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Topic: Mono Surround Sound?

Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Joe Schmidt
Expert Film Handler

Posts: 172
From: Billings, Montana, USA
Registered: Apr 2001

posted 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.

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Christopher Wehrman
Film Handler

Posts: 15
From: St. Louis, Missouri
Registered: Apr 2001

posted 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?

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Richard Tucker
Film Handler

Posts: 15
From: Austin, TX, USA
Registered: Apr 2001

posted 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!

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 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

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Pete Naples
Phenomenal Film Handler

Posts: 1565
From: Dunfermline, Scotland
Registered: Feb 2001

posted 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.

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Paul Turner
Expert Film Handler

Posts: 115
From: Corvallis, OR, USA
Registered: Apr 2001

posted 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

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 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

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

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-22-2001 12:04 PM

Steve I definetly concour on the US JB2 units being problematic

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Paul Turner
Expert Film Handler

Posts: 115
From: Corvallis, OR, USA
Registered: Apr 2001

posted 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.

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