Film-Tech Forum ARCHIVE: Visible Red LED Reader Compatibility with Vintage 35mm Prints

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Posted by Cris Capp (Member # 5476) on 10-19-2009, 03:20 PM:

Hi everyone,

This is my first post here at Film Tech and I have a few questions for you all. Please go easy on me as I am a bit of a newbie when it comes to cinema technology!

1. Is there a difference between ‘redeveloped silver soundtrack’ prints and old original vintage/classic 35mm prints? Or are they one and the same?
2. Are the Analogue LED Sound Readers, such as the BACP RSTR-2000, compatible with very old original classic prints? Is there any loss of audio quality while playing a vintage film?

So I understand that new cyan dye soundtracks require the LED readers. But I also read that the visible red LED is a compromise between old and new print technologies… and that by upgrading to the new visible Red LED’s I might actually have to sacrifice some sound quality when I show old vintage prints. I’ve heard that some archival presenters actually prefer the infrared LED’s to the visible red LED’s, is this true? My problem is that I have to show both- vintage films and new cyan dye films.

From what I understand- the negative density affects amplitude of the sound signal… so I visible red LED used on a silver soundtrack results in less amplitude than a tungsten white light reader.

This is taken from http://www.dyetracks.org/ci.os.0012.reddye.html

Table 1 – Summary of Print Color Balances for Soundtracks

Color Balance
Target Densities Negative
Density Recommended
Negative Density

IR Y C M

Silver
(Redeveloped) 1.40 1.64 3.37 3.58 2.18 2.20
High Magenta
(Redeveloped) 1.09 1.44 2.02 3.82 2.88 2.70
Cyan
(Dye) 0.36 0.36 2.14 0.38 2.60 2.70

Noise Performance
“Tests have demonstrated that readers based on broad band tungsten, or white light, illumination sources are quieter than readers based on narrow band red LED illumination sources (660 ± 20 nm light energy spectrum). It is believed that this is due to the fact that when the track is illuminated by broad spectrum white light, the incoherent noise sources from each of the film's color layers add on a random basis and thus the noise "averages out." If a narrow spectral band illumination system is employed, this averaging cannot take place and thus the signal-to-noise ratio is impaired. This is true whether a standard silver track, high-magenta applicated track, or cyan dye track is being presented. It is also independent of the type of release stock employed.”
http://www.dyetracks.org/ci.os.0012.reddye.html

Posted by Robert Minichino (Member # 3495) on 10-19-2009, 03:34 PM:

The redeveloped silver sound tracks (on color film) are effectively the same as on vintage color and B&W prints. We have RSTR-2000 readers and we mostly play older films; both variable area and variable density have worked great.

Posted by Mitchell Dvoskin (Member # 751) on 10-19-2009, 05:01 PM:

You may have problems using a red LED reader for some old variable density tracks. They work fine for variable area tracks. Fortunately, most older films have variable area tracks.

Posted by Damien Taylor (Member # 4255) on 10-19-2009, 06:36 PM:

Sometimes we have to bump the volume up on silver prints, which seems counter intuitive, but other than that they work fine.

Posted by Cris Capp (Member # 5476) on 10-19-2009, 07:13 PM:

How about when I get a film that has aged and turned a magenta pink color? We often show old prints from various studio archives that haven't been pulled out of a film can in years... and occassionally we get pink prints. I'm reading now that magenta films will have no sound when played with red LED's.

I'm having the feeling I want to keep my traditional exciter lamps in conjunction with upgrading to red LED. I have a Simplex Model 5 Star Sound Mechanism. And the projectors themselves are Simplex 35 Model PR1014.

Does BACP make a penthouse Analogue LED Reader? Is it even possible to have analogue reader in a penthouse configuration? I only have a CP65 Processor... and no sources for a DA20... and no budget for a CP650 so I'm not planning to go digital anytime soon. How can I best configure my system to play with both tungsten exciter lamps and red LED readers? My room acoustics are very harsh so that's why I'm concerned about any drop in audio quality in relation to whatever upgrade we finally choose.

Posted by Jim Cassedy (Member # 4115) on 10-19-2009, 09:13 PM:

Several years ago I ran a LOT of vintage prints at
an older theater that still had a mono sound system.
I had no trouble, even on very pink prints, when they
upgraded to the "red readers", except as someone else
noted on SOME variable density sound tracks. Mostly
those that had VD tracks which were low in contrast.

But this was an infrequent occurance. I can think of
only two times in almost 3 years that this issue
came up. We simply had to turn up the volume a bit
more, which increased background noise & hiss from
both the old tracks and the aging sound system.

Chances are I'd have had some problems with theses
particular tracks even with exciter lamp readers.

This was a "change-over" house with two projectos.
When we were installing the red-readers, I first did
one projector and then we ran a few we"ear" tests where
we did changeovers between the projector with the new
red-readers and the unmodifed one which still had the
exciter lamp type, since we had the same concerns as you
have about being able to play some of the older sound tracks.

I didn't have time to do full audio-electronic analysis
of the sound between the two types, but simple 'ear' tests,
with several diffrent prints and types of tracks showed the
difference between the two readers to be pretty much negligible
and often totally inaudible at our location.

(I don't mean the sound track was inaudible- I mean
that there was ofen no audible difference between the
two readers in a simple listening test)

Posted by Monte L Fullmer (Member # 2797) on 10-19-2009, 09:39 PM:

quote: Cris Capp
Does BACP make a penthouse Analogue LED Reader?

In the real sense, it wouldn't work since the analog track is recorded 21 frames ahead of the picture and in marketing terms, it wouldn't be feasable to create any such hardware/software to delay the sound information backwards from the optical track to match picture frame since there is no definite need, nor demand for it.

Now, if someone who is electronic smart could conger up such a delaying device for a creation of a penthouse optical readers (or even a convienient swapping from LED to filament bulb for the basement end of the spectrum) so one could have both worlds - exciter and LED playbacks, but then the user would have to pay up the nose to have one custom built for such an occasion..

Also, if you can find a white LED to swap out in a RSLH-2 module along with having the stock RSLH-2 LED module (since they're so danged easy to change out, but you might have fits with your pre-amp settings by lowering the gain down some using white light...), then this form of swapout could be more feasable.

-Monte

Posted by Mark Gulbrandsen (Member # 72) on 10-19-2009, 10:00 PM:

Typically they will sound much cleaner. You will also be hearing all the recorded frequenbcy the film is able to muster up. The only tracks they won't play straight out of the gate are old push pull and some off types of single unilateral variable area tracks. BTW: You should be able to play push pull if you re-wire the reader to do so.

Mark

Posted by Christopher Seo (Member # 7) on 10-20-2009, 01:16 AM:

Actually (as was mentioned before somewhere) there is at least one company, Sondor, which manufactures a penthouse that accomodates a red LED optical reader (with digital delay). Dolby Digital and DTS are also available. Here's the link. I would think it's pretty expensive though. With effort, some kind of home-brew solution could work. For example, an analog/digital basement reader could possibly be modified for dual red/infrared optical pickups. I also recall that Component Engineering made a basement reader that used white light for the digital, which could again be modified for another analog pickup.

I've run many older prints on red readers, and the sound quality has generally been good to excellent. However, there are occasions when I've wondered if white light would produce a better result, such as with noisy or sibilant tracks. I've never encountered an unplayable track. There's certainly no need to worry about faded prints, since the redeveloped track has silver and does not fade along with the picture. The single-unilateral variable-area tracks I've come across play fine as well (and I think that would be a stereo pickup issue in general).

Ultimately, it would be nice to have both white and red readers, but red light is necessary for newer prints and reverse scan is best for all prints.

Posted by Robert Minichino (Member # 3495) on 10-20-2009, 07:28 AM:

quote: Monte L Fullmer
In the real sense, it wouldn't work since the analog track is recorded 21 frames ahead of the picture and in marketing terms, it wouldn't be feasable to create any such hardware/software to delay the sound information backwards from the optical track to match picture frame since there is no definite need, nor demand for it.

Once you had a way to handle the film and mount the reader, all you would need would be an off-the-shelf digital delay.

Posted by Richard P. May (Member # 3598) on 10-20-2009, 09:37 AM:

To speak from the viewpoint of a restoration lab, the red LED readers work just fine with everything we've thrown at them. We are working with tracks as far back as 1929 variable density.
The only problem I have ever run into has been a color restoration with a VD track, printed with the now obsolete hi-magenta system. The magenta in the track filtered out enough of the red exciter light to make the track very poor.
This was most evident several years ago, when I was at WB. We restored a 1938 short subject, shot in Technicolor. The musical sections were variable area, and the dialog density. The area played just fine, but the density dropped way down. It was necessary to reprint changing the filters in the sound head of the printing machine, to alter the color of the track.
Other than this, I'd say don't be concerned.

Posted by Louis Bornwasser (Member # 3063) on 10-20-2009, 10:23 AM:

I have heard some complaints, but in every case, it was possible to get proper operation with critical alignment.

I guess what I am saying is that the reader was not "perfectly" installed at first. When tweaked, it worked just fine. Apparenly there is some latitude in non-critical playback of current films. Louis

Posted by Robert Minichino (Member # 3495) on 10-20-2009, 10:47 AM:

We ran a print with a silver VD track earlier this month on our RSTR-2000 readers and it sounded great.

Posted by Sam D. Chavez (Member # 1841) on 10-20-2009, 10:52 AM:

To answer Monte, we have made a couple of penthouse analog readers and it's really quite easy to modify the DSTR-20 to play analog tracks. It's then a snap to install either a standard red LED bracket (RSLH-2) or the Infra Red module (RSLH-2IR)with two screws.

There is a very slight issue with the absolute focus point changes between the two LEDs. It's fairly trivial amount like maybe 2 dB at 14 Khz so I would keep the RED in best focus and if you play a 70 year old silver print a tiny bit out of focus, it's our little secret, or you can split the difference.

The real issue is sync and there are stereo, variable delay, phase coherent delay lines out there that can deal with this.

I can hear Guttag winding up to correct me as I write.

Posted by Steve Guttag (Member # 268) on 10-20-2009, 11:27 AM:

What? Did I hear my name?

Facts and fiction run again.

The Visible red LED will work fine with many soundtracks. Certainly they play fine with cyan tracks...they also do okay with High Magenta. I haven't had a problem with them on B&W tracks either.

On magenta VD tracks they don't really work. Where they are a crap shoot are on normal color stock films with a regular redeveloped sound track. Some play okay others have horrible cross-mod distortion.

It isn't that you don't get audio but it is VERY harsh...it can sound like you amp is clipping even though you are not over modulating anything. If any of you have the DTS test reel that was made before the cyan crap came along (Dolby-A analog track)...listen to that reel in analog on a red reader...it will show cross-mod distortion pretty well (ours sure does).

What some people consider good/acceptable and even correct amazes me. A red reader on a print exhibiting cross-mod distortion is nasty to my ears.

We have some facilities that cater to the older moves that have IR LEDs. We had one facility that had IR we switched to visible for cyan tracks and the next conventional track they got their curator asked about putting the IRs back because the soundtrack didn't sound right (it was the cross mod distortion). But again, it is a crap shoot...some prints DO play fine on either reader...some don't.

As for the refocus between IR and visible...it is more than a dB or two at 14K...it is pretty dramatic, really. I'm sure it varies by lens design too.

Steve

Posted by Brad Miller (Member # 2) on 10-20-2009, 01:50 PM:

So Steve, what digital delay line would you recommend for such a low level signal, assuming a penthouse analog reader was being used?

Posted by Robert Minichino (Member # 3495) on 10-20-2009, 02:44 PM:

Any digital delay that works with a mic-level signal would work fine. On the cheap end, the Behringer Shark is a cool little tool and I've had good luck with them in the past.

Posted by Christopher Seo (Member # 7) on 10-21-2009, 02:23 PM:

With some (a lot of?) modification to the sound processor, one could insert the delay lines after the preamp. My understanding of the solar cells as current sources is minimal, but I would guess that feeding the optical pickup to the preamp and then performing the delay is the ideal method.