ProLogic IIx degredation?

[Rolyasm]

Anyone know what happens to the sound quality when a receiver converts a 5.1 signal into a 6 or 7.1 ProLogic IIx? Does the sound quality suffer? Will my 5.1 sound the exact same, only now I have the rear surrounds as well? Only reason I ask is my friend has a 6.1 speaker configuration and he had his receiver set for PLIIx. When I changed it to Dolby Digital 5.1, I thought it sounded better. He thought it was a bit crisper also. Any thoughts? Also, I guess this applies to 2 channel and the other Pro Logic formats. If I played in Stereo and then switched to PL, would my main speakers suffer any degredation? I looked all over the Dolby site and didn't find any answer. thanks

Roly

[Aussie Geoff]

Rolyasm,

This is a complex question, and a good one...

When converting 5.1 to 6.1 or 7.1 Prologic IIx will change the sound of the rear two surrounds in order to create the extra 1 or 2 rear speakers. Essentially it will take away some of the common sounds from the left and right surrounds in order to add them to the rear speakers (how much is taken away depends on how much is common between the two surround channels. So with good quality rears and surrounds the sound is different but no worse in quality and much better specially positioned. A caveat to that is if the processor implementing the IIx algorithm has a limited resolution (e.g. 24 bit vs 32 bit vs 38 bit etc) then some of the resolution of the rear sound may be lost... This is quite subtle and only likely to be noticeable in cheaper or older IIx implementations. Personally I wouldn't be without it... If you are hearing a difference that you don't like, consider first factors such as the set-up of the speakers and the relative sound levels and distance (delay) settings for the surrounds and rears. These need to be accurate to get a good sound field.

However the story for processing 2 channel sound is much more complex. Here the sound is heavily manipulated by the II x algorithm in order to look at things such as the phase shift in the sound to dynamically position different types of sound around the room. This involved very high levels of active feedback (40db or more) and unquestionably changes the character of the sound. In terms of a good system and a pure stereo image many well sense a loss of the 3D stereo image... However the trade off for that is a 7.1 sound field that is enveloping in its own way. Again the quality of the final sound field depends a lot on the resolution of the processor doing the digital manipulation....

Geoff

[Rolyasm]

Geoff,
Thanks for the reply. Good to know all of my questions are completey stupid. I also have an email into Dolby to ask them. So it sounds like I won't lose any quality from the front mains or center, only the surrounds. That is good. I apprectiate the response and will let you know what Dolby tells me.
Roly

[Azeke]

Roly,

Below are two URLs which should enhance your knowledge further on Dolby Pro Logic IIx:

Dolby Pro Logic IIx Layout -Click on Dolby Pro Logic IIx

Dolby Pro IIx Library- Drop down box-Click on Dolby Pro Logic IIx

I actually have 7.1 utilizing DoPro IIx, simply stated, the center back channels are synthesized in stereo, instead of the previous mono track.

It is truly a beautiful thing, but you must have the pre-requisites, as Geoff previously stated, including enough room area.

Keep us posted on Dolby's feedback.

Hope this helps,

Azeke

[Shane Martin]

Roly,
My experience goes like this:

Some movies it sounds great with DPLIIX, Some don't.
As far as music goes, I didn't like the effect. Then again I don't care for multichannel music either. I think it's hokey.

[marshahu_cr]

Dolby Pro logic IIX for me provides a much wider soundfield and an enveloping experience for Dolby Digital Soundtracks - much more than DPLII where I struggled to hear the rear surround speakers. It also ensures that my surround back speakers dont go to waste! However I have noticed a slight degrading in the quality of the sound when its being decoded through the DPLIIX algorithm. This is even more blatant when the algorithm is applied to a DVD Audio.

I think it depends on which mode of DPL IIX you use. With movie and gaming mode, the degrading is very slight and hard to tell with all the effects being more pronounced, but with music mode I noticed that the sountrack had degraded and it sounded ever so slightly like there was a tube up against your ear creating a "hollow" sound. The Left, Right and Center speakers were a lot clearer in music mode and the bass was a tad stronger but I found that the rear surround speakers and surround backs had a slight "hollow" effect, the effects were poorly pronounced and the overall quality was severely compromised.

What is the point in receivers having all these futuristic Dolby Digital EX standards when only 5 movies or so use the damn format!?!?! Using these alogrithms destroys the entire soundtrack!!

[Rolyasm]

I agree. Lets get the movie guys up to speed and offer 7.1 with all movies.

[marshahu_cr]

The only movies that are out that are even touching the Dolby Digital EX format are Lord of the Rings and Star Wars Episode I, II and III and even they are only in 6.1!!! :roll: So when experiencing it on a 7.1 system the rear center is dispersed across the two surround back speakers! :cry:

Bring on GENUINE 7.1 sountracks, I'm fed up with either having silent surround back speakers or a degraded soundtrack as the result of using algorithms!! :P

[Rolyasm]

Just curious. Can you tell a difference with the true formats, ie. LOTR, Star Wars vs. the matrixed formats like DPLIIx? I am hoping my system will be ready in a month or so and then I can experiment also. Later
Roly

[Shane Martin]

The only movies that are out that are even touching the Dolby Digital EX format are Lord of the Rings and Star Wars Episode I, II and III and even they are only in 6.1!!!

There is a much larger list than that. And don't forget about DTS ES Discrete. HTF has a long list on a thread. I could probably think of 20 movies in my 300+ dvd collection that have a 6.1 soundtrack on it(natively).

[marshahu_cr]

The difference is noticeable but not as noticeable as switching from say, stereo or even Dolby Surround. The sound surrounds you more then traditional 5.1 systems and is useful for those dodgy rooms where you can never be in the centre of the soundfield, although its hardly a huge improvement over the traditional 5.1 format, especially for movies where the material is extracted from the existing DD 5.1 data - these are usually just effects shared with the Surround Left and Right channels or ambient effects as with Dolby Surround soundtracks.

In my instance my setup is shoehorned into an English Living room with the TV in the corner, and for the purposes of comfort the viewer usually sits at on end of the sofa. On a 5.1 system this meant that one of the surround speakers would be louder than the other and the ambient effects wouldn't be so enjoyable as it would be sitting in the center of the soundfield. However with the surround back speakers the experience is far more encompassing and I hardly notice the absence of the opposite surround channel since the surround back carries the effects from there closer to my ear!

Another random fact I noticed - very few DVD players, including the top of THX select players have 7.1 output or native support for Dolby Digital EX or DTS ES. I can still enjoy these formats on my DVD player but only because it relies on my decoder to decode these formats!!

[Shane Martin]

very few DVD players, including the top of THX select players have 7.1 output or native support for Dolby Digital EX or DTS ES. I can still enjoy these formats on my DVD player but only because it relies on my decoder to decode these formats!!

False. First there is no 7.1 output right now. DTS and DD EX are 6.1 and 5.1 formats. EX is derived from the 5.1 track to matrix a rear fill while DTS ES has a discrete version which is truly 6.1. Otherwise 7.1 is only a DSP mode ala Logic 7 or DPLIIX.

They natively support DTS ES and DD EX. They output it digitally to your pre/processor and it decodes it into the EX/ES signal. The problem is the flag on the DVD isn't necessarily active all the time. Nowadays it isn't much of a problem but it has been in the past.

[marshahu_cr]

False. First there is no 7.1 output right now.

Thats what I meant - even the top of the line DVD players don't have 7.1 analogue output. Maybe I misinterpreted what I meant - I meant that the DVD Players don't support DD EX and DTS ES using the Analogue output as you would with DVD Audio Discs - they rely on Digital output and the decoder takes care of the rest. The DVD players dont carry the Dolby Digital EX or DTS ES badge on the actual unit, therefore the amp must be what does all the work!!!