What condition delivers a good solid center channel signal on the optical track? Here's my understanding of the Dolby/Sansui 2:4 matrixing scheme, as used on movie optical soundtracks.
A signal appears on one of the two optical tracks. That sound is reproduced from the left (or right, as the case may be) channel only. When the same signal appears on the opposite track (only), the sound is reproduced from the other side of the screen. When on both, in phase, it comes from the center.
My question has to do with the level of this center signal ON THE FILM, as compared to individual striations of L-only or R-only signals. What are the optical track conditions that reproduce the center channel in the theatre, to the same level as a lone individual track (L or R-only) would at the screen?
Is there something in the encoding that raises the level or modulation of the L and R striations of the optical track that specifically steer it to the center channel?
Here's what I am observing. I have a track with two equal (in phase) signals which seems to come, not from the center channel in the theatre, but from the left and right speakers simultaneously.
This isn't a reproducer or processor problem, it's a print master recording condition that I'm researching.
Thanks!
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Better Projection Pays!
There is nothing encoded in the soundtrack striations to steer the sound. The front channel steering is entirely a matter of volume as you have stated. Identical L/R (in phase sounds) should be routed to the center channel. If this is not happening, either something is malfunctioning in your Dolby decoder or the stereo photo cell is out of alignment.
Gordon, does the .7 value refer to 70% below a L-only / R-only signal? That would explain why the sound appears to eminate from L and R simultaneously as it stands.
Thanks again!
-Tim
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Better Projection Pays!
Mark
Tim
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Better Projection Pays!
I just reread Tim`s post. It had slipped my intention that the soundtrack wasn“t encoded, but supposed to be mono. So there must have been a phase shift or slight level discrepancy when the sound negative was recorded. OK.
Still, what about the printmaster format?
The problem was noticed in an answer print.
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Better Projection Pays!
26 - printmaster 2-ch. no NR
27 - printmaster 2-ch. a-type
28 - printmaster 2-ch. SR
I had always assumed that these formats were intended for 35mm mag tracks to be played through an external preamp (MPU-1, perhaps) and then fed through the matrix/eq/output and, optionally, the NR stages in the processor. Thus, the only difference between, say, 27 and 04 (Dolby A-type) would be the input source (external mag. vs. optical preamp), correct? Or is there more to it than this?
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How did that happen?
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By the way, there is Dolby Surround Mixing Manual available from Dolby as pdf.
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Better Projection Pays!
Gordy, if the signal is encoded at equal level but with a 90 degree phase difference, the sound will appear in ALL channels at equal level. The matrix regards such a signal as "mid-field" so the steering is turned off. Addition (or subtraction) of 90 degree phase shifted coherent signals results in a 3dB loss, so all four channels will have identical output levels.
Small point I know but remember, accuracy! 
In fact there is no way to get simultaneous left only and right only signals from the matrix (anybody's). Only one channel can be predominant at any one time. So Tim's original post intrigued me because it would be impossible to achieve, even with some kind of error. But he has since admitted there WAS centre, it just wasn't HARD centre. Remember the word, Tim - accuracy!
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
I have met Gordy, in fact had lunch with him and I must say I have very high regard for the man. In my opinion he is a skilled, very knowledgable and competent cinema engineer. He is also one hell of a nice guy into the bargain. My comments are intended as lighthearted and friendly and I am sure Gordy takes them that way. If I say something that is not quite correct I would expect Gordy or anyone else to correct me, hopefully also in a lighthearted way.
I guess my references to accuracy are really aimed (subliminaly) at people who experience problems with equipment. Taking just a little time to accurately diagnose (and report) a problem makes finding a solution that much faster and easier. I often read Brad saying something like "please give us more information so we can help you".
I should also mention that Australians (particularly me) tend to have slightly different (possibly even bizarre) sense of humour, compared with those residing on other parts of the planet. It comes from living on the underside of the globe where the earth is above your feet and the sky is below your head. Think about it.
Ray
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But he has since admitted there WAS centre, it just wasn't HARD centre. Remember the word, Tim - accuracy!
Hi Ray, I thought I did describe it accurately. I've said all along that it sounded like it was coming from L and R, which it did. I didn't say it was coming from L and R. 
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In fact there is no way to get simultaneous left only and right only signals from the matrix (anybody's). Only one channel can be predominant at any one time.
I appreciate everyone's input and expertise on this, really. I think the 70% value Gordon cited for the C and S channels was the key. The mix was out of proportion.
Thanks again!
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Better Projection Pays!
Gordy I assume you are talking about the Cat110 Mono/Stereo optical card. Now that was very early in the piece and not a "real" matrix, more of an interim step, and a poor one at that. It used gain riding rather than addition/subtraction.
BTW the person that e-mailed me about Gordy has e-mailed again to say they were only joking. Sigh. See what I mean about differing senses of humour?
Ray
I know I saw nothing on Ray's comments to take offense at...particularly since they were not aimed at me!
The backward compatibility thing only goes but so far...the 110/116 days and those tracks if played back on modern decoders will not sound the same as if played back on original equipment. The L and R vs C only ducted a small amount to each other to keep a hard center dialogue.
Now if you mean backward compatibility in the sense that a modern film will "play" on old equipment, then yes it will play but will sound nothing like what they heard in the studio.
Steve
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"Old projectionists never die, they just changeover!"
As much as I love 70mm 6-track mag, I really do think that 35mm 4-track mag is an idea whose time has come and gone. I'm sure it was great in the 1950s and 1960s compared to mono optical tracks, but I genuinely believe that matrixed Dolby SR optical tracks sound better than the mag prints that I have seen. (Of course, that isn't to say that 35mm 4-track mag wouldn't sound better if done today with modern heads and NR systems, but I've not heard a 35mm mag print made after 1970 or so.)
When you get to be the age of Frank or myself, you don't even hear out to 12 KHz.
(Gone are the days when I heard the ultrasonic detectors used for traffic lights, harmonics from an ultrasonic film cleaner, or the high pitched whine of flyback transformers). 
Flying small airplanes, high fader settings, and using a two-cycle rototiller in my garden without ear protection have evidently taken their toll.
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Besides, a properly designed matrix in a correctly aligned system can fool probably 95% of a cinema audience into thinking they are listening to a discrete playback. It is only when the system malfunctions or there is an alignment problem that the conjuring trick is revealed.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: here
The main reason when why Quadraphonic Sound faltered and Dolby Surround was so much more successful, even though Dolby actually used the Sansui VarioMatrix in their early prototypes, was because by the time Dolby was perfecting their 4 channels born out of 2, delay had become fairly inexpensive and could easily be integrated into a surround channel.
In the early 70s it was a different story -- digital delay was much to expensive to incorporate into consumer Quad products. And it is the use of time delay in Dolby Surround that is the "still point of the turning world"....that one all-important ingredient that made Dolby Surround actually sound like distinct surround. It's the aural illusion that Quadraphonic Sound simply didn't have. Without time delay, Quad, even under the best situations, was not much more than "full ambiance," a kind of circle surround rather than the ability to create locatalized rear positions (be it illusion or not).
Rather than a monumental leap into new technology, Dolby's 4 channel Cinema system was actually more of an briliant integration of long existing technologies: 1) Sansui's VarioMatrix, Type II from the Quad era 2) the application of time delay to make use of the Haas Precedence Effect and 3) Dolby's own Type A and Type B Noise Reduction that was already well established in recording studios and consumer products for a number of years, 4) the splitting of the bilateral optical stripes that had been carrying a mono channel for years on 35mm film, into dual channels and lastly, 5) third octave room equalization, pionered 8 years before by Altec Lansing in their "Theatre Voicing" system. None of it new or earthshaking, but put it all together with refinements in each, add a few format switches, a slew of CAT numbers and voilą, the optical answer to mag.
Granted, I am oversimplifying and certainly not disparaging the great contribution of the Dolby's bilateral stereo optical recording/playback system for 35mm film -- it gave us real stereo in what had much too long been a mono celuloid world -- in all the other media, stereo sound was well established in FM, consumer records and tapes, and accepted as superior by the public. Dolby finally made it cinema's turn, except that cinema had been doing it since FANTASIA, THIS IS CINERAMA, OKLAHOMA! and THE ROBE....eveyone just forgot how breathtaking it sounded back then with those discrete mag tracks.
For a kid who thought stereophonic sound was the most incredible thing he had ever heard -- magic for the ears that he couldn't get enough of, the death of 4 trk mag was a great, great disappointment. For me, Dolby Stereo never quite measured up to the same excited as much as those old 4 track mag prints.
Frank
God, how that used to drive me insane. I would be running around the theatre like a mad man during testing, yelling to the rest of the crew, "Doesn't anyone HEAR that damn tone?" (this after installing 20db attenuation super expensive notch filters on all 4 channels -- I STILL could hear it!) Those who frequented lots of Van Hallen and Zepplin concerts without ear protection only heard silence -- ah, the blessing of cochlea abuse.
Actually most of the studios other than Fox abandoned the track 4 12kHz tone quite early on -- we played many mag prints that had what we marked down on the projection report as a "clean surround track;" i.e., no trigger tone. The clean trk 4 was so prevelant that I installed a Fairchild "ducking" unit that was made for the recording studio to deal with the prints without a tone. I had to rip out the relay because it would not play the surround track if no tone were present. The Fairchild unit solved that problem.
It was a very small unit that simply used the audio itself on channel 4 to either pass the signal without any attenuation as soon as it "heard" audio of a set amplitude or it would "duck" it down by 20db when the audio dropped below a preset level. It also had a release setting that allowed it to gently reduce the channel when audio stopped. This worked perfectly for surround tracks with both trigger tones or without.
I agree that mag's time has come and gone; with the advent of digital, the issue of the Dolby analog system limited by its lack of discrete channels is gone. And yes, I will even agree that a well aligned SR system can sound very good, but that means almost always having to mix dialgue in the center and always being afraid of sounds that are by accident out of phase in the recording session winding up zipping around in the theatre to somewhere that they are not supposed to be.
There is a funny story about exhibitor execs who had watched a roadshow in 70mm and then saw the same title again in 35mm SR. They were all upset and wanted to know why the 35mm sound had a lot more music coming out of the surround channel than the 70mm presentation. It was difficult to explain that what they heard coming out of the surrounds in the 35mm optical version was simply natural phase varients that the matrix interpreted as out of phase and hense surround audio. They would rather have the errant matrixed sound than the truer discrete sound -- the old idea, "Hey, kid, I paid good money for those damn surrounds....I better damn well hear them."
My contention is that mag shouldn't be judged by the limitations of the 50s and 60s, but think of what could have been, had the refinements of more recent advancements in low noise, high output tape oxides, low-noise circuitry and high resolution head construction were applied to the mag concept. However, even if we could timeshift it all, no matter what, the window for mag was relatively short and digital has closed it pretty much for good. Forgive me if no matter, I still lament its passing along with movie palaces and mom & pop neighborhood theatres.
Frank
Matrixing of 4 channels for a two channel media (4-2-4) was invented by Peter Scheiber, a New York musician. He filed a patent (#3,632,886) titled "Quadrasonic Sound System" on Dec 29, 1969. In that patent he discloses a four channel system with a speaker directly in front, one either side, and one behind the listener using L+R and L-R (-3dB) encoding/decoding. He also disclosed a logic steering system to increase separation.
He lodged another patent in Jun 1970 which disclosed an option to swing the speaker array around by 45 degrees to produce a left front / right front /left back / right back system using the same encoding techniques.
In July 1973 he filed a third patent with improvements to the steering circuits for the original system.
Sansui and friends came along after Scheiber with the idea of a 90 degree phase difference between the rear channels. It was an idea that gave very poor separation (even with steering) and was destined for failure. However a US company Tate, did develop an analog chip set (two LSI chips) to improve separation for quad systems in general. It used a combining network, rather than gain riding for the logic steering which was a huge leap forward.
Dolby licensed their original matrix from Scheiber. Sansui had nothing to do with it. The first really successful attempt by Dolby at a matrix decoder came in the form of the Cat150 which used the Tate chip set in the steering circuits. It also used delay for the surrounds but it was NOT digital, but in fact a bucket brigade analog system. The digital version, which was initially made by a third party company (Delta Lab), came much later.
The modern Dolby pro-logic system still uses the Scheiber matrix and (a refined version of) his steering circuits, enhanced by (a refined version of) the Tate combining network. AND Dolby have managed to re-patent it at least twice. Go figure.
One improvement Dolby did make (in addition to adding surround delay) was to phase shift the surround channel by 90 degrees in the encoder, to decorrelate the rear channel from the front channels for front-to-back panning. Without that phase shift, a front to back pan would cancel out in the right channel at mid pan. So the pan would go round through the left speaker rather than down the middle.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
The reason it stuck out in my mind was that we had the Sansui encoder and decoder units in our recording studio, so when I saw mention of it in the piece I was reading, I remember thinking, gee, quad makes a comeback. And I also recall that the Dynaco amp people had put out info on how to get a kind of poor man's ambiance surround channel by using the +L & +R terminal on their amps to get a L-R signal for the rear speaker. Seems like everyone had a way to get Quad at the peak of the craze -- Sony's SQ, Sansui's QS (talk about confusing the consumer) and lots of component manufacturers making receivers with decoders built in with four channels out. I recall Lafayette Radio --folks on the East Coast will remember them -- had a flyer that featured nothing but Quad gear. It was quite an exciting blip on the audiophile timeline.
I would also like to say that I respectfully disagree with Ray that the Sansui matrix had bad L/R separation. Perhaps their prototype or first generation might have, but the Type II certainly didn't. I recorded many a master tape with that unit and one of the things I was always most concerned about, being a two channel stereo recording engineer first, was that no matter how any new-fangled matrix system was going to get rear channels, it couldn't compromise my front left and right stereo channels. I did classical recordings for a Conservatory of Music of uncompromising, many times b-busting musicians -- before we moved to any new Quad system, we were all adamant that it had to leave L/R untouched; it had to keep a robust front stereo soundstage. We did lots of listening sessions with conductors, composers and musicians in the studio who were hyper- critical about the evaluations of the new quad gear. We even did a few dual recordings with two decks, one recording standard two channel stereo and one recording with the Sansui matrix. The challenge was to do an A/B test between the two channel recording and the matrixed recording but only playing the Left/Right output from the decoder, to see how left/right alone sounded. Although we did hear some slight differences, mainly in amplitude of the phantom center, Front Left/Right from the decoder maintained a well defined soundfield; it was airy and certainly didn't collapse, even when reproducing difficult program material, like solo instruments at the extreme left or right. My studio also released an LP recorded with the Sansui matrix -- an original cast recording of a musical, "Rubber Nickels." I can send you a copy and you can tell me if there isn't excellent L/R separation.
As for Dolby's modification to the matrix, well, all I can say is that in the early days of Dolby A and the first 150 cards, techies had a name for the Dolby system -- Front/Rear Stereo. Mind you, I didn't make that up -- lots of people felt that Dolby sacrificed front Left/Right separation for getting good Front/Rear separation. I never did any kind of tests to prove or disprove this perception, but it certainly was out there.
In fact, at one of the SMPTE NY Section meetings at the dawn of SR-D, Dolby demonstrated what the matrix does with difficult material. They played four different sound....a flute, a piano, a man speaking, and car motor. First each sound was played separately, each coming successively from one of the five locations -- Left, Center, Right and Rear. The matrix was able to place each in approximately the right place as long as they were sounding solo. Next they started with the left channel sound, then added the next in the center, and so one until each sound was playing in its channel simultaniously. As the sounds were added, the soundfield collapsed to what can only be described as a mono sound coming from the center of the room. Next the same sounds were played in Dolby SR-D to demonstrate that with discrete digital, the sounds stayed right where they were supposed to be. No surprise. The point is, although Dolby was all about demonstrating how impressive their discrete digital system was, it certainly made very clear the limitations of the matrix system as well -- kind of like sacrificing SR for the sake of the new Big D.
Forgive me if I can't resist saying that, hey, if you did the same demo with the 50's 4 trk mag technology, the sounds would also have stayed rock hard in each of the channels too!
Frank
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one of the very first technical reports that I saw about the then new Dolby optical stereo system mentioned that they did use the Sansui configuration,
I'd always heard Sansui, too. Which is not to say they invented it.
(Hiya, Frank!)
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Better Projection Pays!
For the cinema matrix, the theoretical left/right separation is the same as for a normal stereo recording and can be up to 60dB or more. Also the separation between centre and surround is of a similar magnitude provided there are no level or phase errors in the signal chain. However the separation betwen left and centre, right and centre, left and surround and right and suround is only 3dB, which is why we need a steering system.
The SQ and QS systems suffered from similar limitations. The separation between either front channel and either rear channel was 3db (or less). At least with the cinema matrix you can get great separation in two axes, whereas with SQ and QS quad it was only possible in one.
Now Gordy my friend, which Sansui phase shifting chips are you talking about? What was their part number?
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
quote:
Beginning with A Star Is Born and ending the Spring of 1979, Dolby SVA prints had surround information encoded using the Sansui QS Matrix, in addition to techniques designed to reduce crosstalk from the front speakers. The center channel had been derived by a logic circuit which analyzed the differences between the left and right track signals. Separation between channels was of the order of 6 to 8 db.Hair and Hurricane were the first films to be mixed with a new "center channel and surround derivation card" which allows much greater separation between channels.
Certainly I have never come across any evidence that any QS DEcoders were used. Some people have confused the Tate chips on the Cat146 with Sansui because these chips were originally designed for use in quad decoders (for Fosgate I think). I am curious about the Cat116 card that Gordy mentioned. I have never seen one. Was this something that popped up between the Cat110 and the Cat146? (Dolby have more cat numbers than a big city alley-way).
I guess when you think about it you could say that the cinema matrix contains elements of both Scheiber's matrix and Sansui's matrix, in the sense that the Scheiber matrix has a centre channel but no use of 90 degree phase shifting for the rear, and Sansui's matrix has no centre channel but does make use of opposite 90 degree phase shifts for each of the rear channels, resulting in a nett 180 degree phase difference for a centre rear encoded signal.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
The Cat. 146 was one half of the Cat. 150 system. The reticon delay board was the other half (on the first generation).
Steve
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"Old projectionists never die, they just changeover!"
I don't recall if the Sansui chip was used or not. EPRAD did use a Sansui chip on their STARSCOPE unit. I look into the Cat. 116 and get back to you.
Steve
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"Old projectionists never die, they just changeover!"
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"Old projectionists never die, they just changeover!"
Of course this doesn't change the fact that matrixing was indeed invented by Scheiber, if fact those patents of Sansui's that were filed in the USA (most were only filed in Japan) reference Schneider's original patent. Sansui simply added the phase shift as a different means of providing two rear channels. If you go back before Scheiber there was a guy called Rogers who filed a patent for a derived centre channel in 1961, but this was a playback only arrangement and quite different from the encode/decode matrix systems that Scheiber invented.
Dolby's own encoder (used in the DS4 etc) works very differently from the QS encoding scheme, in that it uses a single 90 degree phase shifter in the surround channel and then applies this signal in phase to Lt and in antiphase to Rt.
One other tid-bit of useless information - QS was also known as RM and was very similar to Sony's SQ system. Anyone interested in the details of these two sytems can refer to a US patent 4,021,612 which descibes a decoder suitable for both systems. You can view this patent by going to here and typing the patent number into the search engine.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
THere are about 12 I know of still in use in the Toronto area 2 are in SA2 adapters with CP100 ther rest are internally in the cp50's
BTW I mentioned above "Sony's SQ" system. In actual fact the SQ system was developed by CBS, however Sony was probably it's biggest promoter so SQ came to be closely associated with Sony.
Michael Schaffer mentioned he heard there were three competing quad systems. In fact there were at least four commercial matrix arrangements - SQ, QS, EV Stereo-4 and Dynaco. There was also a four channel discete disc format called CD-4 developed by Matsushita.
I must apologise to Frank for my correction regarding Dolby's use of the Sansui matrix (in the early days at least). None of us has all the answers and one of the great things about this forum with it's many knowlegable contributors is that between us we can usually uncover the whole story.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
Frank
Just as a footnote to all of this, Steve Guttag kindly sent me a copy of the schematic for the Cat116 card. As predicted earlier, the left back and right back outputs of the QS matrix are indeed summed for the single channel required for the cinema matrix. In fact the QS system (as one would expect) is significantly modified by Dolby to achieve the required characteristics for a cinema adaptation. Looking at the schematic one can see how the Cat150 evolved from those early beginnings. Interesting little segment of history.
Christos.
In retrospect I should not have mentioned the Cat116 schematic as I did not want to give the impression that Steve (or anyone else on this forum) hands out the schematics of other companies willy nilly. All companies, inclduding my own, are very protective of their intellectual property and normally only supply schematics to those that have a legitimate need and are known and trusted. In this case the document could be considered historical in nature, and knowing that I would not use it for any purpose other than historical interest is why Steve sent it to me.
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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
However, in the interests of this thread...there was nothing like the schematic to end the "Debate" about the whole "Did they or didn't they use the Sansui QS technology in the development of the Dolby SVA evolution".
Steve
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"Old projectionists never die, they just changeover!"
