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This topic comprises 5 pages: 1 2 3 4 5
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Author
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Topic: Film sound - history and technical details
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-18-2004 07:16 PM
Ken, I can't find the picture I was thinking of, I'm fairly sure it was in the Widescreen museum somewhere, I remember that it had that mottled look of an old wet-toned electrostatic copier that the other Fantasound documents had. There's so much information in there, it may have been in another article, one not just about Fantasound.
I've found another picture of the sound film, it's not as good a picture, the film edges and perforations are obviously drawn in, but I think the tracks are genuine, though touched up somewhat. Anyway, it gives a reasonable idea of what the track looked like. The left-hand track is the easiest to see the detail of.
This picture was taken from the booklet which Dion Hanson produced to acompany his 'Fantastic Formats' lecture. I hope he doesn't mind me using it. (Excellent lecture, Dion. ![[Smile]](smile.gif) )
Those pictures in the 16mm sound formats thread are only some of the more common formats, there have been others, though most of them are fairly minor variations of one of those shown. The various push-pull tracks, and something called a density squeeze track are the main missing ones. The density squeeze track was a variable density track where the width of the track was reduced during quiet passages, as a form of ground noise reduction.
All of the tracks shown can be played with a standard optical sound head, without requiring any adjustment.
You wrote: quote: Ken Lackner
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.
A modern stereo soundhead could play a push-pull track, if it was one of the standard width types, in the standard position on the film; it couldn't play a double-width track, for example. Because the two signals are 180 degrees out of phase, a stereo processor should send all of the sound to the surround channel. It would have been simple to provde push-pull as a format, with the sound being sent to the centre channel. The reason it wasn't done is that few release prints were ever made with these tracks, and none had been produced for several decades when the first Dolby cinema processor was introduced. If somebody had a push-pull print which they wanted to play, it would not be difficult to make up a card with a few components on it to fit in place of the Cat. 150 decoder in one of the older processors, as has been done to play Perspecta tracks. I don't know if the CP-650 could be programmed by a user to do this, I'm sure that Dolby could write the software to do it, but I doubt that anybody has ever wanted to do this.
I don't understand what you're saying about upgrading soundheads; no upgrading was necessary to play Duo-bilateral mono tracks. An upgrade to a double photocell would be required to play push-pull tracks when they were introduced, in the late '30s, I think, and a similar upgrade was requiired to play stereo tracks, be it the experimental ones in the '30s and '50s, or the Dolby ones in the '70s. A stereo push-pull track was never used to the best of my knowledge, with the single exception of Fantasound. It would have been technically possible, but a two channel system would have needed four photocells; Fantasound needed eight. Photocells were big glass vacuum tubes in those days.
Remember that push-pull basically uses two tracks to carry one channel of sound. When Dolby introduced their stereo optical tracks they wanted to use as few tracks on the film as possiible, to avoid problems with reading very narrow tracks; hence the matrix encoding, to get four channels onto two tracks. They would not have wanted to increase the number of recorded tracks by using push-pull. They also wanted their tracks to be compatible with existing mono equipment, to avoid dual print inventory problems and costs. They always stated this as an important advantage of their system. If they had developed a stereo system using push-pull tracks, this would not have been possible.
I mentioned push-pull tracks beause I thought it was necessary to give a technically complete answer to the questions of how many photocells are needed to play a mono track, and whether all types of mono tracks can be played without modifying the soundhead. Fantasound is historically interesting, but it was used on only one film, and I think only about six theatres worldwide were equiipped to show it. Mono push-pull tracks were somewhat more wiidely used than this, but only a few prints of a few films were ever made. Even for orgiinal recording in the studos, where it was more widely used, push-pull died out about fifty years ago, when it was replaced my magnetic recording.
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-19-2004 01:28 AM
Assuming that you're talking about normal mono tracks, no. it doesn't matter how many lines there are in the track, the mono sound head has just a single photocell, which measures the total amount of light coming through the track. This applies just as much to the 16mm tracks I posted pictures of with six or eight lines, still only one photocell needed. The only tracks which need two cells are stereo ones, though they can be reproduced in mono with a single cell, and push-pull ones, where two cells are essential, you would get no sound with a single cell. Since most people are never likely to see a push-pull track, for all practical purposes, any track can be reproduced with a single cell, though stereo tracks will only be heard in mono. With the exception of the eight line one, none of the 16mm tracks were uncommon, and almost all were used on 35mm as well. It's only in quite recent times that the duo-bilateral type has become universal. Several of these tracks were still in use in the '70s, and I think all were in the '50s and possibly '60s, though the unilateral type was rare then. Duo-bilateral tracks existed in the '30s, there was a long period when many types of track were in use. If you were to run a '50s film, it could have almost any type of track on it, and no adjustment or modification would be needed to play it.
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 07-19-2004 02:38 PM
quote: Frank Angel
John P. may have an SMPTE white paper reference on this system
Colortek Optical Stereophonic Sound Film System, John Mosely, SMPTE Journal, April 1978, Volume 87, page 222
Quintphonic Sound, John Mosely, SMPTE Journal, January 1977, Volume 86, page 20
I had the pleasure of knowing Mr. Mosely for years before he tragically died in a crash of his private airplane.
http://www.widescreenmuseum.com/sound/colortek01b.htm
quote:
The Colortek Optical Stereophonic Sound Film System
By JOHN MOSELY, KEITH O. JOHNSON,
and DAVID E. BLACKMER
Colortek is an optical sound system rendering four separate unilateral variable-area audio tracks and a central control track, all within the area of the present monophonic variable-area and variable-density soundtrack location as defined by American National Standard PH22.40-1967. The innovative design of the system employs, as a sound reader, a charge-coupled-device scanner (CCD scanner) and applies video technology to the read-out of soundtracks. It scans the four soundtracks transversally at 10 MHz, resulting in a CCD frame rate of 40 kHz, as the tracks pass longitudinally at the normal speed of 24 film frames/s (457.2 mm/s) through the sound reader. The electronic drive of a Westrex light valve has been modified to obtain the new soundtrack configuration. No ground-noise-reduction device or circuit has been incorporated, because the design of the CCD scanner suppresses ground noise almost completely. The soundtrack may also be reproduced on projectors with a normal optical sound head. However, due to the use of electronic companding and to the lack of ground-noise suppression, the reproducing electronics should be modified to reproduce the four-track format correctly. This format can be reproduced monophonically as well as stereophonically. Both the frequency and dynamic ranges of the recording light valve have been extended to achieve faithful transfer from the magnetic to the photographic printing medium and faithful reproduction in the theater. By the use of matrix encoding, the system can be extended to accommodate six separate channels of sound for surround sound effects in 35mm theatrical presentation. The narrow center control track serves several purposes: (1) it enables the CCD scanner to recognize and compensate automatically for any side weave of the soundtrack; (2) it serves as an image-spread monitor for correcting, within limits, distortions caused by image spread; (3) it can be used to trigger special sound effects or auditorium speaker groups as encoded on the control track; (4) it also can be used for automatized general theater operation. A specially designed compander completes the system.
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Martin Brooks
Jedi Master Film Handler
Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002
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posted 07-21-2004 12:12 AM
quote: Peter Mork
On the subject of tracks that used emulsion colors to separate channels, I remember reading somewhere that Popeye (1980) used a system of that sort. The only reference I could find via Google was a note that this film was the first release in Vistasonic sound, but didn't describe what it was. Anybody know?
I have a note in some documentation I have, but I don't remember the source. But it does say that Popeye was released in Vistasonic, a system developed by Paramount, but that it was a 4-track mag system. I don't remember why that would have made it special, especially since there were plenty of 70mm 6-track releases in that era and obviously Cinemascope used 4-track mag. I remember seeing the film in that format either at the old Loews Orpheum in NYC, when it was still a twin or at the Beekman...can't quite remember which. I do remember the sound being quite good. My notes do say that it played at five theaters in that format in NY, Los Angeles and Chicago. Larry Blake also mentions it in his article, "Mixing Dolby Stereo Film Sound" in the 2/81 issue of Recording Engineer/Producer (vol 12/#1)
Around the same time was the Kintek COMTRAK system, developed by John Mosley, which featured (in addition to Academy Mono) L-C-R-Surround, a command track and a locator track, but it required a CCD reader. The command track could be used to store low frequencies encoded in frequency modulation. Not sure if that system was ever used i a commercial film.
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-22-2004 01:07 AM
Do you know if the 'L' track, for example, was actually that, or a difference signal, (L-mono), similar to the way that component video is done? I have read articles which suggest both; maybe they tried it both ways.
Did they give any suggestion as to what the data track could be usedfor, and what the data rate was.
The BKSTS wallchart, at least the older version of it which I have, but probably the current one as well, has a frame of Comtrak, but the tracks are so narrow that it's difficult to see any detail.
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