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» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » What is the acceptable tolerance from exactly 24 fps for motion pictures? (Page 3)

 
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Author Topic: What is the acceptable tolerance from exactly 24 fps for motion pictures?
Steve Guttag
We forgot the crackers Gromit!!!

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


 - posted 02-19-2017 12:51 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Jim, you are so wrong. Even a 1fps variance in a 24/25fps system is quite noticeable in pitch.

In your silent film case, you are talking about over a 5% faster speed. The musicians/conductor are likely using a metronome to ensure that they stay at the right pace. 5% is HUGE to be off.

When I've done silent films, I've had situations were we were down to 2/100ths of a frame per second (depends on the movie and who is orchestrating, really).

In fact, I found that supplying a mere 2-digit readout to be insufficient for sites that were going to be doing silent movies with such accompaniment and would specify 3-digit (tenth of a frame per second readout) in order to be accurate enough. Many times, when they rehearse, they time a passage for how long it should be and where the beats are. So you may be matching another projector's inaccuracy or even a video player and all of what it took to get the image onto that device.

BL&S on some of their road show type events had dubber that only had the time code information on it and a "clock" for the conductor to gauge themselves with to ensure that the musicians were always in time with the movie.

The musicians of the day never had it so good!

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
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 - posted 02-19-2017 01:22 PM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
Our local top 40 station had Gates turntables, 3 speed. 33-45-45+. They turned down the 78 rpm position in a lathe. Two problems: Some songs sounded terrible when up-pitched. The two turntables were not exactly the same speed; I could tell them which turntable they were using.

The biggest problem that those of us with perfect pitch had was that notes moved up to the cracks where no real note existed.

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Scott Norwood
Film God

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From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 02-19-2017 01:48 PM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
When I was in high school (early '90s) some friends and I noticed that the local top-40 station (WXKS-FM) was playing many songs about 1-2% fast. I assume that they were using CDs (or maybe carts) at that point, but the change in pitch from what it should have been was unmistakable for anyone familiar with the songs that they were playing. Did normal people notice? Apparently, not enough to get them to stop doing that. No doubt, a classical station that tried something like that would be flooded with complaints.

I have no idea if they still do this. I don't normally listen to top-40 radio now.

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Randy Stankey
Film God

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From: Erie, Pennsylvania
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 - posted 02-19-2017 02:19 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
quote: Jim Cassedy
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.

Wouldn't happen to be I Musici de Montreal, per chance? Would it?

I did two gigs with them. First one was Phantom of the Opera. Second was Pictures at an Exhibition.

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David Buckley
Jedi Master Film Handler

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From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004


 - posted 02-19-2017 03:19 PM      Profile for David Buckley   Author's Homepage   Email David Buckley   Send New Private Message       Edit/Delete Post 
With computer playout being the norm on radio stations, nowadays tracks generally get played at the right tempo. Except when it's close to the top of the hour, and then the software stretches or shrinks the track to fit perfectly. Sometimes the time change involves a pitch change, sometimes it doesn't, depends on the software.

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Jim Cassedy
Phenomenal Film Handler

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


 - posted 02-19-2017 03:19 PM      Profile for Jim Cassedy   Email Jim Cassedy   Send New Private Message       Edit/Delete Post 
quote: Steve Guttag
Jim, you are so wrong.
Well Steve, I guess I was looking at the situation wrong, (like- "what's 1 little frame
fast or slow out of 24?") and making a few assumptions; but I can't argue with your
math, the percentage of speed tolerances you give would definitely be noticeable.

So, 'yes' I was wrong. (But please don't tell anyone)

quote: Randy Stankey
Wouldn't happen to be I Musici de Montreal, per chance?
Honestly, Randy- this was abt 4 years ago and I really don't recall the name
of the group or where they were from. I'm familiar with Musici de Montreal,
and I can pretty certainly say it wasn't them.

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Steve Guttag
We forgot the crackers Gromit!!!

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


 - posted 02-19-2017 07:41 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Jim...note, people won't notice the motion being off that much but when you are dealing with musicians, their livelihood partially depends on them keeping time...yes, they'll notice. The layperson will notice the pitch change, for sure. Particularly if they have any frame of reference (they know how the actor should sound or a piece of music or if everyone just sounds too high or low...you'd be amazed at at how sensitive the human ear is to pitch (just about anyone's). It is sort of like lip sync. You can get away with sound being delayed too much by a wide margin but you best never have sound lead the image, the brain KNOWS something isn't right. We're built with sound lagging image (people/objects are not at zero distance so in real life, sound always lags image, never the other way around.

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Sam D. Chavez
Film God

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From: Martinez, CA USA
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 - posted 02-19-2017 08:56 PM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
d also be a v35 mag sound reel to reel could be annoying because any splices would be heard before being seen and the effect was always jarring especially when running an old print. There coulariation in the speed when the spice hit the Davis loop rollers, also annoying.

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Jack Theakston
Master Film Handler

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From: New York, USA
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 - posted 02-20-2017 10:43 AM      Profile for Jack Theakston   Email Jack Theakston   Send New Private Message       Edit/Delete Post 
There are musicians and conductors today that basically need a click-track to conduct, but I can assure you that back in the actual silent era, no such thing was possible or necessary. The conductor had to truly be in charge of the orchestra and make tempo adjustments on the fly. Larger theaters had a call box from the orchestra pit/organ console up to the booth so that the conductor or organist could tell the projectionist to slow down or speed up.

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Sam D. Chavez
Film God

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From: Martinez, CA USA
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 - posted 02-20-2017 09:36 PM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
quote: Sam D. Chavez
d also be a v35 mag sound reel to reel could be annoying because any splices would be heard before being seen and the effect was always jarring especially when running an old print. There coulariation in the speed when the spice hit the Davis loop rollers, also annoying.
Well that was weird! I was having internet problems when posting and it got garbled. Just agreeing with Guttag that sound that leads the picture just feels wrong.

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George Lemaster
Film Handler

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From: Falls Church, Virginia
Registered: Sep 2017


 - posted 09-19-2017 10:24 PM      Profile for George Lemaster   Author's Homepage   Email George Lemaster   Send New Private Message       Edit/Delete Post 
Film shot at 24 fps was projected at 25 fps on television systems in countries using 50 Hz power, and therefore a 50 Hz field rate video (405/50 or 625/50). The resulting increase in audio pitch was accepted. USA television, 525/60, with 60 Hz power, used projectors with a "3/2" pulldown so the film speed was correct at 24 fps but compatible with a 60 Hz field rate. The earliest telecine projectors did this, such as the RCA TP16, with a synchronous 60 Hz motor, produced in 1940's. http://www.earlytelevision.org/rca_tp-16.html

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Mitchell Dvoskin
Phenomenal Film Handler

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From: West Milford, NJ, USA
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 - posted 09-20-2017 01:34 PM      Profile for Mitchell Dvoskin   Email Mitchell Dvoskin   Send New Private Message       Edit/Delete Post 
In 2011, there was a widely reported proposal to eliminate the federal regulations regarding reliable 60hz power in the USA.

Was this ever implemented?

NBC NEWS

quote: NBC NEWS/Associated Press
A yearlong experiment with America's electric grid could mess up traffic lights, security systems and some computers — and make plug-in clocks and appliances like programmable coffeemakers run up to 20 minutes fast.

"A lot of people are going to have things break and they're not going to know why," said Demetrios Matsakis, head of the time service department at the U.S. Naval Observatory, one of two official timekeeping agencies in the federal government.

Since 1930, electric clocks have kept time based on the rate of the electrical current that powers them. If the current slips off its usual rate, clocks run a little fast or slow. Power companies now take steps to correct it and keep the frequency of the current — and the time — as precise as possible.

The group that oversees the U.S. power grid is proposing an experiment that would allow more frequency variation than it does now without corrections, according to a company presentation obtained by The Associated Press.

Officials say they want to try this to make the power supply more reliable, save money and reduce what may be needless efforts. The test is tentatively set to start in mid-July, but that could change.

Tweaking the power grid's frequency is expensive and takes a lot of effort, said Joe McClelland, head of electric reliability for the Federal Energy Regulatory Commission.

"Is anyone using the grid to keep track of time?" McClelland said. "Let's see if anyone complains if we eliminate it."

Won't affect GPS or Internet
No one is quite sure what will be affected. This won't change the clocks in cellphones, GPS or even on computers, and it won't have anything to do with official U.S. time or Internet time.

But wall clocks and those on ovens and coffeemakers — anything that flashes "12:00" when it loses power — may be just a bit off every second, and that error can grow with time.

It's not easy figuring what will run fast and what won't. For example, VCRs or DVRs that get their time from cable systems or the Internet probably won't be affected, but those with clocks tied to the electric current will be off a bit, Matsakis said.

This will be an interesting experiment to see how dependent our timekeeping is on the power grid, Matsakis said.

The North American Electric Reliability Corp. runs the nation's interlocking web of transmission lines and power plants. A June 14 company presentation spelled out the potential effects of the change: East Coast clocks may run as much as 20 minutes fast over a year, but West Coast clocks are only likely to be off by 8 minutes. In Texas, it's only an expected speedup of 2 minutes.

Some parts of the grid, like in the East, tend to run faster than others. Errors add up. If the grid averages just over 60 cycles a second, clocks that rely on the grid will gain 14 seconds per day, according to the company's presentation.

Spokeswoman Kimberly Mielcarek said the company is still discussing the test and gauging reactions to its proposal, and may delay the experiment a bit.

Aimed at making grid more reliable
Mielcarek said in an email that the change is about making the grid more reliable and that correcting the frequency for time deviations can cause other unnecessary problems for the grid. She wrote that any problems from the test are only possibilities.

In the future, more use of renewable energy from the sun and wind will mean more variations in frequency on the grid, McClelland said. Solar and wind power can drop off the grid with momentary changes in weather. Correcting those deviations is expensive and requires instant backup power to be always at the ready, he said.

The test makes sense and should not cause too much of a hassle for people, said Jay Apt, a business professor and director of the Electricity Industry Center at Carnegie Mellon University.

But Tom O'Brian, who heads the time and frequency division at the National Institute of Standards and Technology, expects widespread effects.

He said there are alternatives if people have problems from the test: The federal government provides the official time by telephone and on the Internet.


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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
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 - posted 09-20-2017 03:32 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Sam D. Chavez
There were plenty of slow running Century with aluminum drive pulleys. I measured one at 21FPS.
Sheesh! Is this movie ever going to end???

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George Lemaster
Film Handler

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From: Falls Church, Virginia
Registered: Sep 2017


 - posted 09-20-2017 03:48 PM      Profile for George Lemaster   Author's Homepage   Email George Lemaster   Send New Private Message       Edit/Delete Post 
There are three networked power grids in continental USA, East, West, and Texas. Within each network the frequency tolerance is extremely tight, as you can envision hundreds of power station generators operating in parallel so they are essentially locked together. Also, typical steam turbines must operate very close, tenths of a HZ to 60, or it can quickly sustain extremely expensive damage to the turbine blades. A couple of hundredths of a Hz is typical USA tolerance for this complex network issue: http://www.nerc.com/docs/oc/rs/NERC%20Balancing%20and%20Frequency%20Control%20040520111.pdf

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Rick Raskin
Phenomenal Film Handler

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From: Manassas Virginia
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 - posted 09-20-2017 04:42 PM      Profile for Rick Raskin   Email Rick Raskin   Send New Private Message       Edit/Delete Post 
quote:
Won't affect GPS or Internet
No one is quite sure what will be affected. This won't change the clocks in cellphones, GPS or even on computers, and it won't have anything to do with official U.S. time or Internet time.

Correct. That's because terrestrial network timing is derived from a Stratum 1 source, usually GPS or Cesium clock.

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