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Topic: GS 1200 synch unit

Mike Peckham
Phenomenal Film Handler

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posted February 19, 2004 11:43 AM

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Hello Chaps
There's an interesting thread running on the 8mm film shooting forum at the moment about developments on a synch unit for the GS 1200 ; http://www.8mm.filmshooting.com/scripts/forum/viewtopic.php?t=4719

Kev, your new web site even gets a mention!

Mike.

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John Clancy
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posted February 20, 2004 02:21 AM

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Wow, this chap's discovered what was first invented about 25 years ago.

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Kevin Faulkner
Film God

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posted February 20, 2004 06:34 AM

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Hi guys, Now you know! the unit I have is the 1008 built by Pedro himself for me and as I said to you both before its superb and crystal locks the GS spot on. No need to have any form of video pulse going anywhere near this box as it's as rock solid as the video pulse itself. [Smile]

[Smile]

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Mike Peckham
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posted February 20, 2004 11:25 AM

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Hello John

I always thought that the unit you refer to relied on a physical connection between the video [DVD] and the GS 1200. Using the GS as a 'slave' and the Video as the 'driver'.

I think Pedros unit actually crystal locks the speed of the GS so that it will run at 25fps and keep synch with a DVD or Video which are automatically locked at that speed in Europe due to our mains operating at 50cps. I might be wrong, perhaps Kev' can explain further?

Mike

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John Clancy
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posted February 23, 2004 07:26 AM

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I only read the post quickly but if I remember he was also talking about using the ESS port for pulse on the GS. Without some sort of pulse there is no getting around the fact that there are going to be speed variations when transferring a film to video.

For example, the original laser vision disc for Star Wars is running about 26fps by the time it finishes. It was gradually just sped up on side 2 as there wasn't enough space to fit the entire film in. The Elmo is running virtually flat out keeping up with the speed increase. Now I have no idea how something locking the speed of a projector to a definite speed will deal with something like that.

Also, I've made the mistake in the past of pulsing the GS from the laser disc when I should have been synchronizing to a DVD. The result was the sound drifting out pretty quickly. After a while it was obvious there was a problem and in switching off the laser disc this shut down the motor on the GS. Just had the wrong lead into the pulse box. Plugged the video lead from the DVD into the pulse box and perfect sync' was the result.

I'm not saying a crystal sync' won't work. After all, Kevin has told us it does work. I'm obviously just missing something in how it deals with all the speed variations from every video transfer.

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Mike Peckham
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posted February 23, 2004 12:03 PM

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Kev?

[Smile]

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Ricky Daniels
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posted February 23, 2004 02:56 PM

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Hi Guys,

FYI

The video sync pulse unit referred to drives the GS at the video frame rate fed to it via the GS Interface Unit. Understand that the film to video transfer frame rate DOES NOT alter the video frame rate of the video machine you are playing back from, be it VHS, DVD, Laser Disc, etc. The video frame rate remains constant for the video system you are using be it 625/50 (pal) or 525/60 (ntsc) or whatever you have and the frame rate of the Telecine machine used to transfer the film to video does not alter this fact.

An increase in the telecine speed will mean that digitised film image data sent to the telecine digital frame store will be 'read out' at different rates (interpollated upto the output video standard if running slower than it and reduced if running faster).

The video sync unit referred to takes the composite video signal and passes it through a 'high pass filter' to remove the high frequency video picture and a 'low pass filter' to remove the LINE SYNC PULSES. What you are left with is the FIELD SYNC PULSES at the frame rate of your video system and these are sent to a GS Interface unit, then onto the GS.

A crystal sync unit is made by Daniel Werner for 25fps users see this link...

http://www.wittner-kinotechnik.de/katalog/07_vorfu/quartz.php

Good luck syncas [Cool]

[Cool]

Rick.

Ps.

Forgot to mention that 24fps film is transferred at a frame rate of 25fps for 625/50 video to fit into the 50 cycles per second electrical system (2x25=50) good for the Video Sync Unit users in areas with 50cycle supplies. However 24fps film is transferred at a 24fps fame rate for 525/60 video and interpollated up to 30 fps to fit into a 60cycle power supply. This gives 60 pulses per second (2x30) to the video sync unit mentioned above which will in turn drive a GS in 60 cycle areas with 30fps (not good for synching to 24fps film!).

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Kevin Faulkner
Film God

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posted February 24, 2004 04:34 PM

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In answer to John's question above lets see how the ESS system on the GS works. I shall be putting this on my site eventually but here goes on here.

On the drive shaft of the GS is a magnet and next to that a reed switch. This gives one pulse per frame. In normal use the spped control circuit knows there should be 18 or 24 pulses per second from the reed switch and the motor control board will keep it to these figures as acurately as possible.
Now if you feed the projector with an external pulse from say tape etc the system once agin knows that for every pulse which enters the ESS system there has to be one pulse to match it from the reed switch and this is how the ESS system works and controls the projector from an external source.
Now if you feed in a very acurate Crystal controlled pulse the machine makes sure that the two pulses are matched and voila you have a machine running spot on whatever speed the crystal is locked to. This working like as a comparator circuit and up to a point even takes in to account wear or a slack drive belt etc. Obviously if things are bad on the GS then it can all fail horrbily.
Now going to your TV source. Our TV systems be it Pal or NTSC are very precisely locked to our mains frequency. In the UK this is 50 cycles and that equates to 25 fps. The pulses in our TV system are very acurately produced because if they werent then we would see problems of picture rolling, loss of colour etc etc. From this brief description I hope you can therefore see that If you have a DVD and the same film with the same cut on super 8, it is possible to start them off at the same point and then leave them to run in perfect sync with your crystal unit controling the projector again at a rate of 25FPS.
This is eactly how the unit made by Pedro in Germany works and it has worked time after time for me. I showed the first 600 ft to Mike, Tony and Chris Q of "Flash Gordon" recorded this way and I'm sure they will tell you that the sync didnt budge an inch so to speak.
It's a good unit and simple to use its also very acurate. I actually use my unit for setting up the speed control circuits in the GS1200 as they are not allways spot on.
What I like about it is that it plugs straight into the GS ESS socket and doesnt have to run through any other unit first. That is the only conection required and doesnt need any wave shaping or filtering circuitry which would be required if the sync was taken from the video signal.
The box I have also has a stop start switch built in so that you can have the first frame of the film loaded in the GS1200's gate with the machine in record mode etc. You then start the DVD or VHS tape a little earlier than the point on the film and when the DVD reaches that point you hit the start switch and off goes the GS in hopefully perfect sync. I say hopefully because that depends on how acurately you hit the start button but then thats the case with any system.
Hope this has helped explain the setup and amde it clearer as to the operation and why it works so well.

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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John Clancy
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posted February 25, 2004 02:21 AM

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So how does it work when a film is transferred to video at variable speed?

The points I made before were:-

1) Star Wars laser vision disc from 1982 is gradually sped up on side 2 as there wasn't enough space on the disc. If the projector is locked to 25fps it is not going to keep up.

2) If all films are transferred to video at the same 25fps rate why, when using sync' pulse, does one film driving the projector not drive it at the same speed as another? The example I gave was when I mistakenly had the laser disc driving the projector when I should have been using the DVD.

Very intriguing. Also, I rarely use sync' pulse for recording prints. It's much more often used just for enjoying the best sound available on disc with the best picture available on film.

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Ricky Daniels
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posted February 25, 2004 07:53 AM

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Hi John,

At the risk of teaching ones Grandmother to suck eggs as stated the Video Sync Unit will drive the GS at the frame rate of the video system fed to it, in 625/50 (Pal) that'll be 25fps, this will remain constant.

So a Video/DVD/Laser Disc copy of a movie filmed at 24fps and transferred to video at 25fps (as is usual in the UK) and used as the input to the Video Sync Unit/GS Interface, will drive a GS loaded with a Super 8mm reduction print of the same movie shot at 24fps, at a constant 25fps. Sync will be maintained provided the 'cut' of the Super 8 print is identical to that of the transferred print = ONE HAPPY SHOWMAN! [Big Grin]

[Big Grin]

Now if the Video/DVD/Laser Disc material does not have an original transfer speed of 25fps (or is from a converted 525/60 master or was not transferred at a constant speed!) the GS will happily continue along at the video frame rate fed to it and will not chase the original telecine transfer speed(s) = ONE UNHAPPY SHOWMAN! [Frown]

[Frown]

Understand that the GS is just getting modified FRAME SYNC PULSES from the video system of the video media you are playing back and not from the input material recorded onto that media.

ATB. Rick.

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Mike Peckham
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posted February 25, 2004 11:52 AM

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Hello everyone

For what it's worth I can certainly testify that Kevs' copy of Flash re-recorded from video is in absolutely perfect synch from begining to end and is also a fine 'full bodied' stereo recording.

Like the other guys at the 'Lightwater Mini Cine Fest' I was very impressed with what I saw and heard to the extent that having previously been a bit of a doubting Thomas about all this re-recording/synch thing I am now looking at getting into it myself. [Smile]

[Smile]

John I also heard glowing reports from Tony and Chris about your synch set-up so am hoping to have a look at that myself sometime, perhaps at a 'Russell Square' mini cine fest? [Wink]

[Wink]

Mike.

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John Whittle
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posted February 25, 2004 01:44 PM

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In short, if the film is transfered via any "variable speed" method, this synch method won't work. In the UK as you pointed out you have the luxury of a 25fps video system and the ability to speed up your film projector to 25fps for a transfer.

However, it pitch correction has been done on your video source, when you play back your film copy at 24 fps, it will sound slow. It will be in synch, but the pitch will be off by 4 per cent.

In the US, we have film at 24 fps, black and white television (any that exists) at 30 fps and color television at 29.97 fps. We get into lots of complicated math and part of the color frequency errors gives us drop frame and non-drop frame time codes for video editing.

In short, when a film is transfered via a variable speed means, either extra fields are added by the frame store to slow it down or are removed to speed it up. The machines have complicated calculations to make this less noticeable but once you've seen it happen, it becomes most distracting.

In profession sound dubbing of motion pictures, when we go back on a stage to make a correction or update, we play the stems (the original elements) against the master recording and then "phase" it in getting it not just to frame rate but to where the sound is beat for beat the same to allow re-recording or the new insert.

John

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John Clancy
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posted February 26, 2004 03:50 AM

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Ricky, I don't think I was questioning how sync' pulse works as I already have two sync' pulse setups at different locations and they work 100% until or unless the GS decides to throw a wobbly or the pulse signal is lost. It is the Crystal box I would like to understand and I think I'm going to have to see it functioning to comprehend exactly how Crystal copes with the variations in speed of video transfer.

For what it's worth Keith and I are planning a syncy pulsy fest at the May 15th BFCC. Currently we're looking at the 400 footers of Gladiator and Fifth Element through the THX sound system (but we're not finalized yet). Of course Chris, Tony and Agnello have all seen this demonstrated on a substantially smaller 10ft screen but it should be even more impactive at mind bending volume with the THX subwoofer shaking the big Victoria Hall on the 24ft screen. I know I'm looking forward to it.

Mike, any time you're up for it I'll arrange to be in. And that goes for anyone on the forum who wants to get in touch. We could always have a mass days leave from work and get together. A trip to Mr. Wilton at Ealing could also be arranged some time. He'd love to have the chance to meet everyone rather than just when it's stressful at the conventions.

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Ricky Daniels
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posted February 26, 2004 11:48 AM

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John,

I would imagine the Crystal Unit couldn't cope with variations in sync either as it appears to supply a constant pulse as Kevin states just like the video pulse unit. But it does look like it takes the hassle out of linking the video player to the GS, I may have to get one of these things too!! [Cool]

[Cool]

Good luck and please give Keith my regards, Ricky.

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Pedro Santos
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posted February 26, 2004 06:29 PM

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Hello! I am the one who put the Elmo sync unit into live.

General information:
The Elmo sync device is available in 3 variations:
1. P1008GS-Q
2. P1008GS-P
3. P1008GS-U

The first one is "only" a very accurate crystal controlled time base for the Elmo projector, driving it at exactly 16 2/3, 18, 24 or 25 fps.
Any actual video system in PAL countries runs at crystal exact 25 fps. So if you play in parallel a S8 film on a crystal controlled Elmo and on any video device, it will match. Of course, special tricky film conversions running at 26 fps or other exotic framerates won´t match! But any standard PAL edition will match without any problems.

The second is a double system sound unit, which feeds the Elmo projector with an external sync source (1000 Hz camera tape or perfo/fullcoat tape), such as recorded with my R1008MD camera interface. With this unit it is possible to create lip sync magnetic sound films with the ease of K40-S cardriges.

The third is a combination of the both. You can either crystal control the projector or sync it with external sources. While crystal controlling it, the unit can be triggerd by initial sync beeps recorded on the audio track. This way, the projector starts automatically with the first audio signal that comes.

The main purpose of these units is not only to dub sound of DVD and video to feature film prints. They are mostly designed to bridge from film projection to NLE editing. Basicaly, you can shoot your edited film with a video cam, edit your sound track on computer and transfer the ready soundtrack back to the film.

Another very useful device is the R1008MD. This unit connects to the PC contact of the film camera (flash sync contact) and outputs one 1000 Hz beep each frame the camera is shooting. This beeps are recorded to the microfone input of any sound recording device (cassette tape, MD, computer.....) The unit uses the left stereo chanel to record this sync track, while the microfone records dialogs directly to the right stereo track. No adapter cables are neccessary, as the unit connects directly to the audio recorder, using a mini stereo jack and provides another mini jack to plug in the microfone.

I know that this is a technology of the end 1960ies and 1970ies but it still works! This technology had been blown away by the Kodak sound cardrige. Now, where there is no sound film anymore, it is the only possiblilty to shoot sound film without too much effort. I did not re-invent it, I only remembered it and put it into an actual and practical design, made of nowadays components.

The complete sync system is not limited to Elmo GS1200MO.
There are other (more expensive) syncronizer units available, that fit directly for Braun Visacustic projectors and Bauer studio class projectors and can be adapted to many other projectors with DC motors.
This units are the P1008 (without crystal) and the P1008Q (4 crystals).
Both units allow external sync from tape, perfo tape and fullcoat, the Q model internal sync with crystal time base. They offer sync output for external devices like digital frame counters and has a digital universal output that can be used to sync perfo tape decks and motorized film viewers.

Pedro

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Pedro Santos
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posted February 26, 2004 06:29 PM

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Hello! I am the one who put the Elmo sync unit into live.

General information:
The Elmo sync device is available in 3 variations:
1. P1008GS-Q
2. P1008GS-P
3. P1008GS-U

The first one is "only" a very accurate crystal controlled time base for the Elmo projector, driving it at exactly 16 2/3, 18, 24 or 25 fps.
Any actual video system in PAL countries runs at crystal exact 25 fps. So if you play in parallel a S8 film on a crystal controlled Elmo and on any video device, it will match. Of course, special tricky film conversions running at 26 fps or other exotic framerates won´t match! But any standard PAL edition will match without any problems.

The second is a double system sound unit, which feeds the Elmo projector with an external sync source (1000 Hz camera tape or perfo/fullcoat tape), such as recorded with my R1008MD camera interface. With this unit it is possible to create lip sync magnetic sound films with the ease of K40-S cardriges.

The third is a combination of the both. You can either crystal control the projector or sync it with external sources. While crystal controlling it, the unit can be triggerd by initial sync beeps recorded on the audio track. This way, the projector starts automatically with the first audio signal that comes.

The main purpose of these units is not only to dub sound of DVD and video to feature film prints. They are mostly designed to bridge from film projection to NLE editing. Basicaly, you can shoot your edited film with a video cam, edit your sound track on computer and transfer the ready soundtrack back to the film.

Another very useful device is the R1008MD. This unit connects to the PC contact of the film camera (flash sync contact) and outputs one 1000 Hz beep each frame the camera is shooting. This beeps are recorded to the microfone input of any sound recording device (cassette tape, MD, computer.....) The unit uses the left stereo chanel to record this sync track, while the microfone records dialogs directly to the right stereo track. No adapter cables are neccessary, as the unit connects directly to the audio recorder, using a mini stereo jack and provides another mini jack to plug in the microfone.

I know that this is a technology of the end 1960ies and 1970ies but it still works! This technology had been blown away by the Kodak sound cardrige. Now, where there is no sound film anymore, it is the only possiblilty to shoot sound film without too much effort. I did not re-invent it, I only remembered it and put it into an actual and practical design, made of nowadays components.

The complete sync system is not limited to Elmo GS1200MO.
There are other (more expensive) syncronizer units available, that fit directly for Braun Visacustic projectors and Bauer studio class projectors and can be adapted to many other projectors with DC motors.
This units are the P1008 (without crystal) and the P1008Q (4 crystals).
Both units allow external sync from tape, perfo tape and fullcoat, the Q model internal sync with crystal time base. They offer sync output for external devices like digital frame counters and has a digital universal output that can be used to sync perfo tape decks and motorized film viewers.

Pedro

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Kevin Faulkner
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posted February 27, 2004 04:17 AM

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Hi Pedro, As I said in another thread welcome to the forum.
John lets get something cleared up hopefully at this stage about the laserdisc system. As you are aware the system can run at various speeds and I think this is where the understanding of the Laserdisc system needs to be looked at. Disc are mastered in two formats one for playing normally and one for trick play. The point about the laser disc system is that when the machines are are used in any other way toher than straight forward playing of discs they insert their own sync pulse. The sync pulse coming out of the player should allways be at 25FPS for the UK PAL system. I cant believe that you have 26FPS on some discs as otherwise some TV's especially in the eara when the LD system was developed would not lock to the pulse and would cause all sorts of problems. I have several manuals issued by Philips which describe how the LD system works and it certainly describes the whole business of sync pulse insertion when in trick play mode etc.
I'm surprised that your GS speeds up on some discs. I think John that for most us we will be using DVD and this does give a constant 25FPS and again the DVD players insert the required sync pulses if they are put into the various speed searches but also they actually move from frame to frame I think inmultiples of 25 fps rates.
My godness this is getting too complicated to put into words. I have never tried using Pedros unit with LD but it certainly works very well with VHS Hi Fi tapes and DVD's.
[Smile]

[Smile]

Kev.

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Tony Milman
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posted February 27, 2004 07:16 AM

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Guys

My Head Hurts........ [Frown]

[Frown]

How do you know all this stuff? I haven't a clue what you are talking about! Just glad you chaps do!

Me, well I am more your plug this in here, that in there, press this and off we go......

But hey, its fun reading the postings. Keep it coming

Tony [Smile]

[Smile]

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Tony

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Chris Quinn
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posted February 27, 2004 09:24 AM

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Right.
After a lot of words over the subject of pulse sync I can now tell you without a shadow of a doubt that DVD and VHS video will run locked at 25fps. How do I know this? A simple experiment that I did today, one film on DVD Life Of Brian and the other on VHS, Life of Brian, the VHS machine is ten years old and the DVD player 3 Years old.
I played the DVD and VHS in sync together and what do you know, they both stayed in sync throughout the film. I think that this now proves that what Kev said was correct, that the Pal system no matter how you play it back, and irrespective of how it is recorded, MUST play back at 25fps, I do not own a laserdisc so cannot perform the same experiment, but I would put money on having the same result, as long as it is PAL. Obviously if it works between video and DVD it will also be the same VHS to VHS or DVD to DVD. I hope this has now put a line under what Kev has been trying to tell us all.

Chris. [Wink]

[Wink]

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Pedro Santos
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posted February 28, 2004 05:44 PM

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What requires a staight 25 fps framerate is the PAL television system that runs stricktly at 50 Hz. TV is not mulisync like computer monitors. They only run at 50 Hz (or the latest flicker-free tv sets, at 100 Hz). So, I cannot understand how a 26 fps output of a video source would look at a PAL tv. Obviously, sync-problems must occure, vertical moving black lines etc. The heart of any tv system always beats at a constant frequency. So, if you adapt the projector the the same frequency, with the same accurancy, there won´t be any sync problems.
Pedro

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John Whittle
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posted February 28, 2004 08:39 PM

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Pedro,

There are tricks to playing video at different frame rates. When we use a video playback that is to be photographed on 35mm motion picture film, we make a special video transfer at 24 fps which we play back on a special VCR. Older television sets would use the synchronizing pulses from the signal to run the display. Thus as long as you kept your math together you could do this. So for Hollywood we'd do a 24 fps transfer at 655 scan lines. That's what you see when you see a tv set running in a movie (unless it's a LCD screen that doesn't have that problem). The Panavision camera is phased before shooting the scene to roll the bar out.

As for trick play on laser discs. I'd have to see the manuals, but it sound more like the trick play that was worked out for tape as well where fields would be thrown out to match the sync and thus speed up the playback.

Some of the chips used in new tv sets make the 24 fps playback problematic and specially modified sets have to be used.

The think no one has addressed is the 4 per cent speed difference in sound pitch. If the DVD is made with pitch correction (at least that's the way I did PAL transfers for export) then when you re-record at 25 and play back at 24 the sound will be in synch but the pitch will be off.

It's quite jarring to me when I hear it speeded up, maybe it's just not objectionable to anyone doing re-reocrding so no one has commented.

John

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John Clancy
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posted March 01, 2004 03:32 AM

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John, most of us wouldn't notice the change in pitch unless we knew the film so well as to be able to tell. Very unlikely given we're only likely to learn the film well enough off a video source.

I spoke to Bob (who does the ticket desk at the BFCC) on Friday about this subject. He was even more confused as me with this anomaly with laser vision. I'll have to check it all out again. But I've definitely run the pulse from the laser disc and the film (which was synchronizing with the DVD) drifted out of sync' very quickly. That is where the confusion on my part has arisen. The Star Wars laser vision disc from 1982 needs looking at again as I haven't run it for some years; they definitely did something clever with it to fit it on the disc at the time.

Now then, I think I need one of these crystal boxes!!!

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John Whittle
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posted March 01, 2004 11:51 AM

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John,

I'm amazed that the pitch difference doesn't bother anyone. (I used to run the 35mm air prints of Starsky & Hutch, Charlies Angels & Vega$ at Movilab Hollywood and ship them to the BBC.)

Of course when we do a film transfer, we've just spent an eternity on the film at 24 fps and proper pitch and then to do the PAL transfer at 25 fps I have to put in a pitch correction or go crazy.

The problem with this is when you use that pitch corrected transfer (from video or dvd) as your source, it'll only sound correct if you run your projector at 25 fps. Maybe that's what normally happens--I don't know. It would be interesting to find out if you guys normally have your projectors running at 24 fps or 25 fps.

John

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Kevin Faulkner
Film God

Posts: 4071
From: Essex UK
Registered: Jun 2003

posted March 04, 2004 07:19 AM

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I never thought we would win the great Mr Clancy over on this one. [Wink]

[Wink]

When you can get your head round this 25 FPS and the PAL TV system it falls into place. Good test there Chris and when you think of it there is a lot of mechanical variations involved and it still runs at 25 FPS.

Kev [Wink]

[Wink]

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GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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John Clancy
Phenomenal Film Handler

Posts: 1954
From: Cornwall
Registered: Jun 2003

posted March 04, 2004 07:56 AM

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John, it probably drove you crazy because you knew the film well enough from 24fps and were therefore aware of the difference. As PAL runs at 25fps it is very unlikely anyone is going to know a film well enough to notice the marginal change.

Now Alien is another matter. I can tell every change simply because I know the film so well. As the sound wasn't particularly good on that title I rarely run it in sync' with the disc but when I do the change is perceptible to me; but I doubt anyone else over here would notice.

Kevin, I'm sure Mr. Wilton would like one of these Crystal boxes too. Could come in handy for certain soundtracks at the convention.

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British Film Collectors Convention home page www.bfcc.biz. The site is for the whole of the film collecting hobby and not just the BFCC.

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