Film-Tech Forum ARCHIVE: OK to run non-striped film over mag head?

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Posted by Gary A. Hoselton (Member # 3447) on 08-04-2018, 06:01 PM:

I have Siimplex 4-track mag readers atop my XL's. What is effect of running non-stripped film over the heads? Has to do with making up shorts on a reel, where some footage is sound-stripped and other footage not. What were the rules and practice?

Posted by Stephan Shelley (Member # 8587) on 08-04-2018, 06:08 PM:

excessive ware on the hard to replace mag heads. Your going to scratch the outboard half of the optical soundtrack. 4 track mag covers half of this with a mag strip for center channel.

Posted by Phillip Grace (Member # 2262) on 08-05-2018, 01:40 AM:

The convention when inserting junk film as spacing into sound component reels for rerecording was to splice it in so that the base surface, not the emulsion, ran across the magnetic heads. This would have been done to protect the heads, rather than the film. For 35mm film the optical and magnetic sound tracks are on opposite sides of the film base. A small degree of scratching to the base side of the optical track should make little or no difference to the sound reproduction on either front or rear-scanning soundheads. Variations in the emulsion geometry on 16mm film would require further consideration. That being said, I would expect that magnetic heads in good condition would not damage the film anyway.

Posted by Frank Angel (Member # 248) on 08-06-2018, 07:01 PM:

Why would you thread around the heads? Normally if the penthouse is situated properly on top of the XLs, you should be able to threat directly thru the penthouse and bypass the heads entirely. And yes, if you must threat around the heads, protect them from direct contact, but even with a wrap of film, you will be adding unnecessary friction against the film emulsion.

Posted by Gary A. Hoselton (Member # 3447) on 08-06-2018, 08:11 PM:

Frank, my query has to do with combining some soundstriped film with non-striped film on same reel, such as
1) optical-only cartoon, then 4-track short, then optical-only preview, or
2) Mono optical reel with 4-track entrance, entre acte, or exit music spliced on. Or,
3) four-track reel with entrance, entre acte, or exit music only available in optical mono. Etc.
If safe to mix mag and non-mag on one reel, would save a changeover or two for fairly short run times. But, "Do No Harm" is the prevailing admonition, so am I safe combining or not?

Posted by Tony Bandiera Jr (Member # 2365) on 08-06-2018, 09:07 PM:

Gary, short and direct answer is NO, it is not good to mix mag and optical on the same reel.

I disagree strongly with Phillip on the idea that "A small degree of scratching to the base side of the optical track should make little or no difference to the sound reproduction on either front or rear-scanning soundheads."

ANY scratching on an optical track, base side or emulsion side, WILL introduce audible degradation to the track. (How audible is subject to which side of the film and how severe the scratching is of course.)

I firmly believe that you should always take the utmost care of ANY film, whether in your personal collection or especially if it does not belong to you.

When I worked the University some years ago, I would even do changeovers for just the Dolby SR/Dolby digital snipes as I was often dealing with archival or privately owned prints. It does not take that much more effort to do the changeovers, especially if you are only dealing with a few shorts.

If you are doing a program of several minutes (>20mins.) or a few HOURS of shorts, then try to program them so that all of the compatible tracks are on individual reels for the changeovers. I have found that, with rare exception, most filmmakers (or as at UCI, professors) will adjust the program order willingly to preserve the film itself and improve the potential quality of the presentation.

Posted by Leo Enticknap (Member # 534) on 08-06-2018, 10:12 PM:

Just to underline what others have written above, I was taught never, ever, to run unstriped film over a mag head (because the raw film base will cause abrasion damage to the surface of the heads), or striped film through an optical head (because the pad roller that guides the film over the optical scanning drum may apply enough force to damage the oxide).

I can't ever remember being in a situation in which I was asked to run striped and unstriped film spliced together in the same reel. If I ever had been, I'd have explained the situation diplomatically to the film's owner, and asked for his or her permission to unpick it and resplice it into a striped and an unstriped reel, if only temporarily for that show. If they had refused, it would have been up to the house manager as to whether or not (s)he was willing to risk damage to the equipment running it as is.

The nearest I've come is having to run acetate and polyester spliced together in the same reel, and having to ride the gate tension on the fly in between individual clips.

Posted by Phillip Grace (Member # 2262) on 08-08-2018, 03:17 AM:

Well, that's me told! [Smile]

I assumed a single projector was all that was available. Given a dual projector change-over system there is no reason to take the risk - thread appropriately to the film to be screened and change back and forth as required. Maybe make up more or less synchronized rolls if the times involved between changes are too short to re-thread the incoming machine.
I'm curious though, as to why raw film base would be more abrasive than applied magnetic stripe material.

Posted by Scott Norwood (Member # 30) on 08-08-2018, 07:16 AM:

Running the base side of unstriped film over mag heads is done all the time in postproduction, where junk picture film is used as leader and "sound fill" in rolls of mag-stripe film. This should cause no more damage to the heads (and possibly less) than running mag film across them. Running emulsion-side against mag heads is bad, though.

Unless the mag heads in dubbers are significantly different from the mag heads in projectors, this shouldn't be a problem. I have seen mixed rolls of 70mm mag and 70mm DTS run together with no obvious problems, as the 70mm mag head only touches unprojected film area.

As mentioned above, this may be a problem with 35mm, since the mag stripe is located over part of where the optical track would normally live.

Also, with 35mm, there is the issue of mixing CS perfs and KS perfs in the same roll. This might actually work if the film is cement-spliced together, but I'm not sure that I would want to try it, personally.

Edit: Aside from this thread, I have never seen or heard anything about not running mag film through an optical head. And I'm not really sure how one could avoid doing that with 35mm on any projector other than a Norelco. Why would this be a problem, assuming that all of the metal parts have been demagnetized?

Posted by Monte L Fullmer (Member # 2797) on 08-08-2018, 03:56 PM:

Just make up separate reels - to be safe.

New mag heads are unobtanium.

When I ran a booth with full Simplex DeLuxe Stereo XL setup, our preview reel was separate from the mag stock and we would never splice optical on a mag roll for the same purpose of limiting wear on the mag heads.

quote: Scott Norwood
Also, with 35mm, there is the issue of mixing CS perfs and KS perfs in the same roll. This might actually work if the film is cement-spliced together, but I'm not sure that I would want to try it, personally.

In the mag days, Griswold did have a mag slicer (grey frame instead of black) that had CS register pins instead of the larger KS pins where one could wet splice both stocks together.

CIRO also had a CS tape splicer to do the same. Frame was gold instead of aluminum.

If using a standard KS pin splicer, then one is going to have to file down the pins for the CS sprockets to do both stocks.

Posted by Leo Enticknap (Member # 534) on 08-08-2018, 04:19 PM:

quote: Scott Norwood
Also, with 35mm, there is the issue of mixing CS perfs and KS perfs in the same roll. This might actually work if the film is cement-spliced together, but I'm not sure that I would want to try it, personally.

+1. Added to which, any CS-perforated stock in circulation now is likely to be significantly shrunk. I would want to run a section of leader to check for perf damage before running a reel, even with sprocket teeth that are designed for use with CS perfs. That having been said, I was playing probably three or four CS prints a year on the Egyptian's Norelco AAIIs, and there was no problem with any of them.

Posted by Gary A. Hoselton (Member # 3447) on 08-11-2018, 12:42 PM:

Thanks fellows, you have given me a policy for my booth:

1. OK when needed to splice non-soundstriped CD leader and head and tail leaders to 3- and 4-track soundstriped 35mm film, oriented so that only base side contacts the heads.
2. Do not combine soundstriped and non-soundstriped program material on the same reel, but arrange them for changeovers.

Objective is to extend life of mag heads and avoid possible scratching by surround track head on base side of optical track of non-soundstriped film.

Posted by Gary A. Hoselton (Member # 3447) on 08-11-2018, 06:59 PM:

I misidentified mag track laid over half the optical track, and time to edit has expired. Post should be:

Thanks fellows, you have given me a policy for my booth:

1. OK when needed to splice non-soundstriped CD leader and head and tail leaders to 3- and 4-track soundstriped 35mm film, oriented so that only base side contacts the heads.
2. Do not combine soundstriped and non-soundstriped program material on the same reel, but arrange them for changeovers.

Objective is to extend life of mag heads and avoid possible scratching on base side of non-soundstriped film by track 2 center speaker head which rides on the stripe that covers half of the optical sound track.

Posted by Frank Angel (Member # 248) on 08-13-2018, 06:16 PM:

I just ran a few reels of 2001 4trk and it played without any problems (original release print 1968, but it is Eastman, so in the non-IBTech universe, space is beet red. What a shame. Sound on the other hand is still awesome except for the "inaudible" 12KHz trigger every now and then. What duffus thought THAT was a good idea? 25Hz would have worked just as well and a lot less likely to be reproduced in those little surround speakers of the day. You can notch that 12KHz all you want but every time I am in the house I want to hold my hands up against my ears like the guys on the moon when they are inspecting the monolith. [Embarrassed]

Posted by Sam D. Chavez (Member # 1841) on 08-13-2018, 08:54 PM:

Congrats on being able to hear 12 Khz at your age. LOL

The filters used to notch this were none too good mostly, and there is the issue of the projector not running on speed. So the 12Khz is off to one side of the notch filter.

Posted by Frank Angel (Member # 248) on 08-14-2018, 03:49 AM:

12kHz...no one will hear that.

Posted by Steve Guttag (Member # 268) on 08-14-2018, 07:34 AM:

Well...

There were flaws in the plan. First, I don't agree on the 25Hz thing because...you'd blow up the little surrounds of the day on any that leaked through and waste what little of your 5-watt amp doing it.

They got it backwards though...when the tone is playing, turn the surrounds OFF.

Remember too, the surrounds/effects speakers of the day were not too good, by design at 12KHz so in addition to the notch filters, you had the speaker itself not reproducing it so well.

It clearly wasn't the best system and yes, I too still hear it and find it most annoying. I believe, with modern DSP technology, it would be possible to bury it. I'd combine a couple of notch filters in and around the 12KHz area as well as low-pass the track. There is nothing in the high-end there anyway.

Posted by Steve Roberts (Member # 9544) on 08-15-2018, 04:38 AM:

I hate to throw a spanner in the works as it were but, in the UK in the late 1960's there was a 3 track mag advert. If we had a 70mm or Cinemascope trailer then the mag advert was left in with the rest of the opt advert so we would thread both mag and opt sound heads.

Magnetic heads for 35mm 4 track and 70mm 6 track are still available NEW in the UK from Summertone.com

As to the 12K tone, I am well over 60 I can still hear it very well. Apart from my own mag set up (CP200) I service a Westrex 4 track set in one of my friends home cinema. We installed the set in 1973 with all the original speakers including the 6 Westrex effects cabinets. The amps are 4 Westrex 2042.