What happens to 5.1 signal in a 6.1 system? (1 Viewer)

[Ryan Tsang]

If the receiver/processor is selected to one of the 6.1 formats, is there output from the rear center(s) when playing a 5.1 soundtrack?

or will the receiver/processor not allow you to select 6.1 when it detects a 5.1 signal?

Thanks!

 

[Michael Reuben]

There is currently only one "6.1" format, known as DTS-ES Discrete, and it only exists on 23 titles. All other so-called "6.1" titles are merely 5.1 titles from which a decoder synthesizes an additional channel from the left and right rears. Most decoders will happily apply the same processing to a title regardless of whether the track has been specifically encoded for it. Results vary, depending on the mix and individual taste.

M.

 

[Steve Schaffer]

Michael is technically correct.
DTS ES Discrete is the only format with a discretely encoded rear center channel. DD-ES and DTS-ES Matrix formats are specifically coded to derive a rear center channel from the two regular surround channels, similar to the way regular Pro-Logic coding got a front center and surround information from a 2 channel source. It's not discrete but works fairly well.

Also as Michael stated, most all DD-EX/DTS-ES decoders will synthesize a rear center from 5.1 material that lacks the specific ES or EX matrix rear center coding, just as pro logic decoders would attempt surround decoding of non-pro logic encoded 2 channel sources.

How well this works is probably going to vary by source material and/or the particular processor in the pre-pro or reciever.

I have a Pioneer VSX-45TX and use EX/ES mode for all the regular 5.1 movies I've played, with very nice results. Many of the movies with non-EX/ES coding still playback with a very convincing rear center effect, and I've yet to find one that sounds better with the EX/ES matrix decoding turned off. I've even used it with DPLII processing of 2 channel sources (Tomb Raider from Directv) and gotten nice results.

 

[Ryan Tsang]

Thanks guys! I plan to upgrade my Acurus ACT-3 to 6.1 and by the sounds of it (no pun intended), I'll leave 6.1 decoding on at all times.

 

[JamesKr]

Don't forget about 7.1!

I have two rear channels which replace a rear center. The rear channnel speakers are about 5 feet apart. To the best of my knowledge, 7.1 plays the same sounds from both rear channels as if they were both rear centers. The 7.1 format gives a more immersive rear sound than 6.1 does due to the dual channels.

 

[Ryan Tsang]

jameskr: You're absolutely right. I too, would use two rear center when the time comes.


There seems to be an inconsistent use of terms, and it can be misleading when "7.1" is made to sound like a format.
I'm not counting Logic 7.

6.1 describes the number of channels used (discrete in DTS-ES, matrixed in THX-EX and DTS-ES matrix)

7.1 describes a system using two rear center speakers, and is based on number of speakers used.

Yet, Dolby advocates the use of two rear centers, to eliminate possibility of the "reversal" phenomenon. So in practice, an ideal setup for 6.1 playback is 7 speakers + sub(s). So why the 7.1 designation at all? Just call it 6.1 and let the users decide how many center rears to use in their setup. We don't call our systems "5.2" if we run two subs do we?

 

[Scott Merryfield]

I have a Pioneer VSX-45TX and use EX/ES mode for all the regular 5.1 movies I've played, with very nice results. Many of the movies with non-EX/ES coding still playback with a very convincing rear center effect, and I've yet to find one that sounds better with the EX/ES matrix decoding turned off.

My experience is very similar to Steve's with my Pioneer VSX-47TX. I use the EX/ES processing for all 5.1 material (except SACD and DVD-Audio) and have yet to find a film where the surrounds completely collapse to the rear center speakers.

 

[Michael Reuben]

So why the 7.1 designation at all?

Because it's a better sales pitch. People fixate on the number of channels and feel they're missing out if they don't have absolutely the maximum number.

M.

 

[AaronBatiuk]

If the receiver/processor is selected to one of the 6.1 formats, is there output from the rear center(s) when playing a 5.1 soundtrack?

On some receivers, yes, but only sometimes, on others, no, not at all.

Consider the speaker placement in a theatre:

 L L C C R R
 
 SL SR
 
 SL SR
 
 SL SR
 
 SBL SBL SBR SBR

Where L=left C=centre R=right SL=surround-left SR=surround-right SBL=surround-back-left SBR=surround-back-right. These are just names I gave them so I could refer to the different speakers easily. There will also be a number of subs, but I left them out. There are also likely more speakers than I drew, but you get the idea.

With old Dolby Surround soundtracks, there was only one 'surround' channel; all off the speakers along the side and rear walls played it.

With a 5.1 (Dolby or dts) surround soundtracks, the SL and SR speakers play the left and right surround channels respectively. Note that the speakers along the back wall are also active: the SBL speakers play the SL sound, and the SBR speakers play the SR sound. So it is essentially:

 L L C C R R
 
 SL SR
 
 SL SR
 
 SL SR
 
 SL SL SR SR

If the thratre is playing an extended surround soundtrack (DD-EX, dts-ES), then the SBL and SBR speakers all play the SB (surround-back) channel sound. So it is like this:

 L L C C R R
 
 SL SR
 
 SL SR
 
 SL SR
 
 SB SB SB SB

In most 5.1 home theatres, we have only two surround speakers, at the sides, and have no surround speakers behind us. Since the seating area is comparatively small, and we usually sit in or near the 'sweet spot' this is perfectly OK (and certainly less expensive than lining the walls with speakers to get a diffuse sound!).
Now, however, we have 7.1 speaker systems, with two surround-back speakers in addition to the surround speakers at the sides. Some receivers (like the Sony STR-4ES that I own) use the surround-back speakers just like they are used in a movie theatre when playing a 5.1 (not extended-surround) soundtrack: they duplicate the left and right surround channels respectively. Note that you need two surround back speakers for this to work, and that this is not at all the same as forcing 6.1 decoding on a 5.1 soundtrack. This type of arrangement can be very effective in a home theatre, espeicially if you have more than one row of seating like a real theatre has, rather than one row of seating in the sweet spot. My HT has two rows of seating; having all speakers active for 5.1 sountracks creates a much better surround experience for the people in the back row.