# whats the best sound mode to use on 7.1 setup



## jwhiteman (Mar 14, 2013)

I've been running 5.1 for so long and never took advantage of the 2 extra channels, finally hooked up the 2 extra channels, but what's best mode to use all channels for movies? I have a Onkyo 906


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## tonyvdb (Sep 5, 2007)

I use the THX Ultra as it takes any of the 5.1 mixes and expands it to the 7.1 channels. It sounds fantastic on my setup. we have almost identical receivers other than you have the better video upconversion.


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## jwhiteman (Mar 14, 2013)

Are you referring to ultra 2 cinema mode?


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## htsirhc (Jul 21, 2012)

I just upgraded to denon 3313ci from avr890 and moved my s.backs to front heights. So far I'm impressed. I've only tried DTS PLiiz so far. I will continue to run through some other modes this weekend. But as of now I'm liking my fronts. My room is more accommodating for heights rather than s.backs as well.


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## sdurani (Oct 28, 2010)

Dolby Pro Logic IIx. Whether you're listening to 2-channel material or 5.1 material, PLIIx does a great job of scaling the number of _channels_ in the source to the number of _speakers_ in your layout. 

For 5.1 sources, PLIIx will extract stereo surround-back channels, so that you not only have side vs rear separation in the surround field, but also left-vs-right separation behind you (easier to hear if your rear speakers are spread wide apart).


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## tonyvdb (Sep 5, 2007)

jwhiteman said:


> Are you referring to ultra 2 cinema mode?


Yes, it does a much better job than DPLIIx


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## sdurani (Oct 28, 2010)

tonyvdb said:


> Yes, it does a much better job than DPLIIx


Only if you believe mono is "much better" than stereo when it comes to surround-back extraction.


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## jwhiteman (Mar 14, 2013)

What do you recommend then?


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## tonyvdb (Sep 5, 2007)

Where do you get that the rears are only Mono with THX processing?


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## jwhiteman (Mar 14, 2013)

tonyvdb said:


> Where do you get that the rears are only Mono with THX processing?


Im confused about that to makes no sense.. hes suggesting theres a better mode but doesnt mention what it is lol


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## tonyvdb (Sep 5, 2007)

jwhiteman said:


> Im confused about that to makes no sense.. hes suggesting theres a better mode but doesnt mention what it is lol


I think he is talking about using DPLIIx


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## sdurani (Oct 28, 2010)

tonyvdb said:


> Where do you get that the rears are only Mono with THX processing?


When THX Ultra2 was first certified in pre-pros and receivers, Sound & Vision (or whatever it was called back then) did a review on it. THX reps came by to set up the speakers (introducing their new recommendation for the rear speakers to be placed next to each other) and explain how the new technologies in the Ultra2 spec (Adaptive Speaker Array, Boundry Gain Compensation, and their new post-processing modes) worked. 

Turned out that THX Music mode simply copied the side speakers to the rear speakers, in order to use phantom imaging to create a pair of virtual speakers between those locations. THX Cinema mode extracted a mono surround-back channel, like their previous THX Surround EX decoding mode. Not unusual, since other processing modes at the time, like DTS Neo:6 and SRS Circle Surround II, likewise extracted a mono surround-back channel from 5.1 sources. The difference was that THX decorrelated the rears (make them out of phase with each other) in order to prevent surround-back info from localizing at the centre of the back wall. 

To further minimize hot-spotting at the middle of the back wall, both THX modes (Music and Cinema) use ASA, which is a Spatializer-like processing that makes a pair of speakers sound further apart than they physically are (you probably have something similar on one of the TVs in your home, which attempts to do kinda-sorta surround sound from 2 speakers). This is the only reason you have to tell your THX certified receiver how far apart your rear speakers are during initial set-up (the wider apart, the less ASA processing it applies). 

One thing they never explained in the article is why place your rear speakers next to each other, only to then use processing to make them sound like they're further apart. Thankfully it looks like they're going back recommending their pre-Ultra2 speaker layout, with the rear speakers spread 60 degrees apart (at least according to the latest diagrams on their website). Newer 7.1 soundtracks have stereo surround-back channels, like PLIIx does, so it makes sense to spread the rear speakers apart in order to hear left-vs-right separation (can't hear that with the speakers next to each other).


jwhiteman said:


> Im confused about that to makes no sense.. hes suggesting theres a better mode but doesnt mention what it is lol


lol read my previous post in this thread and you wont be confused lol


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## tonyvdb (Sep 5, 2007)

This may not be the case anymore as in my receiver anyhow it has the option that you select greater than 4ft apart for the actual spacing of the two rear channels. Im positive its a stereo signal


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## jwhiteman (Mar 14, 2013)

sdurani said:


> When THX Ultra2 was first certified in pre-pros and receivers, Sound & Vision (or whatever it was called back then) did a review on it. THX reps came by to set up the speakers (introducing their new recommendation for the rear speakers to be placed next to each other) and explain how the new technologies in the Ultra2 spec (Adaptive Speaker Array, Boundry Gain Compensation, and their new post-processing modes) worked.
> 
> Turned out that THX Music mode simply copied the side speakers to the rear speakers, in order to use phantom imaging to create a pair of virtual speakers between those locations. THX Cinema mode extracted a mono surround-back channel, like their previous THX Surround EX decoding mode. Not unusual, since other processing modes at the time, like DTS Neo:6 and SRS Circle Surround II, likewise extracted a mono surround-back channel from 5.1 sources. The difference was that THX decorrelated the rears (make them out of phase with each other) in order to prevent surround-back info from localizing at the centre of the back wall.
> 
> ...


So what are you saying is best mode then? Lol


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## asere (Dec 7, 2011)

tonyvdb said:


> This may not be the case anymore as in my receiver anyhow it has the option that you select greater than 4ft apart for the actual spacing of the two rear channels. Im positive its a stereo signal


I know this tread is old but I ran across what you said since lately I have been reading more about THX. I have the 805 like you and I did run across the 4ft apart spacing option for the rears. 
Is 4ft the way to go?


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## willis7469 (Jan 31, 2014)

Huh, funny meeting you in here. Lol
Can't speak for Tony, but mine are greater than 4' so that's what I chose. Works great.


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## asere (Dec 7, 2011)

willis7469 said:


> Huh, funny meeting you in here. Lol
> Can't speak for Tony, but mine are greater than 4' so that's what I chose. Works great.


 Yeah that sounds about right. Thanks


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