Enhance 35mm optical mono sound?

[Brad Miller]

If you don't have a specific need to run cyan tracks, dump the awful red light entirely. They make everything (except cyan tracks) sound awful. Install an IR light source in its place and be done with it. This is what I've done in my room because I figure anything with a cyan track is also going to have some flavor of digital sound. I feel running a cyan print in digital without an analog backup is well worth the gamble of a digital dropout vs. having all other prints I run the analog track on sounding terrible.

[Emiel de Jong]

That's why I like this solution so much: this is a machine at the NFSA in Australia: the top penthouse reader is in fact the soundhead model used in a FP20 projector of the 1950's. The model of the bakelite exciter lamp holder dates even from the 1930's...

FP38ENFSACanberra-1.jpg

[Jerry G. Axelsson]

Hello Emiel,

Thank you for your input. I am aware of this solution. The projector in question I am looking to apply this solution on is a pair of DP70:s. At the same time I am trying not to over-complicate things.

If an older FP20 reader was fitted under the top spool-box of a DP70. There is the matter or digital delay for the sound. This can be accomplished, the question is how complicated this would be?

[Steve Guttag]

I'm not a huge fan of the traditional Philips/Kinoton analog soundhead. The cell "looks" forward and tends to pick up any light that is in the booth, including work lights. The drum is too small and tends to be more prone to flutter.

I seem to recall that BACP used to make a version of its digital penthouse but for reading optical sound (offset LED and cell). Obviously, Sam Chavez would know better if it existed and if any can be had, if they did. Penthouse solutions for DP70s are already "thought out" and the most engineering that would need to be done is, perhaps, cutting/drilling/tapping some aluminum plate to sandwich the the penthouse between the head and the magazine. Digital delays exist from various sources (though the delay times will be on the longish side) and think in terms of video latency type delays where you will need seconds, not milliseconds. Note, if you have cause to have a Q-SYS system in your sound, Q-SYS can have up to 60-seconds of delay in a single component block. The delay components can have multiple taps so you could set up several delays and just switch between them based on the frame rate of the movie. You could, even, have a variable delay on-the-fly, if you had the need to tweak for a print that isn't quite right (or reel).

[Sam Chavez]

Thanks Steve,

We did make an analog soundtrack reader version of the DSTR-20. We could do it again but on used DSTR-20 readers as we sold all the new stock DSTR-20's years ago.

As to DP70; a few places around Hollywood used two different versions of the soundheads. One with a Red reader and another with an IR LED. Mounting studs enabled plug and play although the soundhead weighs about 30 pounds.

[Emiel de Jong]

@ Jerry: digital delay wouldn't be the most complicated thing: that would be that you need an extra feed sprocket before the soundhead if you install a FP20 soundhead as a penthouse.

Furthermore Steve is right about the possible problems with the FP20 soundhead. I would go with the older design, in fact as it is in a DP70 with unchanged 35mm optical sound. There are some issues: weave: originally the shaft of the pressure roller is intentionally not exactly in line with the sound drum so the film moves to one side of the pressure roller and stays there. It's my guess this effect diminishes when the soundhead gets older and there starts to be some play in the parts: more weave. If I remember correctly Mark Gulbrandsen solved this problem once by splitting the pressure roller. Also the original brass slit mask isn't allowing much high frequencies, but a less wide one is easily made with laser cutting nowadays.

So when you can find an extra optical soundhead, or still have the original, constructing something that makes swapping soundheads "easy", like Sam mentioned, could be an excellent solution.

[Steve Guttag]

Yeah, probably, if the original analog soundheads are not too molested, using them for optical sound and a normal penthouse reader for digital would be best. As for the DP70 optical slit, some just printed a narrower slit on transparency to make an additional mask to get more high frequency. The pinch roller on the DP70 skewed so that it hit the inboard side first. this would tend to force the film to the outside. It worked reasonably well. The weave wasn't too bad. While you could see it in the peep hole, if one ran crosstalk film (CAT97), you never got any crosstalk and Buzz Track could be run without getting alternating high/low tones so it wasn't bad enough that it should alter sound quality. It isn't like the other soundheads were perfect either and neither was printing or especially the doping of the soundtrack...ever watch how erratic the doping was by pulling the aperture plate on conventional projectors to see it projected? Talk about a drunken sailor!

[Jerry G. Axelsson]

Steve and Emiel, our DP70:s has the modern Kinoton reverse-scan readers with SRD. One feature which we plan to add is the side-steering of the pressure roller like on the older Philips soundhead.
If we get that feature in place we can reach further with them than in current state. We still have the red-led though. I do also have two original soundheads which are in ok shape. Needs to be renovated I would say. If you could choose one light source on the soundhead which is most flexible in overall performance. What would that be? White LED for ALL optical tracks?

We still play a lot of analog prints. Most are in mono. The trick of course is to find an improvement which does not have a drawback on sound quality in other formats.
Remember, we are an archival cinema and play films of all sorts from 1,19 Movietone to A/SR/SR-D/DTS.

[Emiel de Jong]

I wouldn't change something to the Kinoton reverse-scan readers, unless there's something wrong of course. And I think the side steering effect is already there: the pressure roller presses the film down on the sound drum just on one side of the drum. I cannot say anything about white leds because I never worked with them. I know it's not just the white color: it's the infrared, like exciter lamps generate, you need too. Personally I would stick with exciter lamps.... Then use that old fashioned sound head for the older movies, swap it to the Kinoton reverse scan for all else. Making the soundheads swappable is of course a small challenge...

[Sam Chavez]

The Norelco sound lenses were far from perfect. The slit was a bit too short, so had trouble with sound at full modulation. You ended up with a bit of amplitude modulation. You can't reproduce the soundtrack edges if you don't light them. Lenses in American projectors were better in this regard. The Dolby Illumination uniformity test film showed this very clearly.

As Steve mentioned, the lay down roller on DP70 as well as FP20 and DP75 were all tilted to bias the film outward. Century did this as well by tapering the sound drum about a .0001 to bias the film.

[Steve Guttag]

For the Century, it was probably just bad machining. They couldn't even get their guide arms to move up/down and maintain lateral position. .

The RSSD version of the sound head by Kinoton doesn't use the skewed roller (I think the original rollers were skewed in two directions so it forced the film to the outboard and also only contact the roller at one point. The RSSD, when thens are set up right (correct pressure), tends to have the film almost float as it goes around the soundhead with a slight pucker as it feeds the pinch roller. Depending on the machine, they also would put a damped roller (had a damped piston on it) to also smooth out its action.

As for what light to use, the cell is most sensitive to Infrared. I'm not convinced that a white LED is an answer to a "what is best." First off, what is white for an LED? Have you done a spectrum analysis to know just what colors are present? As I recall, a white LED is a blue LED doped yellow. However, more to the point, one of the keys of a traditional tungsten lamp is how the light interacts with the film, particularly scratches in the soundtrack area. Because the light rays scatter every which way, scratches are more subdued as they don't create a shadow on the cell. With LEDs, the light is very collimated so any scratch will tend to have a very distinct line and create a noisier sound.

The other issue is that if you have a traditional color-film soundtrack (made with just the yellow layer, as I recall, and then the application is put on for the traditional very contrasty track), RED LEDs will get a notable cross-modulation distortion that sounds quite harsh. Furthermore, it isn't uniform from reel-to-reel, let alone print-to-print. The only time you NEED red light is for the modern cyan tracks. This is one of the reasons I really fought against the adoption of cyan tracks red LEDs. Film was clearly at the end of its run. It was a last-ditch attempt to make film more ecological and less costly during its last 10-years of a 100-year run. However, as a legacy, it now requires every theatre that handles film to consider how to best handle almost all of the titles...and then that last 10-years. It was never going to prolong film's continued use as a mainstream medium. The economics of digital were taking their own path and once viable, the change was inevitable. The same will be true for emissive "TVs" versus projectors. It's not if, it is when and $$$ will dictate that.

Anyway, so if I were trying to handle non-cyan tracks, I'd go with IR LEDs, presuming you can locate some. You could take Brad Miller's approach of just not running cyan tracks since there should be a digital track for those titles or put in one of Sam's penthouses that are modified to handle the analog track but with IR LEDs. One should note, swapping LEDs is not a trivial thing, even if you have interchangeable LED heads, like on the DSTR-20. The index of refraction comes into play with IR light versus visible red. Your focus will be off and HF will suffer if you don't optimize for both light sources. I have also found that a way to desensitize an IR system to scratches on analog tracks is to put some Scotch Magic Tape on the IR LED to create a diffuser. There is normally plenty of gain left over on an IR system since the cell is VERY sensitive to that light.

At the Library of Congress in Culpeper, VA, they have four film projectors in their main theatre (two 35/70s and two 35/16s) and I opted to outfit two with visible red and two with IR so that based on the type of track, just like with the gauge of the film, they can choose to use the most appropriate pair. Another nice thing about the IR LEDs...when I do my annual PM calls there, the IR levels NEVER drift. They are much more stable and can be driven less hard. Less current = less heat = longer life/stability for LEDs. Alas, 4-projector plus digital is not a luxury most cinemas have the space for, even if they wanted to! Furthermore, with that many projectors, keystone can be a challenge.

[Sam Chavez]

The Dolby LEDs were designed as arrays (2x12 individual LEDs) to produce non-collimated light to avoid the issues with dirt and scratches. A point source LED produces collimated light and has the issues Steve mentions with soundtrack dirt and scratches. That's one reason Dolby style LEDs ars $50.00 while simgle point source LEDs cost perhaps a dime by comparison. The reverse scan method is superior way to read the film soundtrack to front scan. Western Electric knew this. The source and color of the light is a different matter altogether. Also, at the time when the decision led by Dolby and projector manufacturers to go reverse scan and basement digital reader it was not known that DLP projectors would win out. It indeed took over, partly because of 3D playback and also because cinema owners signed their lives away with the VPF. That part was not inevitable.

[Jerry G. Axelsson]

Sam, a great thank you for your input also. So I am leaning towards keeping the Kinoton rev. scan readers on our DP70:s. Our former main technician reminded me of the previous weave and flutter on the Philips soundheads which was original. I do not feel like reliving that part of history. Sam, if you could modify this towards one lights source other than red led. What would you recommend?

[Sam Chavez]

Jerry,

At this late date I would go for the IR as there are more prints of interest to play that were made before the Cyan tracks came along. The problem is there are no more IR LED arrays around. I still stock the Dolby red LEDs and have enough for quite a while. And there are knock offs out there as well, but not for the IR type. So theres really not a perfect answer.

I don't want to get into a pissing contest with our patron Brad Miller but I don't agree that red LEDs sound terrible. Overall, the reverse scan method gives improved audio fidelity over front scan, but nothing about analog optical sound is perfect. Best case 3% distortion.

I will offer an example to show the real time use. Several museums and university film centers bought BACP analog readers with interchangeable Red and IR light sources. In all cases I know of, the staff decided the Red LEDs were fine for all tracks and never actually bothered to use the IR LED modules.

[Emiel de Jong]

The Norelco sound lenses were far from perfect. The slit was a bit too short, so had trouble with sound at full modulation. You ended up with a bit of amplitude modulation. You can't reproduce the soundtrack edges if you don't light them. Lenses in American projectors were better in this regard. The Dolby Illumination uniformity test film showed this very clearly.

Very interesting. This slit being a bit too short, did you encounter that on both the newer ("FP20") and the older ("DP70" / reverse scan) Norelco / Philips soundheads?