Not so strange. Dolby designed PLIIx to be format agnostic. Depending on how it's implemented on a particular pre-pro, PLIIx can be applied to: DD, DTS, DVD-A, SACD, PCM, even analogue. No apologies needed. It's been something like 14 years since I've listened to 2-channel music using only two speakers. PLIIx actually works quite well with all sorts of music. Try the first couple of minutes from the title track of Michael Jackson's 'Thriller' album.

As with the surround channels of 5.1 soundtracks, PLIIx actually does a decent job of respecting the original directionality. The only information sent to the centre speaker is correlated mono info, which would have naturally imaged there anyway. Uncorrelated (out-of-phase) information doesn't really image in the front soundstage; it kinda sounds more like it's coming from all over. And this is the specific information that is extracted and sent to the surround speakers.

The controls of PLIIx Music mode let you adjust the sound to your personal tastes. They're very useful, like when switching from acoustic jazz to studio pop to classical. You can dial it in to sound as subtle or as exciting as your mood (and the music) dictates. Don't believe that stuff about surround processing suddenly making a trumpet blare from behind you. PLIIx is a lot more ambient and tasteful than that.

I started this response almost two hours ago, but am just now ready to post it... Yeesh...

Dolby EX and DTS ES have always supported standard 5.1 tracks in the respective formats in addition to EX or ES-encoded tracks - EX really had to, since many early EX-flagged tracks were not identified as such (via flags or even labels on the packaging) due to concerns about confusing the consumer. Both EX and ES pre-date PLIIx, and can work well with 6.1 or 7.1 speaker setups. PLIIx, on the other hand, is a newer alternative that is solely intended as a support for other formats (stereo as well as converting 5.1 to 7.1). As part of that, Pro Logic IIx can be applied downstream of any processing mode, as long as that processing mode outputs 5.1 or less channels in the digital domain (which would cover PCM stereo from CD's or cable/satellite, Dolby 2.0 through 5.1 from DVD or cable/satellite, and DTS from DVD). Just to round out the weird world of PLIIx, it was introduced initially as an extension of PLII (carrying PLII from 5.1 to 7.1), but it can also act as an expanded replacement for PLII (so if you don't have a 6.1 or 7.1 speaker setup, you can still use PLIIx to extend from stereo to however many speakers you have available).

Wow!
Thanks for the most excellent responses guys. So, all the very informative, tecnical info aside, the ES and EX modes have been there the whole time, just didn't see 'em until I turned up the speakers in the back. I had no idea. Moreover, I always assumed that the source material needed to be encoded that way to get it, regardless of speaker configuration. Kind makes me wish that I'd added the two rear speakers while I still had my 950 so I could have tinkered with Cirrus Extra Surround mode. It'd have to have been pretty darn good to compete with PLIIx.

One more question and please forgive me if I missed something in Sanjay and Gonk's responses: What does a DVD that says that it's encoded in DD EX give me that one that's only DD 5.1 doesn't? Sounds like I could select DD EX as long as I have at least a 6.1 setup even if the DVD is only marked DD 5.1.

Again, thanks for all the help guys.


later,
simp

You can always select DD EX (although, as Sanjay points out, PLIIx is probably the preferred tool for the job), but a Dolby EX encoded title is similar to a Pro Logic encoded stereo track back in the days of VHS - the surround channels of a Dolby EX track are mixed so as to facilitate the extraction of a surround back channel. My way of thinking about it is that an EX track is one that gives the EX processing instructions on how to generate the sixth channel instead of asking EX to figure out it on its own.

Thanks, Gonk. That clears things up quite a bit. I guess I never put much thought into it, but there's actaully quite a bit going on inside of the Model 990. Pretty cool stuff. Thanks again for the responses.


later,
simp