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Author Topic: Film sound - history and technical details Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-17-2004 03:08 AM                     Wow, I totally learned something. I always thought that "bilateral" referred to the fact that there are two tracks. I didn't know it actually meant that there are two edges on each track, and dual bilateral means two tracks. So let me see if I understand this. The original variable area tracks were unilateral. Then it was decided to come up with a bilateral track for redundancy? Quite interesting. Now that some of you have confirmed that such older tracks are playable on today's readers, my question is, How? Wouldn't the solar cells have to be different, and/or wouldn't the processor have to treat the tracks differently? On a related note, do today's readers contain one solar cell, or two (one for each track)?  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 07-17-2004 03:29 AM                        since even the (non-dual) bilateral mono tracks have bilateral symmetry (duh) each half may be read in the conventional manner as one channel with no complications, and processed as mono. the unilateral track will probably not work this way. at the very least, the center of the track, which contains information, would never get scanned. it would be interesting to hear it. it might well be somewhat intelligible, but sound awful. i have a roll of film with a unilateral track. if it's not too shrunk i might try to play it (with the lamp off!). carl  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 07-17-2004 03:33 AM                     The stereo cells in my Prevosts really looked like 2 individual cells, there was no mistaking it. But the ones in the Centurys looked like one smooth, continuous chip. Looks aside, there have to be two separate cells for stereo. I don't know exactly what goes on in the LED reverse-scan readers.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 07-17-2004 08:18 AM                        Years ago I saw a 16mm print that had a soundtrack with SIX lateral traces, although lateral seems a superfluous term when it comes to soundtracks (aren't they ALL lateral tracks?). It was so unique that the title stuck in my mind to this day....it was used on the Bell science series -- one was about blood, another about weather, etc. I think there may have been 4 or 5 titles in that series and all were released free through non-theatrical houses like Sterling Films and Modern Motion Pictures. I believe they were IBTech too. But the prints had tracks with this very unique mulitple configuration. From as far back as when I first started running 35mm in the 60s, the vast majority of soundtracks were dual mono. Since I started off as a sound engineer, I was quite enamored of stereo sound and I couldn't understand why you couldn't simply use those two tracks to record left and right information instead of redundant mono tracks. A friend and I actually went to the patent office to see if anyone had patented a stereo variation of the long established dual track. I was convinced there was no reason why you couldn't get stereo out of those two soundtrack traces. How right I was, eh, Mr. Dolby?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-17-2004 08:24 AM                     The 16mm scope print that used to be incirculation up here of Ben Hur had 6 optical tracks (all the same)  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 07-17-2004 09:46 AM                     J.A.Maurer optical 16mm film recorder was the source of those 6 track variable 16mm tracks. Their reasoning was to decrease distorsion ( 2 - 5% was normal for 16mm sound tracks ) and to increase fidelity. Tests where done in the U.K. in the late 1930's using left right stereo on 35mm V.A.optical. I remember viewing the prints of these of an approaching train and an anounncer on a stage walking around talking for the stereo track. Dolby introduced the noise reduction aspects but could not "patent" the track due to the prior experiments.  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 07-17-2004 06:11 PM                     Ken wrote: quote: Ken Lackner Now that some of you have confirmed that such older tracks are playable on today's readers, my question is, How? Wouldn't the solar cells have to be different, and/or wouldn't the processor have to treat the tracks differently? On a related note, do today's readers contain one solar cell, or two (one for each track)? To answer the second part first, a stereo optical head has two cells, a normal mono head has one. A push-pull mono head has two. A normal mono head can play any type of optical track, except a push-pull one. The cell is measuring changes in the amount of light transmitted through the track; it doesn't matter if these changes are caused by variations in the density, or the area of the track, nor what shape the clear area of a variable area track is. If you play a stereo stack with a mono head, the two tracks will both be scanned, and combined, to form a mono signal. If you play most types of mono track with a stereo head, both cells should receive the same variations of light intensity, since each half ot the track is the same, and will therefore produce the same output. With the processor operating in mono mode, the two inputs will be combiined, and fed to the centre channel only. If you switched the processor to stereo, the decoder should see the same signal on both inputs, and therefore send it to the centre channel, but there will be some bleed-through to the left and right channels. If the sound head is mis-aligned, the signals may be out of phase, which would also result in some sound being heard in the surround channel. Playing a unilateral track with a stereo head will result in a rarrow area down the centre of the frack not being read, and this should result in some distortion. When I was at the Loew's Jersey in Aprin they ran a cartoon which had a unilateral track. They have a stereo sound system, and it didn't sound too bad, but then a track that old isn't going to sound very good, by modern standards, anyway. If you managed to find a print with a push-pull track, and played it on a normal mono head, you would get almost no sound, as the two halves of the track are opposites to each other they wouln cancel out, resulting in no sound. As Leo has pointed out, it was Alan Blumlein who produced the experimental stereo tracks in the '30s; I think it was in 1935, or 36. Some of these recordings survive. Alan was working on stereo sound, not on film as such, he used film because it was able to carry two tracks, the idea of using the two walls of a groove in a disk for this purpose hadn't been thought of then. All of the films which I've seen do however carry some sort of picture. Most of the recordings simply feature technicians in white lab coats walking across the screen counting, but I have seen one of part of an amateur dramatic performance. Alan was killed, at a relativly early age, during the Second World War. Alan's work on stereo sound recording was purely experimental, but there was an attempt to revive the same idea in the '50s, under the 'Photo Stereo' name. I'm not sure if any films were actually released at that tiime. Both of these systems were purely two channel, there was no matrix encoding to provide a centre channel. At this time, projectors were using glass vacuum tube photocells, and there was a double version available, with the two cells inside a single glass envelope, intended for reproducng push-pull tracks. Some projectors were designed to use these, though push-pull tracks never came iinto widespread use for release prints. Any projector equipped with such a cell could have been used for stereo sound. I can think of a number of practical problems with the idea, but did anybody ever propose a system which recorded three channels of stereo sound, using the three layers of colour print stock?  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-18-2004 01:44 AM                     Thanks, Stephen, that was quite informitive. What are push-pull tracks?  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 07-18-2004 03:20 AM                     They are tracks, normally mono, which come in two parts, one being the exact opposite of the other. In a variable area track, where one half of the track is wide, the other half is narrow. With a variable density track, where one half is light, the other half is dark. If you were to play them with a normal mono head then the two halves of the track would cancel out, and you would get no sound. They had to be played with a split photo cell, like a modern stereo track, one of the signals was then inverted, and the two siignals then combined. The idea was that it reduced distortion. There were release prints made with them, but they were never generally adopted. The problem was that they would have needed modifications to the soundheads in all the theatres. I've seen an advertisment for a projector, BTH I think, from the '40s which said that it could take the double photocell for push-pull tracks. I've never seen even a single frame of release print with a push-pull track, but there are some pictures on the BKSTS wallchart. It was a bit like CDS digtal tracks, few theatres were ever equipped, few prints were ever made, and the idea was dropped. Many years ago I did see a pair of ancient projectors which were still fitted with the double photocells. Where push-pull tracks were more widely used was in original recording, before the introduction of magnetic recording. For this purpose, since there was no need for a picture on the same film, double-wiidth tracks were sometimes used. There were three types of push-pull tracks that I'm aware of, variable density, and two types or variable area, one was a duo-bilateral type, the other was based on the duplex track, which there is a picture of in the 16mm examples which I posted. In the push-pull version, the central black area would be a constant width, but would move from side to side, giving the complimentary tracks on either side. This was known as a 'snake track' Disney's Fantasound system used four double-width snake tracks, three for audio, and one for control tones, on a single strip of 35mm film. There is a picture of this in one of the Fantasound documents in the American Widescreen Museum www.widescreenmuseum.com I also seem to remember that at about the same time as Dolby Stereo was introduced there was a proposal for a system using multiple, wery narrow, snake tracks, but it was never adopted.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 07-18-2004 04:11 AM                        quote: Stephen Furley did anybody ever propose a system which recorded three channels of stereo sound, using the three layers of colour print stock? Yes, John Mosely (sound designer of Quintaphonic Sound for TOMMY) designed a multichannel soundtrack based on the three emulsion colors, each color recording a single channel. It had many drawbacks as the track had to be illuminated quite brightly because filters had to be used to separate each of the colors, with each filter depleting the amount of light available to the cell. Increasing the exciter lamp intensity caused other problems with flare and distortion. John P. may have an SMPTE white paper reference on this system, which I believe was called KenTech, or perhaps that was Mosley's company, I am not sure. But my recollection is that the company did produce a working prototype, and may even have printed a few test reels of a stereo feature with the system but, unfortunately for them, Dolby was working on its system at pretty much the same time and trumped the KenTech color approach. The really interesting thing about the KenTech colour approach is that it would be able to contain a DESCRETE surround channel rather than a matrixed one. The only processing that would be necessary would be to sum the left and right channels to derive a phantom center. But the surround would be a channel all its own, which means the sound mixer would have the latitude he had with magnetic sound and now again with digital, and that is, he has a much greater latitude in placing dialogue anywhere he wants across the stereo soundfield without worry of it swinging around into the surrounds. Once again he could mix directionally for dialogue placing the voice with the image as was the practice with almost all the 70mm multichannel mixes. Here's a question: years ago I recall that around the time Dolby introduced it's optical stereo sound, there was a rash of 16mm projectors that came on the market touting stereo sound capability. Evidently they were able to play SVA tracks, if such things were produced. I spoke to Ray Swank at the time and asked if any of the studios were releasing their 16mm titles with stereo tracks. He said there was never any move in that direction. Yet, I knew a projectionist who worked at the army base theatre in Fort Hamilton in Brooklyn and he said that when the army stopped acquiring their films on 35mm and went to 16mm, they installed a Dolby CP50 and I believe he said an Elmo pedestal projector; he also insisted that the 16mm prints that were set to the base were stereo prints and they were encoded with surround. He said they had [STEREO] printed in the soundtrack just like 35mm prints and you were supposed to selected Format [04]. Now these may have been prints especially struck for the army (the armed forces network bought all their own prints), but I have never seen a bilateral stereo soundtrack on any 16mm print. Has anyone else? I would think that if such prints were struck, they would eventually wind up in the hands of collectors, but I have never come across one. I also don't understand that if stereo encoded soundtracks were viable for the army, why wouldn't the studios just use the same sound negatives for the non-theatrical market? I have a feeling this is a reel myth. BTW, the KenTech colour stereo system would have worked as well on 16mm prints.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 07-18-2004 09:01 AM                     Colortek was the system and I heard the demostration in the early 1980's at a Los Angeles SMPTE convention. It was excellent. The conversion was installed in a standard Century soundhead. Concern about film processing issues and the push to Dolby Stereo analog tabled the system.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-18-2004 09:10 AM                        The analog tracks probably filled the whole space available on the film, so I guess that might have made up at least partially for the light loss described by Mr Angel. But I guess it wasn't compatible with conventional playback systems at that time, be it mono or Dolby Stereo. So that must have made it even more unlikely to be introduced widely.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-18-2004 10:51 AM                     The navy also had several theatres with Elmos and Prevosts with stereo cells connected to CP50's and KT800's AMC attempted a 16mm program with eastman 25's and Kintek systems as well  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-18-2004 12:15 PM                     Stephen, There were three articles that I could find on Fantasound at the Widescreen Museum. None of them had a pic of the actual soundtrack. Do you have an exact link? If modern cinema processors contained the right format, could they play a push-pull track on today's split cells? I don't see why that would have held back the implemenation of push-pull tracks, because obviously soundheads had to be upgraded once dual bilateral tracks were introduced. I just looked at all your pics on the 16mm thread. ( Link in case anyone else is interested.) Very interesting! Would each of these formats require a different soundhead modification? That must have gotten expensive. I never realized there were so many different types of variable area tracks. I thought they always looked like the tracks we have today.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 07-18-2004 04:41 PM                    Comtrak circa 1981 used a set of snake tracks to carry discrete LCR alongside an Academy mono track that is about the size of a single trace of conventional dual bilateral tracks. By "snake" we mean a clear line against black which varies in position--that is, it wiggles around, but does not change in width so does not have an effect on mono playback on conventional soundheads (they would have to turn up the fader not unlike what happened with the mag/optical track where the C channel mag stripe overlayed half of the optical track). Playback would be via a CCD scanner. Just outside the area scanned by a normal soundhead on the picture side was a straight line which acted as a reference point for playback of the snake tracks (counteracting film weave going through the soundhead or during printing). Beyond this beside the picture was a surround track which could be either a snake track OR something resembling a bilateral track but with differing sides for spit surrounds with modulation in the form of sum and difference. (Add the sides for Left Surround, subtract for Right Surround). Finally, on the outboard edge of the track (and again, outside the normal pickup area) was provision for a PCM data track. Description based on article in SMPTE Vol.90 Number 9 (September 1981), the same issue which described the Dolby CP200.  |  IP: Logged

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