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 Post subject: How was analog sound on film done?
PostPosted: Dec Sat 02, 2017 9:23 pm 
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I think I understand the concept, a light shines through the film and activates a photocell. How does light create sound though? I must be missing something.


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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sat 02, 2017 9:43 pm 
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There was a special area along the side of the film.

The audio was recorded there as a transparent area of varying width.
The width corresponded to the instantaneous amplitude of the sound.

Special gearing in the projector changed the film motion from stepping to smooth.
That resulted in a smooth sound track.,

That was read by a photocell and sent on to the amplifier.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sat 02, 2017 9:55 pm 
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It could be variable width, or variable density of the sound track on the film. Light shining on one side of the track is modulated by the track and then hits a photocell where it is amplified. The photocell is a variable resistor who's resistance is depending on the amount of light hitting it.


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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sat 02, 2017 10:52 pm 
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nice Q&A, often wondered that myself, thanks guys.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sat 02, 2017 11:32 pm 
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The gearing actually was the other way around. it was all all smooth running except right at the lens where there is an intemittant gear that does the stepping in front of the lens(the reason for the upper and lower film loop in the path, these had to be synced with the shutter or you got "travel ghosts" on the screen.

in the sound head the film runs over a anti warble drum that is a big flywheel.

Back in the late 90's they changed the film stock to a cyan dye base and the analog readers did not read as well with an incandescent light source. Red LED lamps could be retro fitted on a projectors.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 12:37 am 
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I know they used disc recording until the late 1940’s/early 50’s for audio recordings of bands, why didn’t they use film to record? I ask that as a person that knows nothing about it. (Obviously)


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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 12:57 am 
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Joseph Newton wrote:
I know they used disc recording until the late 1940’s/early 50’s for audio recordings of bands, why didn’t they use film to record? I ask that as a person that knows nothing about it. (Obviously)


Cost and fidelity.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 12:57 am 
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Joseph Newton wrote:
I know they used disc recording until the late 1940’s/early 50’s for audio recordings of bands, why didn’t they use film to record? I ask that as a person that knows nothing about it. (Obviously)


Cost might be one reason, also frequency response, possibly. (Beat me to it.)
The older projectors used a phototube, usually a gas one. 1P40 and 921 come to mind.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 1:23 am 
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Well in the 50s and 60s they did use 35 MM magnetic tape made like movie film for some music recording. Several companies used that technique for awhile but it was costly and harder than just a plain old Ampex recorder. But records made with the 35MM magnetic film have an astounding realism and dynamic sound. About like digital or better. Better signal to noise, dynamic range, distortion and wow and flutter using the film handling type mechanisms. Back in the late 20s and early 30s they actually did movie soundtracks on big discs. Had a disc player right on the projector. Guess that getting them in synch might have been a challenge.


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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 2:16 am 
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wazz wrote:
Well in the 50s and 60s they did use 35 MM magnetic tape made like movie film for some music recording. Several companies used that technique for awhile but it was costly and harder than just a plain old Ampex recorder. But records made with the 35MM magnetic film have an astounding realism and dynamic sound. About like digital or better. Better signal to noise, dynamic range, distortion and wow and flutter using the film handling type mechanisms. Back in the late 20s and early 30s they actually did movie soundtracks on big discs. Had a disc player right on the projector. Guess that getting them in synch might have been a challenge.



Vitaphone was the disc system Played from inside out. Sound on film came soon after and disc systems went away quickly .

Most 35mm magnetics were used in the film editing and final mixing phases before the final print.

optical sound was easier at the movie theatre level. Both RCA and Western Electric sound would play on the same equipment.

When digital sound came out in the 90's one version went back to disc, time code was on the film and sound was on CD.
DTS system. in my opinion sounded much better than Dolby Digital or Sony Digital (SDDS) which had the "sound files" on the film. Sony was on the outside of the perfs ( on both sides) and Dolby was between the Perfs on the optical sound side.
Sony and Dolby were bad to jump out of digital due to damage on the print. DTS could keep playing and find the time code back without jumping out of digital.

IMAX 70mm had no sound on the film, It was synced with multitrack 35mm magnetic playback using a timecode reader.
IMAX was also shot and played horizontal on the film rather than vertical so the film went through side to side rather than top to bottom. It used a 7K watt lamp.

Most of my auditoriums used 2-3k watt lamps I had 4 that used 7K ( not IMAX just big screens)

today a move theater projector is nothing more than a linux based media player that has hardware that will decode the DCP (digital cinema packages). instead of the software decoding, it is built into the firmware of the projector. this also allows for encryption of the file. You have to have a KDM decrypt key to play the movie and most are tailored to your specific projector. the KDM expire and you can no longer play the movie after your engagement ends ( you copy the movie to your server to play it. )

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 3:28 am 
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wazz wrote:
Well in the 50s and 60s they did use 35 MM magnetic tape made like movie film for some music recording. Several companies used that technique for awhile but it was costly and harder than just a plain old Ampex recorder. But records made with the 35MM magnetic film have an astounding realism and dynamic sound. About like digital or better. Better signal to noise, dynamic range, distortion and wow and flutter using the film handling type mechanisms. Back in the late 20s and early 30s they actually did movie soundtracks on big discs. Had a disc player right on the projector. Guess that getting them in synch might have been a challenge.


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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 10:40 am 
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The also powered the sound exciter light with high frequency AC. I seem to remember
it used a 6V6.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 2:24 pm 
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That circuit was mostly used on small 16mm projectors. Theatre equipment used motor-generator sets in the early days, or high-current D.C. supplies using Tungar tube rectifiers. Some of those were huge; one RCA model weighed 100 pounds! Many of those were converted to use silicon diodes later.

Another scheme was to use AC on the exciter lamp filaments, with bulbs having large filaments which had more thermal mass, to keep the hum out of the audio. This was often done in drive-in theatre sound systems, where the low-frequency response was restricted by the small speakers used, and sometimes rolled off in the preamp or volume control circuits as well.

In later years, engineers realized that the exciter lamps could be turned off and on when changeovers were made, instead of having both of them lit at the same time; this cut the current requirement for the power supply in half. With silicon diodes, the exciter supply could then be much smaller and lighter.

For optical pickup, most systems used 868 or 918 phototubes. Western Electric systems used their own tubes, of course.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 9:47 pm 
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wazz wrote:
Guess that getting the disc and film in synch might have been a challenge.
Sound on Disc was perfect. https://www.youtube.com/watch?v=-j8GwkniGrU
No! No! No! Yes! Yes! Yes! (slide over to 3:00) https://www.youtube.com/watch?v=P6CuBK0cgX4
Fantasia Liner Notes wrote:
In 1939, when the music for this motion picture was recorded, optical photographic film, even with its' inherent high noise level and other limitations, was the only suitable recording medium. The results were considered sensational and seldom, if ever, has the marriage between picture and sound been so complete.
In 1955 the handful of remaining Fantasound audio prints were collected and assembled in the basement of the Walt Disney Studios in Burbank and sent over Class A telephone lines to what at that time remained of what was originally called RCA Photophone who had developed the system in the first place and recorded onto 3-track full coat 35MM film. This is the music master we hear today - a transfer off that first-generation magnetic master.

On the other hand - Magnetic/Optical prints of the mid `50s that were made for theatres that hadn't yet adopted 4-track magnetic stereo sound - either had 4-track mag striped onto the film for stereo and a half-width unilateral monaural track squeezed inbetween or else a monaural mag stripe on one edge with a balance stripe on the other so it wouldn't fall off the spool from being lopsided - and then the standard width optical track in its' normal place.

In the case of stereo and surround optical tracks - it sort of resembles an inverse version of a bilateral mono variable area track. These can either be positive (two black stripes running down the middle of an otherwise clear area) or negative (two clear lines running down the middle of an otherwise black area).

Debates abound as to which is the quieter track - with the pro-neg people saying that their track acts like a noise gate while the pro-pos people say their track occupies so much of the available area that you don't need it.

Sound on film was originally produced with the same silver nitrate as any black and white film. In fact this is how you can tell an original IB Technicolor dye transfer print (which won't fade) from a later restrike 9which will turn red or brown or....). The IBT print will have what appears to be a black-and-white soundtrack

Later tracks used one or more dye configurations - some of which have trouble being read by a standard incandescent exciter lamp, necessitating a changeover to a red LED equivalent.

There are people that say the opposite color LED to the dye in the track (red LEDs to a cyan track and blue LEDs to a High-Magenta track) gives the best performance - but engineers are still out on that one.

In the case of stereo or surround - a regular stereo optical track is just a dual-bilateral with different programming on each half. When played over a matrix-based surround system (Dolby Stereo, Ultra Stereo etc) SOME rear information will be there naturally in the form of ambience and other sounds.

Nothing will be there on purpose however - it's all accidental as the matrix will pick up any phase differential between the two tracks (L-R) and send it to the monaural surrounds while it takes any common information (C) and sends that to the center channel behind the screen whether it was placed there on purpose or not.

For surround-encoded films, derivations of the original Sansui QS quadraphonic matrix developed for LPs in the 70s is used (Left Center Right and Monaural Surround). For split-surround - a second matrix is added to the first - L-C and R-C and (very simply) those are encoded with 90-degree phase differences to the main channels and mixed in accordingly.

This is so that a 5.1 dual bilateral stereo variable area track will stilll play properly on a 4.0 system with mono surrounds as 90 and 90 = 180 which is what Dolby 4.0 uses.

More here: http://www.lothiansradiosociety.com/mee ... son-gm3psp
simplex1040 wrote:
IMAX 70mm had no sound on the film.
It was synched with multitrack 35mm magnetic playback using a timecode reader.
Until digital came out after which it synched to the same types of external optical-disc based systems as DTS - which is how it still is today for the few cinemas that do analog film and digital sound. The rest have both on a series of hard drives or secure FTP links which are downloaded to the projector in question the same as regular digital cinema.
simplex1040 wrote:
IMAX was also shot and played horizontal on the film rather than vertical so the film went through side to side rather than top to bottom.
just like Paramount's VistaVision and a couple of Cinerama formats that never caught on.

Bob Leonard of Universal invented a 70MM full-coat audio film that also ran sideways. Originally developed to try and marry all the different 3-track and 4-track 35MM full coat mag formats into one film, it featured either 12 or 18 across the middle and one each between the perfs and the edge.

Only two short subjects - both considered demonstration films - were ever made in the format - one in 1953 and one in 1954 before the format was abandoned. By 1955 with all these millions of feet of 70MM full coat leftover from the project and only one studio able to record onto it, a couple of avant-garde record labels tried to have a go making super-audiophile releases for 2-track inline or staggered 7-1/2 IPS consumer tape (for $18.95 a reel when the average working man's wages might only be $50 or $60 a week and a good used car could be had for a few hundred).

A handful of hundred or so of these titles that were recorded have been re-released on CD - but the transfers were taken from the 15 IPS 2-track mixdowns or the 4-track 35MM magnetic premix film masters that were run alongside the 70MM full coat as a safeguard.

Once 70MM 6-track picture film started to get traction, pretty much the rest of the original 70MM mag stock ended up being used as 1:1 print masters to check for quality before being dubbed onto the print.

In the 70MM film restoration world - a lot of times when the original sound master is deteriorated or destroyed and the session masters are lost or there's not enough intact 70MM show prints to assemble a decent quality master from which to strike a digital sound master - occasionally one of these mint condition hardly ever played 70MM full coat audition masters will be unearthed with only the tracks used in 70MM striped film and the whole middle blank between the holes and be in good enough shape to use as the sound master.

As far as disc - some of the first audiotape sessions were run at the big labels as early as 1948 - just in time for the release of the LP - but for the first few years anyway - they all had 17-1/4 inch lacquer blanks run alongside as a safety.

Most early LPs were dubbed from the lacquers and it wasn't until the 50th anniversary of the LP (way into the CD era) that a lot of these early magnetic masters were unearthed, transferred to digital and released.

But as previously reported - full-coat 35MM multitrack for records didn't really start until 1953 with a small handful of film-for-record sessions taking place in 1952 when stereo disc for LP was over five years out from being perfected. Even consumer 2-track STAGGERED decks didn't come out until late 1954 with their inline counterparts being introduced six months later when head technology had improved enough to do it on a mass scale.

Still - those early 2-track decks cost the equivalent of a year's salary - like the RCA color TVs that had come out the same year.

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Last edited by ndiamone on Dec Mon 04, 2017 4:52 am, edited 6 times in total.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Sun 03, 2017 10:32 pm 
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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Mon 04, 2017 2:02 pm 
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Can someone please elaborate on the purpose of staggering the projector drive?

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Mon 04, 2017 3:07 pm 
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processhead wrote:
Can someone please elaborate on the purpose of staggering the projector drive?


can you explain what you mean by staggering.

If you mean why does the film have loops above and after the lens it is so that the film can be stopped in front of the aperture to display the frame on the screen.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Mon 04, 2017 10:30 pm 
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During the Roosevelt administration, there was a need for audio recordings for a record of various meetings and conferences and RCA had developed an optical film recording unit that appeared as practical as the other means of recording available. There was one installed at the white house. Here is a little bit about it.

http://www.paperlessarchives.com/fdr_tapes.html

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Mon 04, 2017 10:48 pm 
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Double post.

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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Tue 05, 2017 12:41 am 
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simplex1040 wrote:
processhead wrote:
Can someone please elaborate on the purpose of staggering the projector drive?


can you explain what you mean by staggering.

If you mean why does the film have loops above and after the lens it is so that the film can be stopped in front of the aperture to display the frame on the screen.


Yeah, poor choice of words. :roll: Staggering is what I do after too many adult beverages.

What is the correct term, and how long is the frame held till advancing to the next one? Just curious about the timing sequence behind the film projection process. Imagine it has to be compatible with the original filming process.

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