Pre/pros that can generate 6.1 from 5.1 (1 Viewer)

[Dzung Pham]

Besides the Outlaw 950 (with its Cirrus Extra Surround), and the Rotel RSP-1066 (with its eXtended Surround), are there any other pre/pros out there that are capable of deriving 6.1 channels from all the major 5.1 formats (DTS5.1 (non ES), DD5.1 (non EX), or DPL2) ? I know Lexicon has Logic 7 but it does not seem possible to use L7 with a 6.1 speaker setup. This seems to be a very useful feature but I don't see any indication that it is available on many other pre/pros, such as the Anthem AVM20 or the Integra RDC-7.

 

[Harold_C]

There is considerable confusion in the marketplace about extended surround functions. With the exception of DTS-ES Discrete, the center back channel signal is derived from the two surround channels of a 5.1 channel disc by a matrix decoder similar to the center channel function of Dolby Pro Logic. Some 5.1 channel discs are recorded with a center back channel signal specifically encoded in the mix; however, that is not necessary for a matrix decoder to derive a center back signal based on amplitude and phase relationships in two surround channels.

Matrix decoders are well understood and widely implemented, whether or not they carry a tradename such as "Dolby Pro Logic", "Dolby Pro Logic II", or "DTS Neo:6" for multi-channel surround from stereo sources or "Dolby Surround EX", "DTS-ES", or "Rotel XS" for 6 and 7 channel surround. I think you will find that most 6.1 channel pre/pros or receivers that provide center back channel outputs also have some kind of digitally implemented matrix decoder for deriving center back signals from the surround channels on any kind of 5.1 channel recording.

The reason that these decoders are not all labeled "Dolby Surround EX" is that Dolby signed an exclusive deal with THX to offer "Surround EX" for a period of time. So, up to now, the only units with a "Surround EX" label were those units that paid for a THX license. Didn't matter. Everybody else just used their own decoder and didn't call it Surround EX.

In fact, since Dolby has failed to embed a Surround EX "flag" in their Surround EX discs, most Surround EX processors have no way of recognizing a Surround EX disc and activating the "official" decoder mode. Most of them are using their proprietary decoder modes to extract a center back channel from these discs, just as if they were regular 5.1 channel discs.

It appears that the same decoder is generally used, even if Surround EX is activated (by the "flag" or manually): the decoders just have two modes: one for matrix encoded 5.1 discs and one for non-matrix encoded 5.1 discs. The two modes differ slightly in how they set the levels of the derived surround channels relative to each other (just like different settings of the "Center Width" feature in Pro Logic II decoders change the relative levels of the front three channels). In effect, processors have had a "Surround EX" decoder for the last year or so -- they just couldn't call it that because of Dolby's exclusive deal with THX. Now, they can call it that if they pay the additional license fee to Dolby for the "Surround EX" logo and light in the display.

Implementations like Rotel XS are very handy. If you've got a center back channel or channels configured in your speaker setup menu, the XS decoder will automatically extract a center back channel signal from any source that has a stereo surround mix -- 5.1 discs, Surround EX discs, even Pro Logic II decoded stereo recordings. You don't have to do anything or worry about it at all.

 

[Dzung Pham]

Harold, I'm not sure I understand what you're saying. Are you saying that all EX decoding pre/pros are capable of doing a good job of providing a rear center signal? It is my impression that if you apply EX decoding to a non EX encoded signal, the sound will collapse into the rear center. For example, the Anthem AVM20 manual states the following:

If Surround EX is applied to 5.1-channel material that is not encoded in Surround EX, mono information in the surround channels is routed to the rear channels through Pro Logic matrix decoding on the surround channels only.

My understanding is that the Outlaw CES and Rotel XS modes do a better job distributing mono information to all surround speakers (increasing the "center width"). This does not seem to be a standard feature on most pre/pros however, even though it does not seem like it would be that hard to implement.

 

[Harold_C]

I'm saying that Rotel XS and similar decoder algorithms probably do at least as good, if not a better, job than the Surround EX specific decoder modes with ALL discs -- standard 5.1 and Surround EX 5.1 recordings.

I'm also saying that unless your pre-pro has a button somewhere to manually force it into Surround EX mode (as opposed to the always active Rotel XS mode, for example), you will be decoding Dolby Surround EX discs with Rotel XS -- until Dolby gets around to actually releasing discs with the proper Surround EX "flag".

The difference between the two modes is essentially the same as the difference between "wide" and "narrow" center width on Dolby Pro Logic II.

 

[Dzung Pham]

Thanks for the clarification, Harold, that's what I thought. But based on the lack of responses so far, I guess I am correct in that the Rotel and the Outlaw seem to be the only pre/pros that have this feature available. I wonder if the Anthem's upgrade will include it.

 

[Kevin C Brown]

Dzung- I know for certain that the B&K Ref 30 *doesn't* have modes like that. (I know because I almost bought one.)

I *suspect* that any pre/pro more than let's say 6 months old, probably *doesn't* have modes to "expand" 5.1 sources to 6.1/7.1.

A lot of receivers have those modes today, but not pre/pros.

(Excepting of course Logic 7.)