Film-Tech Forum ARCHIVE: Mono Surround Sound?

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Posted by Paul Turner (Member # 832) on 04-17-2001, 02:37 PM:

I did a Film Tech search and found nothing, so maybe I didn’t see it here. Somewhere there was a discussion about mono surround sound systems. I’m running mono now and am looking into twinning the theater soon, so I don’t wanna invest in a digital surround system just to have to reinstall it later. However, my auditorium sound could use some help to conquer bad acoustics, so I was considering putting in surround sound system with the mono (if that's possible). Was wondering if anyone could comment on:

-what equipment would be necessary to go mono surround from a mono behind-the-screen system?

-is there a system that can be used when I go digital?

I know that a delay of about 1 ms per foot is needed on the surround speakers, so I’m hoping there’s a simple way to do it. While I’m at it, I’m hoping there’s a million bucks in my account . . . . Any input would be appreciated.

Posted by William T. Parr (Member # 677) on 04-17-2001, 02:52 PM:

Paul There are several options at your disposal here. For Mono Surround systems that will accomadate Digital later on you could go with Dolby CP65 and remove the L and R Cat 64 cards

. Dolby CP45 though I am not sure if it has Cat 64 cards or if everything in it is all Digital. Ultra Stereo you can get the DSP 60 everything on it is done in the Digital domain,

or a JS 223 or 230 model comes with only the cards to do Center and Surrounds (230) or Center split Surrounds (223).

Then there are several Smart Stereo Products available as well. Including the Mod IIIb and Mod IIc models which come in various configurations to suit your needs and are a good inexpensive alternative to the Familiar Names on the Market. All affirmetioned products support Optical and Digital Bass channels. Even you want something that will do Mono Surround and is a guiniune POS you could go with a Kintek KT2010

or an EPRAD Starscope, or maybe this version was called a Starlette? both are no longer made anymore and do not easily accomodate, if at all, Digital Sound. Kintek is no longer in business and support on their unit is next to nothing. Eprad is still in business, however the Starscope/Starlette units have not been made in 10+ years so support on them may be nothing also.

Posted by Adam Martin (Member # 641) on 04-17-2001, 04:04 PM:

I've always known it as center surround. Try a search for that. It's here somewhere.

Posted by Paul G. Thompson (Member # 655) on 04-17-2001, 06:49 PM:

Center-surround is a cheap shot. It is best to do it right.

Posted by Gordon McLeod (Member # 33) on 04-17-2001, 07:53 PM:

The CP65 can't easilly do centre surround because if you remove the L and R cat 64's you will just lloose that content. In a centre surround system a sum is sent to the centre speaker with no gain riding logic involved
The CP45 can be configured with a few component changes to do proper centre surround operation with the bonus of logic keeping the L and R out of the surrounds

The Mod6 from Smart will also do this as well and is the most economical unit on the market
All the other cneter surround units just send a differential signal to the surrounds so they can get very annoying

Posted by Steve Guttag (Member # 268) on 04-17-2001, 10:28 PM:

Gord:

The CP-65 can easily do Center-Surround or as it is more aptly named here...mono-surround. A pair of jumper wires are placed on the Cat. 242 to sum L, C and R to a common output. You can also make the CP-65 do a L, R and Surround (handy for small rear screen projection).

Steve

------------------
"Old projectionists never die, they just changeover!"

Posted by Jesse Skeen (Member # 586) on 04-18-2001, 04:37 AM:

More aptly named: RIP-OFF STEREO!

Posted by Danny Hart (Member # 659) on 04-18-2001, 07:07 PM:

I would just like to know why John Pytlak hasn't already been here with a link to some Kodak website page.

Posted by Gordon McLeod (Member # 33) on 04-18-2001, 07:51 PM:

Steve I don't advise that route since it is post matrix and as such there is som rather bizare artifacts of the gain riding circuitry that can be heard

Posted by Steve Guttag (Member # 268) on 04-18-2001, 09:37 PM:

Gord,

Please explain the "gain riding artifacts".

Personally, I never recommend mono-surround. Or 3-channel mono (but that is yet another thread )

Steve

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"Old projectionists never die, they just changeover!"

Posted by Scott Norwood (Member # 30) on 04-18-2001, 09:56 PM:

In case anyone cares, I agree with the opinions that others have expressed here--mono/surround is a pretty silly idea. I'd much rather listen to a really good mono system than some sort of wannabe Dolby system (or even a real Dolby system that isn't properly aligned). A really top-quality mono system can sound very good, although it seems that such an installation is quite rare, since theatre owners like to put "surround" or "Dolby" (or, now, "digital") on the marquee, without caring too much about the actual sound quality in the auditorium.

Posted by Adam Martin (Member # 641) on 04-18-2001, 10:09 PM:

I concur, Scott. Could it be "mono done right?"

The first time I even heard of center-surround was at the opening of a _new_ theater in 97 or 98. It was the second stupidest thing I'd ever heard of. The first came 30 seconds later, when I saw the "portable digital" connectors on the same rack. Turned myself around and walked right back down the stairs.

Posted by John Pytlak (Member # 331) on 04-18-2001, 11:13 PM:

Danny, here is a link to Dolby technical information, including surround sound:
http://www.dolby.com/tech/#head2

Here's Perry Sun's Movie Sound Page:
http://www.moviesoundpage.com

And Marty Hart's American Widescreen Museum:
http://www.widescreenmuseum.com/sound/sound01.htm

Plus some information on the Kodak website:
http://www.kodak.com/country/US/en/motion/programs/student/handbook/recording1.shtml

(Ron Uhlig of Kodak first developed and demonstrated stereo variable area tracks using Dolby noise reduction, and was very instrumental in developing Cinema Digital Sound (CDS), the FIRST system to record digital sound on the print.)

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Joe Schmidt (Member # 822) on 04-19-2001, 12:15 PM:

Well, here's another old sneaky trick which can work quite well, but you cannot appreciate how well unless you've actually been involved in some way with the "doing."

This might get me Scolded again but I'll risk it. How many here have seen "How to Steal A Million?" This had a mono track.

If you switch in the surrounds every time the burglar alarm in the museum goes off, you'll have a marvelous effect, and very cheap too!
A routine everyday use of the surrounds will be to switch them in for main title and ending music.

This has been automated in the past and at one time Century produced a little system for doing it, but in all cases you have to cue the prints manually.

Besides having a button at each projector for surrounds on/off, one method is to add a scanning device to constantly read between the sprocket holes. The "ON" signal is two drops of india ink a certain number of sprocket holes apart, such as five, and "OFF" is just one drop. This helps to maintain OFF as the default so that an occasionally anomaly such as a bit of dirt or a splice won't accidentally trip the surrounds on when not wanted. The associated logic circuitry searches continuously for a correct ON signal, when read it closes a relay to switch on the surrounds, then watches for the OFF signal.

This can be a lot of fun. Of course you don't need it with current product today as surround activity is all built in with the sound recording, and so we wouldn't bother.

Posted by Paul Turner (Member # 832) on 04-19-2001, 03:10 PM:

Thanks for all the feedback, kids. I'm gonna hook up with my equipment supplier and see what he has. We'll see what happens!

Posted by Gordon McLeod (Member # 33) on 04-19-2001, 06:22 PM:

Steve the gain riding artifacts are frm the gain riding in the matrix
I you have a realy busy track there is a lot of pumping occurs if you sum them.
One would be better to actually go into the cat 150 and pick up the sum of the LT and RT and jumper that straight to the C output

Posted by Joe Schmidt (Member # 822) on 04-19-2001, 08:17 PM:

Gordon, if you're going to do that, shouldn't you have two isolation resistors as you're summing to channel C and you don't want to short L and R together as there goes the stereo. [?] With one channel of amplification, such as an opamp chip, and 10K isolation resistors you can sum

2.....50 channels without them interacting

and then also should be a gain control after the opamp as one might very likely want channel C a little softer.

Posted by Christopher Wehrman (Member # 806) on 04-19-2001, 11:04 PM:

Hellow All,

This is my first post here on Film-Tech. I have been reading the forums for some time now and thought that is was about time that I get envolved.

I run a 150 seat single screen theater w/ balcony. I have recently installed a mono system with front center, mono surround, and sub channels. We have a Ultra*Stereo JX5/95 processor with the left, right and matrix cards removed. I think that it is a decent system. I am very pleased with the sound and I think that it sounds just a good as some of the local multi-plexes in our area. We chose this system for it's price and our specific situation. Unfortunatly, we are not going to go digatal, at least not with the current owner .

This is just my two cents worth.
What do you guys think of U*S processors?

Posted by Richard Tucker (Member # 812) on 04-20-2001, 12:40 AM:

Paul;
It sounds as if you are toying with the idea of simply pumping the mono center signal to speakers hanging on the wall as well as behind the screen. DON'T DO IT! Therin lies the way to the Dark Side, Luke, and to some really lousy sound as well. You do not want the center channel to come from the walls as well as from the screen because you will have massive amounts of cancellation (auditory dead spots) in the auditorium. I have seen really cheepo installs where the mono center signal came ONLY from the surrounds, without a screen speaker, but it sounds pretty cheesy and flirts with the Dark Side. (I've even seen Left and Right pumped straight into a 2 channel preamp and out to the left and right surrounds for "stereo" surrounds. Ich!) You really need a processor to properly decode and delay the surrounds.

NOTE: if you are doing surrounds to try and improve poor auditorium acoustics, you may be disappointed with the results. Older theaters were generally much more live than new ones to give the performer/speaker more presence in the auditorium. Surround channels were developed to be put into relatively dead auditoriums so filmmakers could control that presence. Surrounds in a live theater usually clash with the natural acoustics and sound poor. I would strongly recommend improving your acoustics, perhaps just with some cheap wall covering, before spending money to upgrade you sound system.

Processors: as I recall, the Ultra and Kintek (and maybe some others) can be set up to put hard left and right channels into the left and right surrounds, if you configure your surrounds to stereo (this to make up for the lack of l and r speakers in a center/surround configuration). However, I have not been able to tell a difference between these faux "stereo" surrounds and mono surrounds. "Mono surrounds", by the way, usually refers to only one surround channel going to both walls, as opposed to "Stereo surrounds" which are discreet channels going to the left and right surround walls. (Don't get me going about Dolby EX.) All optical tracks have only a mono surround track, which is decoded from the L and R. Only digital has true discreet stereo surrounds. This means you can use any processor to get a center channel and a surround channel for optical (use L surround output usually for mono surrounds, although in optical L and R are the same), and most have a subbass as well.
Don't get a Starscope or a Starlet though, even if it is free! The surround threshold has to be adjusted for every movie, and will drive you insane.
Hope this helps. Good Luck!

Posted by Aaron Sisemore (Member # 145) on 04-20-2001, 12:49 AM:

>>Only digital has true discreet stereo surrounds.<<

In 35mm yes. There is a 70mm format (Dolby Format 43(??)) with discrete stereo surrounds as well.

Aaron

Posted by Gordon McLeod (Member # 33) on 04-20-2001, 08:44 AM:

Actually the Kintek did not put a hard Lt or Rt into the surrounds but comb filtered the mono matrixed surround output and then used a gain riding logic circuit to determin which side to favour
Joe there is no need of a resistor or opamp
If one looks closely at the Cat 150 D matrix the Sum appears at the input to the AGC circuit. It can be jumpered directly to the c output disconecting the logic output for C
this will provide a mono sum to the centre (in effect what a mono sound system will reproduce) and the properly decoded surround track to the surrounds without the pumping effects of summing the LCR output of the matrix
Also Eprad DSS can be configured to do this with jumpers as well and since it includes setable crossovers and monitor it does make a rather economical centre surround Biamp system that can be easily upgraded

Posted by Pete Naples (Member # 761) on 04-20-2001, 05:58 PM:

If it's a Dolby later than a CP55, how about using the H.I. output to drive the 'centre' and using the surround output as normal?? That'd save any modifications.

Posted by Paul Turner (Member # 832) on 04-20-2001, 11:18 PM:

Ok, talked to my equipment supplier and we're talking about a Dolby DP50 or an Ultra Stereo JB-2. We'll see were that goes.
I've had nothing but trouble getting the fire department to cooperate as far as wall coverings go (this could be a whole new thread). I'm going to tackle that one before installing any equipment. thanks again everyone! Paul

Posted by Gordon McLeod (Member # 33) on 04-21-2001, 10:59 AM:

If you use the HI output I don't know if the eq's will behave very well
as you would have to eq LC R all one at a time and then there cumulative effect

Posted by Steve Guttag (Member # 268) on 04-21-2001, 03:27 PM:

Gord:

I can't say my experiences concur with yours on this one but I do see you point. Fortunately, it hasn't come up with me enough to be definative on it. It is certainly possible to do as you say and pick up the Lt/Rt post NR and feed them to C and let the Cat. 150 do it's thing for the surrounds (kinda like Non-Sync format 60 but using C instead of L and R).

Others:

As to the Ultra Stereo JB-2....I'd stay away from it...it looks like a nice piece and has all the goodies built in but it has been VERY problematic for us. The CP-50 on the otherhand is a tank and can be outfitted as you desire...even all the way to holy-grail...Digital!

Steve

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"Old projectionists never die, they just changeover!"

Posted by Gordon McLeod (Member # 33) on 04-22-2001, 12:04 PM:

Steve I definetly concour on the US JB2 units being problematic

Posted by Paul Turner (Member # 832) on 07-12-2001, 11:01 PM:

Well, it's been about three months since I originally asked the question that heads this topic. Tonight I am running my first show with a Dolby CP55 Stereo Surround. I researched, designed, and built my stage speakers and hung my surrounds. Did all the hard lifting and cussing of the installation myself then had Joel from American Cinema come in and do the A & B Chain. Now, I keep getting up from my desk and peeking into the booth because the sound is so much better, it sounds like people are running around in there -- but it's the MOVIE! We start The Golden Bowl tomorrow, so we'll see how it does with the accents -- which is the main reason I did this. Thanks for all the input from everybody.