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Topic: What is the acceptable tolerance from exactly 24 fps for motion pictures?

Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 02-01-2017 07:23 PM

Sam: By and large you are correct. Id did get better with sync motors and belts with teeth. (I measured 1440 on the shutter shaft reliably.)

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 02-01-2017 09:52 PM

Sync motors held correct speed of course, but there were a lot of V belt drives around when SR.D was designed so that had to be accounted for. Flutter tended to be higher on toothed belt Century's unless everything was perfect.

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 02-06-2017 08:23 AM

Quite a few exhibitors in europe followed a bad habit of operating their machines at 25fps in order to squeeze out a few minutes per day, and obviously, SRD and DTS was able to follow.

I once overheard a couple at an exhibitor conference complaining that this is no longer possible with DCI ;-)

- Carsten

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 02-06-2017 10:10 AM

Back in Western Electric days there was a speed control on some systems and it was used by some to speed up the shows. Not that I was there, but I heard from people who were.

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 02-06-2017 11:57 AM

quote: David Buckley
Tone-wheel Hammond organs are also locked to the mains frequency, and in normal use, folks don't complain about them going out of tune.

I once stage managed an outdoor concert where the band used a B-3.

About ten minutes into the show, people started to notice that the organ was playing out of tune.

After some investigation, I found out that the diesel generator which poweried the venue was only running at 59 Hz. Since the organ used a synchronous motor to operate the tone wheel it was playing 1.667% off-pitch.

If you assume that a piano or organ should play the note of "A" as 440 Hz. when the line freq. is 60 cycles per second then it would play an "A" at 432.667 Hz. when the line freq. is 59 cycles.

That means the organ was playing half way between an "A" and an "A-Flat."

It was definitely noticeable.

If a movie projector was playing 1.667% (59/60) of its normal speed i imagine it would be just as noticible.

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Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 02-06-2017 03:44 PM

quote: Carsten Kurz
Quite a few exhibitors in europe followed a bad habit of operating their machines at 25fps in order to squeeze out a few minutes per day

When you think about it this is pointless. Realistically they aren't saving more than 2-3 minutes per show. Over 4-5 shows a day, this isn't enough time to really change the show times or even fit in an extra show. Maybe you save 10-15 minutes by the end of the day, which means little more than the manager gets to go home a bit earlier.

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 02-06-2017 05:08 PM

Well, could sum up to 20-30 minutes per day. Those beancounters would probably find this worth the small effort.

- Carsten

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Martin McCaffery
Film God

Posts: 2481
From: Montgomery, AL
Registered: Jun 99

posted 02-06-2017 06:07 PM

I've heard it alleged (by Paul Simon among others) that radio DJ's back in the 45rpm era would do this also to make room for a little bit more advertising.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 02-07-2017 06:42 AM

Speeding up songs was a fact on radio...I stopped listening to radio for music as a result.

I knew a theatre that deliberately modified their Century poly-v pulleys to cut down on show times and likewise, I knew an operator that would run a projector fast to get out a couple of minutes earlier. As a projectionist, I've been told by the manager to start the last show early but to ensure that the feature didn't start before the published showtime just so they could get out a few minutes earlier. I condone NONE OF THIS.

BTW...I've yet to turn up an SMPTE spec that gives a tolerance to the 24fps speed. I've now kicked it up a bit to see if it actually, in fact, exists. There are numerous locations were the 24fps speed is mentioned/referenced but it is always an exact number, never with a tolerance. I would think that such a tolerance would need to be a function of the desired speed so that it scales. However, the audio portion will be much more readily noticed before people notice a picture speed variance.

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Jack Ondracek
Film God

Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002

posted 02-07-2017 09:23 AM

quote: Martin McCaffery
I've heard it alleged (by Paul Simon among others) that radio DJ's back in the 45rpm era would do this also to make room for a little bit more advertising.

This is partially true. The decision to raise the turntable speeds didn't come from the DJs, but somewhere between the program director and management levels.

It wasn't to allow for more time for commercials, as that number was set ("forcefully suggested") by government rule. Rather, it was to make the music more "exciting", and raise the station's appeal to its listeners. More listeners = more ad $$

That didn't transfer well to movies however, at least not to me.

For some 20 years or so, one of the theatres I'd eventually work for had the wrong drive belts on both of its Centurys, causing a higher speed. It wasn't until we put a platter and stereo sound in the place that I was able to get the tech to consider there might be a problem. One stupid belt and the sound became normal. They had never considered it as their single show per night didn't put enough hours on the belt to ever become a problem and... I guess, my boss might have been tone deaf.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 02-07-2017 10:09 AM

The drive system on my FR-35B was crystal controlled. That projector was designed in the mid 1980's!

Mark

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 02-07-2017 11:33 AM

FR 35 was never used in cinemas. Telecine, film chain, yes, where speed was more critical.

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Martin Brooks
Jedi Master Film Handler

Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002

posted 02-18-2017 05:49 PM

quote: Martin McCaffery
I've heard it alleged (by Paul Simon among others) that radio DJ's back in the 45rpm era would do this also to make room for a little bit more advertising.

It wasn't to make room for more advertising. It was to make the station sound more exciting by increasing the tempo. Among other stations, WPLJ 95.5 FM in NYC did this back in the 70's or 80's.

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Rex Oliver
Film Handler

Posts: 65
From: Greenville, NC. USA
Registered: Apr 2013

posted 02-19-2017 02:06 AM

The top forty station I worked for did the speed uptempo bit as well.WPGC AM/FM in Wash DC.They used EMT TT's with a speed controller homebuilt from an Op-Amp Labs variable oscillator module and a Crown DC 150 Amp feeding a step up transformer-then to to the TT motor.Later the EMT TT's were replaced by Technic SP10-then the outside variable frequency supply was no longer needed.Languised in the station junkpile at the transmitter building.The Crown Amp was 'recycled" as another monitor amp at the transmitter plant.

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Jim Cassedy
Phenomenal Film Handler

Posts: 1661
From: San Francisco, CA
Registered: Dec 2006

posted 02-19-2017 10:46 AM

quote: Justin Hamaker
I wonder how much variation from 24 fps is possible before it is noticed by the viewer.

I'm guessing that uneven speed, such as from one of those old Bell & Howell
16mm projectors with a flakey mechanical governor, would be more noticeable,
(and annoying) audio-wise, than a projector that ran a frame-or-two off speed,
but at a constant rate. I'll bet most movie goers, unless they had a really good
'ear', probably wouldn't notice if a projector's speed was off by a constant few fr/ps.

Interesting anecdote:
A couple of years ago I was doing a rehearsal with a small orchestra that
was going to be playing with a rare silent film. These guys were professional
'silent film musicians' and did this all the time.

About 10sec into the rehearsal, the stage manger was on the comm-radio
saying that the orchestra leader was asking for me to double check the
projector speed.

The speed was supposed to be 18fr/sec, but I accidentally fat-fingered
19fr/sec when I was punching numbers into the speed controller.
(or maybe it was the other way around)

But whatever... I was pretty impressed that those guys could tell I was just
one friggin' frame-per-second off speed so quickly. [thumbsup]

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