Film-Tech Forum ARCHIVE: How are the 7.1 mixes handled in 5.1 theatres?

This is topic How are the 7.1 mixes handled in 5.1 theatres? in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Lyle Romer (Member # 1266) on 10-21-2010, 09:02 AM:

With SDDS the processor would mix down the 8 channel mixes to 5.1. With digital cinema having discrete channels, what do they do with the 7.1 channel mixes? Is there a "dual inventory" where 5.1 channel mixes are provided to theatres not equipped for 7.1? Does the Digital Cinema Server have the capability to mix down (I didn't think it did).

Posted by Mark Strube (Member # 4190) on 10-21-2010, 12:08 PM:

Both versions are provided on the drive. Both the 5.1 and the 7.1 files must be loaded for the 7.1 auditorium, as the 7.1 file contains only audio to augment the existing 5.1 file, which is the one including the video.

I'm not sure what kind of downmix might happen if you'd run a 7.1 version in an auditorium not set up for that... but my best guess is you'd just be missing part of the surround track. So: no downmix in most cases, unless something is specially set up for this... which would be pointless as long as 5.1 versions are still readily available- which is the format that the vast, vast majority of digital films are still in. (Hasn't Toy Story 3 been the only 7.1 release so far?)

Posted by Lyle Romer (Member # 1266) on 10-22-2010, 08:04 AM:

Doe that mean that the 5.1 mixes are just missing all the back surround audio or does the 7.1 audio file overwrite the surround data for the Left and Right side surround channels?

Posted by Mark Strube (Member # 4190) on 10-22-2010, 02:25 PM:

If you play the 5.1 version of the file, that's a seperate mix intended for 5.1 auditoriums... so you wouldn't be missing sound. If you play the 7.1 version of the file in a 5.1 auditorium, then you're missing sound. (Assuming it would work at all, I haven't tested it myself.)

Posted by Marco Giustini (Member # 4544) on 10-24-2010, 10:52 AM:

No processors are able to mixdown audio. If you play 7.1 in a 5.1 theatre using 5.1 PCM you will lose back surrounds. If you play 5.1 using 7.1 format, your back surround won't play any sound.

This is an issue IMHO because there is no automation at the moment. And I do believe that the average cinema won't bother to switch the processors between 5.1 and 7.1.

Posted by Pete Naples (Member # 761) on 11-08-2010, 01:25 PM:

Marco, this is not strictly correct.

With CP650 one can assign 5.1 and 7.1 to different buttons, and select them when appropriate on the timeline, at least if using a Dolby Server.

Same goes for CP750/Dolby Server.

We've quite a few sites where the ads & trailers are run in 5.1, and 7.1 selected for the feature if it's a 7.1 mix.

Posted by Marco Giustini (Member # 4544) on 11-09-2010, 10:59 AM:

Hi Pete

That is correct.

What I mean is that you have to select the format on the playlist, there is no automation inside the processor or from the server itself that can recognise whether the sound played back is 5.1 or 7.1. If you do not change the sound format to 7.1 at the beginning of the 7.1 trailer/feature, and put it back to 5.1 at the end, you'll have missing channels in the auditorium. I can't think of many sites where there are projectionists skilled enough to understand and setup this kind of (very basic, I agree) setup.

I am expecting 7.1 auditoriums running everything in 7.1 sound all the time.

Posted by Pete Naples (Member # 761) on 11-09-2010, 02:57 PM:

I see what you're saying, unlike say SR.D EX there's no metadata to tell the CPxxx what it's supposed to be doing. A bit like servers not being able to self switch between 2D/3D/Dolby 3D.

I have to take you to task on "I can't think of many sites where there are projectionists skilled enough to understand and setup this kind of (very basic, I agree) setup." I can! All the sites I have setup thus far for 7.1 have this licked.

Posted by Marco Giustini (Member # 4544) on 11-09-2010, 04:01 PM:

Hi Pete

Yes, but the difference is that you can run 2D content with 3D macro; you can't run 7.1 with 5.1 or vice-versa.

Sure, hopefully there are sites with someone able to perform such a basic skills, but in my limited experience it's much more likely the contrary, don't you agree?

EX is a good example: I can't think of any sites that have ever setup the EX properly. Before the 'auto-ex' feature I saw a number of sites with the CP650 contantly on Format 13, or with the SA-10 constantly activated. I remember a projectionist that was sure the SA10 activates itself only when the back surround was used.

I may be mistaken, but I see this 5.1/7.1 matter as a possible issue.

Posted by Pete Naples (Member # 761) on 11-09-2010, 04:58 PM:

Perhaps I am spoiled, but on the whole I have to disagree.

Most of the sites I service would get this right, once they've been trained on the how and more importantly, the why.

Perhaps up here in the frozen North we haven't lost sight of the importance of good presentation [Wink]

Posted by Marco Giustini (Member # 4544) on 11-09-2010, 05:17 PM:

Keep in mind that my direct experience comes from Italy, I don't know how 'right' film is done over the UK. But I wasn't very impressed by most of the show I attended. Actually, I stopped going to the cinema. But let's not go OT.

I do believe that an automatic feature that triggers 5.1 and 7.1 formats (and 7.1/5.1 decode mode on 750) would be advisable.

Posted by Frank Angel (Member # 248) on 11-09-2010, 08:01 PM:

If a system were left in 7.1 format, how would that effect a film mixed only for 5.1? Marco says "If you play 5.1 using 7.1 format, your back surround won't play any sound." But if you played a 5.1 film correctly in the 5.1 format, you wouldn't get any sound out of the rear anyway, would you? So that wouldn't seem to be a bad solution -- to just play everything in 7.1. Unless the 5.1 format assigns sides to be duplicated into the extra surround channels that become discrete in 7.1

Posted by Lyle Romer (Member # 1266) on 11-09-2010, 08:04 PM:

At least with EX, a standard 5.1 mix will use the left rear speakers along with the left side to make the "left surround" and the same for the right.

I assume the intent is the same with digital cinema.

Posted by Marco Giustini (Member # 4544) on 11-10-2010, 04:26 AM:

Hi Frank

No, there is a huge difference!

Back surrounds are discrete in D-Cinema, they are not extracted like EX. If you playback a 5.1 using a 5.1 format, the processor will copy the Left surround into the BackLeft Surround, and the Right Surround into the BackRight Surround (exactly what happens when you're playing back a 5.1 in a EX theatre). If you playback a 5.1 using a 7.1 format, Back Surrounds are playing back different Digital Inputs, but since you are playing back a 5.1 source, those inputs will be silent.

The difference would mainly be in surrounds' level, it will be too low if you playback a 5.1 using a 7.1 since the surround level is made taking into account that ALL surrounds are working.

Does it make sense?

Posted by Dave Macaulay (Member # 813) on 11-17-2010, 10:38 PM:

How do you assign both 5.1 and 7.1 in a cp750? There's only one 4xAES input, and only one button (or external command) to select it. 7.1 can only be selected from the front panel as far as I can find - there's no serial or tcp/ip string for it.

Posted by Steve Guttag (Member # 268) on 11-18-2010, 01:29 AM:

There is indeed a serial string for it...something like "discrete surrounds". Do a poll on the available strings on an upgraded CP750 and it will tell you what it is.

Steve