Film-Tech Forum ARCHIVE: dealing with soundtrack damage

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Posted by Scott Norwood (Member # 30) on 02-13-2013, 09:12 AM:

I received a print yesterday with good picture, but with platter/roller scratches in the soundtrack. It is not quite unlistenable, but the soft crackling sound is annoying. Is there anything that can be done on the exhibition side of things to minimize the impact of the scratches? Specifically, is there any benefit to slightly de-focusing the optics or is there anything else that can be done?

This is a mono B&W print with a silver track. The theatre is using BACP LED readers.

I have the equipment and loops to re-do the A-chain properly after this screening if necessary.

Posted by Mitchell Dvoskin (Member # 751) on 02-13-2013, 09:20 AM:

Base side, FilmGuard, emulsion side, not much you can do.

Posted by Louis Bornwasser (Member # 3063) on 02-13-2013, 09:29 AM:

Try: using noise reduction even on mono.

shorting ONE channel input, then the other. (Older processors, remove one NR card, then the other.)

Best news of all, instantly back to normal. Louis

Posted by Randy Stankey (Member # 64) on 02-13-2013, 10:43 AM:

Sounds like bacon frying?

Not a whole lot you can do. Try FilmGuard. Even if the emulsion side is damaged, it will help a little. (Depends on how bad the scratches are.)

Try different modes: Stereo, mono, noise reduction in our out.

Past that, I can't recommend much else.
If its a movie that will only have a short run, realigning sound heads and tinkering with processors might prove to be counterproductive. You'll spend all that time changing stuff, only to restore it a short time later.

I would only consider making changes to the system if the movie is going to have a long run.

Posted by Sean Weitzel (Member # 244) on 02-13-2013, 11:15 AM:

I'm told LED readers exacerbate dirty or damaged tracks. One trick I've seen done is to put a piece of translucent adhesive (scotch) tape over the light source to diffuse the light somewhat.

Posted by Manny Knowles (Member # 1171) on 02-13-2013, 11:24 AM:

Is it an archival print?

You may not be permitted to apply a liquid cleaner, even if it will help. I'd ask first. [thumbsup]

I suspect Scott knows this, but I'm adding this note in case some future person finds this thread. It's likely that more and more prints will be sourced via archives as time passes.

This sounds like a situation where an additional layer of outboard EQ's (normally in bypass) might help. Engage them when you get into a "situation" like this, dial-in a setting that works, and then bypass them to return to normal.

Posted by Jack Theakston (Member # 4484) on 02-13-2013, 12:07 PM:

Is it a density or area track? If it's an area track, what kind?

Posted by Brad Miller (Member # 2) on 02-13-2013, 01:45 PM:

quote: Sean Weitzel
One trick I've seen done is to put a piece of translucent adhesive (scotch) tape over the light source to diffuse the light somewhat.

This works surprisingly well (I think I was the one who showed you) and is something I always do for film collectors or sub run houses that are working with used prints. Do note you will have to slightly increase your current to the LED and run tone again to calibrate, but the benefits of the Scotch tape far outweigh not having it. Keep in mind it must be Scotch tape (the kind that you can write on that looks frosted).

Sean, remember that old reel of film you brought over last year how clean it sounded? Scotch tape. [thumbsup]

Posted by Manny Knowles (Member # 1171) on 02-13-2013, 01:59 PM:

I just gotta try this!

Posted by Scott Norwood (Member # 30) on 02-13-2013, 02:13 PM:

I have not made a direct comparison, but I do feel that the LED readers are more sensitive to print damage than an exciter/slit-lens arrangement. Curiously, the same is true for cyan-track prints played with white-light readers. I know of a theatre that did this for a while before converting to LEDs. They actually sound OK (though noisy) if the print is new from the lab, but damaged cyan tracks sound terrible on a white-list reader system.

I will try the Scotch-tape thing tonight. Will also try playing in Dolby A and turning off the power amps for the other channels, which for some reason did not occur to me last night when I was testing things. Presumably the matrix decoding will help somewhat. Unfortunately, there is no way to create a matrix format without NR on the CP650.

The backup plan is to show a collector print, but it has a different set of issue.

Thanks for the suggestions.

Posted by Steve Guttag (Member # 268) on 02-13-2013, 06:24 PM:

LED readers are indeed more sensitive to scratches. The magic-tape theory does indeed work...I've done a couple of layers to get a very diffuse light...you definitely need to increase gain though.

Posted by Gordon McLeod (Member # 33) on 02-14-2013, 09:03 AM:

If it is a dolby dp50 100 or 200 it is possible to set the A type cards to act as a DNR noise filter Hopefully someone can remember how I cant find my book on that

Posted by Louis Bornwasser (Member # 3063) on 02-14-2013, 09:50 AM:

Gordon, you either set the level too low or too high. That is what you are thinking.

The Scotch tape thing does help with noise since it rolls off the highs and miscalibrates the dolby tone. Remove when done or you might as well have a Smart. (Don't think so? Run an A chain with the tape in place.) Louis

Posted by Sam D. Chavez (Member # 1841) on 02-14-2013, 10:18 AM:

Louis, your and my memory are going fast. But I do remember more than you about this issue.

You can engage the filter on the 50 and 200. On the 50 with the original pushbutton switches, one could engage or disengage the academy filter independently. The 100 is fading from my memory, but the 364 external NR for surrounds did have a half and full NR filter but only for the surrounds.

The 200 can be programmed to set a two stage filters one stage at a time. You have to create a custom format to do it.

As to the tape, it works but it lowers the Dolby reference. You need to re-do the level to get back up to Dolby level. It has nothing to do with cutting high or low end frequency response.

The best way to lower the sensitivity to dirt is to make sure the LED is right up close to the film, just sort of touching it. This has the effect of diffusion. For various mechanical reasons it is sometimes difficult to get that close.

Posted by Steve Guttag (Member # 268) on 02-14-2013, 04:43 PM:

As I recall, Dolby used the CAT 22 and then the CAT 280 like Gord was mentioning but in their 43 and then 430 series of processors.

The CAT 43/CAT 430 allowed one to have control over the expanders so one can get a DNR like noise reduction but with the flexibility of adding as much expansion as desired/needed.

Posted by Brad Miller (Member # 2) on 02-14-2013, 11:46 PM:

quote: Sam D. Chavez
As to the tape, it works but it lowers the Dolby reference. You need to re-do the level to get back up to Dolby level. It has nothing to do with cutting high or low end frequency response.

Sam is 100% correct here. There is no HF loss if the A-chain is calibrated after the tape is applied to the led. (We aren't applying it to the lens.)

Posted by Randy Stankey (Member # 64) on 02-15-2013, 08:39 AM:

I bet the tape changes the acutance of the optical system in the reader.

http://en.wikipedia.org/wiki/Acutance

Much the same as the difference between a diffusion-type photographic enlarger and a condenser-type. There is little difference between the two in terms of being able to produce a measurably sharp, clear image but the perceived sharpness is different. (Acutance.)

Because of the way a diffuse light "bends" (diffracts) around the edges of the dark/light areas on the film, a diffusion-type enlarger tends to hide the appearance of tiny bits of dust or fine scratches on the film.

My guess is that the same thing is happening inside the projector. [Smile]

Posted by Sam D. Chavez (Member # 1841) on 02-15-2013, 10:22 AM:

Randy is spot on here.

Posted by Randy Stankey (Member # 64) on 02-15-2013, 12:48 PM:

Here's an idea:

I have a Beseler 23C enlarger controlled by an Analyser Pro timer/densitometer.
If I have a problem negative with excessive dust that I can't get rid of, I would replace the clear glass heat filter with a piece of milk glass then recalibrate the densitometer to account for the difference in exposure and contrast. The Analyser Pro has saveable settings that I can recall when I need them. I would just recall the settings that I calibrated for when the diffusing glass is in place.

The diffuser costs me about a half stop of exposure and a half grade of contrast but the Analyser's settings compensate for it.

So... What if you got a small pice of frosted glass, about a half or a quarter inch square then created a small bracket to hold it in place when needed. You could make it from heavy, coat hanger wire and an alligator clip.

Then, since I can use a computer and software to store and recall settings on my Dolby CP650 processor, I would have one set of parameters saved for regular use and another set of parameters for use when the milk glass diffuser is in place.

Whenever I have a problem print, it would take about five minutes for me to make the switch.

In these days, when finding good, clean prints of a given movie might be difficult to impossible, this idea might come in handy.

Posted by Tony Bandiera Jr (Member # 2365) on 02-15-2013, 01:31 PM:

Another solution along the lines of Randy's excellent suggestion would be theatrical diffusion gels. Roscoe makes them, and if you request one of the swatch samples from them you'll get one big enough for two projectors' worth of diffusers. [Smile]

Posted by Randy Stankey (Member # 64) on 02-15-2013, 01:58 PM:

Considering the confined space inside many projector sound heads, a piece of glass and a bracket to support it might be a tight fit. A piece of glass in there could pose a risk of damage to the film. Theatrical gel sounds like a good, low cost solution that gives repeatable results.

If the processor is recalibrated when the gel is in place, it ought to be easy to recall those settings in your CP650 when needed yet still have "normal" settings available when the diffuser isn't needed.