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 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Tue 05, 2017 12:51 am 

Joined: Feb Mon 06, 2012 7:24 pm
Posts: 2487
Location: Gold Country, (Stanislaus National Forest) California 95235
simplex1040 wrote:
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.
Which means the film comes in rolling continuously smooth and then the top loop has to make room for the stop and start motion for keeping each frame briefly still behind the lens - and then the bottom loop has to have an equal amount of space to reverse the process so that the sound can be read.

As Dolby Digital is located above and below inline with the sprocket holes - technically it's the only sound format that could ever be read in the film gate by having four miniature digital readers in a row - and its also the only one that could technically be read by a prism off the picture lamp even though they never did it that way.
19&41 wrote:
RCA had developed an optical film recording unit that appeared as practical as the other means of recording available.
In the case of optical sound film - it has no stop and start motion like picture film.

Here's a 16MM representation of what a 35MM Fantasound track would have looked like - except
1. it would be variable area instead of variable density -
2. the track would be negative (clear lines on a black film) and
3. the tracks would be equidistant to each other instead of two hugging one edge and two hugging the other edge and a guardband on the middle.

This one is for a ride/attraction that had 3 audio channels and a cue tone track just like Fantasound would have had.

They could have also just as easily offset the audio ahead of the picture instead of behind it in what's called a ``penthouse'' like they did for mag as well as most digital processes - except for like I said Dolby Digital which they tried to experiment with shunting light off the main lamphouse bulb while it was in the film gate - but that meant the reader had to be mounted on the lens housing and would never be able to stay in alignment long enough to be any good to anybody - not to mention the lamphouse light was hundreds of times stronger than it needed to be to pick up the DD pixels.
How about frame rates?
Standard frame rates for countries on 60Hz 110/220 power is 24 FPS (90 feet/min) which means every frame is projected twice to account for an equivalent of 48 FPS.

Higher resolution films like some of the amusement park rides are FILMED at 48 FPS and each frame is then projected once at twice the linear speed of 180 feet/min for standard 4 perf 35M film.

5 perf 70MM 6 track mag non anamorphic runs at 6/5 or 112.5 feet.min

15 perf IMAX film runs at 337.5 feet/min which is one reason they were never able to put sound on it as it would be going by the heads too fast to make a good impression

ToddAO and some amusement park films run at 30 frames/sec which is the same as TV (29.975....) which is why you see judder on videotape transfers of film because they have to take 24 FPS and turn it into 30 while leaving tha audio intact.

They do this by having a shutter blade that has 2 openings on one half and 3 openings on the other half - meaning that odd frames get the normal 2 showings a second and the even frames get 3 while the sound plays normally at 24.

In countries that have 50Hz 240 power the film rate is 25 FPS and so is the video - meaning when you watch films made on the 24 FPS system on a 25 FPS video system - there's a 4% speedup (or slowdown in the case of vice versa) which although close to imperceptible by a normal viewer will still be noticeable.

Their OWN films however will playback just fine on their own video system because the frame rates match - just like when some TV shows originally shot on film shoot at 30 frames/sec in the US to be transferred straight across to video without having to be run through a telecine.

Apart from some systems that allow for 24 FPS VIDEO playback instead of the normal video rate of 30FPS (watch a camera shoot a monitor - not a trace of flicker - meaning it's a 24 FPS camera shooting a specialty monitor rigged for 24FPS playback - or both are ganged together at 30FPS.)

Some amusement park films run as high as 60 frames/sec which you can multiply out the linear speed of the film by obtaining the number of perforations in the frame and the number of frames per sec.

Older and smaller gauge films (8MM 16MM handcranked or silent 35MM) have different frame rates. Standard 16MM sound film is the same as 35MM - 24 FPS in this half the world - 25 in the other half.

Silent 35MM could be anywhere between 12 and 20 depending - but was standardized to 18. Some 16MM sound projectors have a SILENT switch which merely changes the film speed from 24 FPS to 18 which is about like changing a speed on a turntable from 45 to 33.

The reason the sound is so crappy on 8MM and 16MM film is the low linear speed - about like the difference between linear non hi fi analog sound on a 2 hour VHS vs a 6 hour VHS. 16MM linear speed is around 6 IPS when most high fidelity music reel to reel recorders lowest speed is 7-1/2 and mastered at 15. Same for 8MM which is around 3 IPS.

8MM can be either 16 FPS or 18 although 12FPS is also standard esp for old home movies. Since these have to be either run at speed or telecined to match video - the most common scenario is to run 8MM at 15 FPS and double up the frame rate - meaning on video they'll either be a touch slow from an original frame rate of 16 or 18 or a little fast from an original frame rate of 12.

However there is magnetic as well as optical sound 8MM film some of which is also run at the standard 24 FPS with its extremely small pictures and extremely narrow magnetic or optical sound. Even at 24FPS - 8MM simply does not have the resolution to have good fidelity audio in either format or a clear picture either - with 16MM not being that much better.

But people never really bought release prints of films because of the huge amount of film it took for an average picture. Airlines where the format took off for the longest didn't care because in the early days of 2 projectors each running one reel at a time - they could keep going back and forth however many times they wanted just as the commercial cinemas did with their 20 minute reels back in the days before they perfected hour long fire carbons and electric lights.

Then later when they went to endless loop cartridges - again e g airlines didn't care how big the cart was bec all they did was slide it in the player and slide it out again so it could be 2 feet across and it was still better than trying to do the same thing in 16MM or 35.

With improvements in slow-speed magnetic films in the 80s (think the film equivalent of EE reel tape designed to give 7-1/2 fidelity at 3-3/4 - or the equivalent to a Chrome or Metal cassette) then it was a little better esp w the wider tracks on dual system (Super16 film and separate 2 track audio film) - but again nowhere near what you could get on even NORMAL 35MM dual-system film (1.33:1 aspect ratio) nevermind SUPER 35 (1.375:1 ratio) with a separate 3-track 4-track or 6-track mag film running alongside.

As this is not a film forum, if you are interested in delving deeper into the technological aspect of that medium I would recommend that you avail yourself of the resources located there and/or the History of Cinema program at your nearby junior college.

2 kinds of men/tape. Low Noise/Wide Range.
LN=kind. WR=abrasive. Engineers=same thing.

 Post subject: Re: How was analog sound on film done?
PostPosted: Dec Tue 05, 2017 2:16 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9151
Location: 42001 KY
processhead wrote:
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.

I have never used a term for that.

Film comes off the reel ( or platter) , around the upper sprocket( feed sprocket), into the upper loop then it enters the film gate and goes across the aperture and hits a sprocket called the intermitant sprocket. This sprocket is timed to the shutter to only move the film when the shutter is closed. it moves at 24 frames per sec ( sound film 16 for silent) so the intermittant pulls the film through the gate 24 times a second. after leaving the film gate the film hits the lower loop, the on to the lower sprocket and heads into the analog sound head. There are a set of tension rollers a antiwarble drum and another sprocket to pull the film through the sound head. Then the film heads to the take up reel or platter depending on system.

Film camera is same 24 frames per second with intermittant and such that the projector has.

IMAX uses a vacuum that pulls the film against the film gate in front of the lens so there is no mechanical intermittant gear.

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