Old 35mm Sound Alignment Films - Query

[Phillip Grace]

Hi all. I have come across a can of old 35mm sound test films which included the following set of loops. They all have handwritten labels (see below) and seem to be an incomplete set. They are all on Safety Film base.


A - 400 Hz 50% Optical (KS perforations)

B - 35 Hz HI Optical (KS perforations)

C - 35 Hz LO Optical (KS perforations)

D - 25 Hz Optical (KS perforations)

F - 400 Hz 50% Optical (KS perforations)
35 Hz LO
25 Hz HI

I - 400 Hz 50% with optical
15 Secs No Signal
35 Hz LO
25 Hz HI

This last one is 4 track Mag/Optical with Cinemascope perforations.


Does anyone have any idea how this set of test films was meant to be used? They seem to be out of the ordinary range of optical sound alignment films, possibly for some kind of special evaluation or process. They were found in a country cinema, along with some old projection equipment including parts of RCA rotary stabilized sound heads, and the remains of some Western Electric Universal Bases. There was also a quantity of original Cinemascope picture alignment film. The location was a bit remote from major towns and the management always tried to be technically self-sufficient. I'm puzzled especially as to why there are the very low-frequency loops.
Any insight will be welcome.

[Sam Chavez]

I first thought Sensuround which preceded Dolby Labs and its test tone films. Also, perhaps more likely, Perspectasound (steered optical mono) which used low freq. tones to trigger its modes. You can hear the trigger tones on some 35mm cartoon prints to this day. That's my best guess.

[Steve Guttag]

What would be odd for Perspecta is...no third tone. Furthermore, Perspecta used 30, 35 and 40Hz.

[Sam Chavez]

There's no third tone present. Maybe it used to be part of the set and is now missing. I posted to stimulate debate. Whats your best guess? So far you're the only other person to post.

Perhaps pictures of the test films would be helpful.

[Steve Guttag]

I don't recall what Sensurround used...perhaps you were onto something there. I don't recall Perspecta fooling with 400Hz either and they tended to be for optical sound more than magnetic, yet he has a magnetic...which would be odd in the Perspecta era as if 4-track was available, why Perspecta.

It's something else...again, maybe Sensurround.

[Jim Cassedy]

<edited> I don't recall what Sensurround used...

When I originally saw this post, Perspecta was the first thing I thought of, - - but the frequencies are
wrong for that. I ran alotta Sensurround films a long time ago, and it used 25 & 35hz tones to trigger
the Sensurround decoderthingy. So that sort of matches a couple of the loops he has. Another thing
that might be helpful is if Phillip can spot any date-codes on the loops. Knowing what era they are from,
might give an additional clue as to what they might have been used for.

[Tony Bandiera Jr]

Perhaps the 400hz was for testing and balancing mono levels in a changeover booth, as well as possibly looking at distortion/wow/flutter too? The lower freqs could check the Academy filter?

On the mag/opt, trigger tones for the surround channel?

[Sam Chavez]

Sensuround kept changing technically from first to last release. I believe there were mag prints as well. There's also Tommy? It came out in optical and mag. Quintaphonic Maybe?

[Mark Gulbrandsen]

Here is a scan of a an actual Perspecta test film... You can hear it in a sort of pseudo stereo too. It's also exactly the same age as I am...

[Phillip Grace]

Thanks to all for your input!

After a day reading and following your leads it looks very like these are the alignment films for Sensurround - the existence of the Mag/Optical loop being the major clue. I will check the date codes to see if they might correspond to the release dates of the features.

The print inventory for "Earthquake" which used the Model 1 system included 35mm 4-track Mag/Opt. prints. The 25 Hz and 35 Hz control tones for the Sub Bass effects generator were placed on the optical track, separate from the program sound, and were the only content on the optical track. The Mag. tracks contained program sound, and I believe that track 4 included 12khz switching tones so that the Mag/Opt prints could be screened on conventional Magnetic sound systems, without the Sensurround effects. The 35mm Sensurround prints with Mono Optical sound track only, contained the 25 Hz and 35 Hz control tones for the effects generator recorded sub-audibly, and filtered out in a similar way to the Perspecta system. That might explain why the tones on the Mag/Opt. prints were of such very low frequency, even though that was not strictly necessary. Apparently there were installation issues arising from the difficulty involved in reading the low frequency tones through some of the theatre sound systems which existed at the time.

The Sensurround Model 2 system was developed for the release of "The Battle of Midway". The 35mm prints for this feature were supplied only with Optical sound. There were "Sensurround" and conventional Mono versions. Technical improvements in the system allowed for the Low Frequency effects to be recorded and replayed directly on the film sound track. The effects generator was no longer required. The 25 Hz and 35 Hz sub-audible control tones were still used to control the low frequency effects, although their specific functions were different from the Model 1 version.

I think, based on the above, that this set of alignment films must date from the release of "Earthquake" - with the Model 1 effects system. At this point, a closer look at the optical tracks seems like a good idea.

All of the Sensurround films were screened here in Melbourne. "Earthquake" had its first release at the "Palladium" where I experienced it. At the time the Cinemeccanica projectors were equipped for magnetic sound, so I'm happy enough to guess that the 35mm Mag/Optical version was screened there.

Quintaphonic sound was certainly worth considering - "Tommy" was screened here in that format. As far as I know it did not use any control tones - the magnetic sound tracks and DBX noise reduction provided sufficient range and volume. However, as always I'm happy to be corrected,

So much more to discover.
Happy Days.

[Mark Gulbrandsen]

What was the name of the color based optical sound system. I think it was 4 channel. I remember seeing one in one of the racks when the downstairs booth was used at the Chinese Theater in Hollywood. But that was the only one of those I ever encountered. I have lots of photos of the booth, but I didn't get any close ups of that processor...

[Phillip Grace]

Mark, I think that would have been "Colortek" later morphed into "Kintek" using a different technology. I remember seeing a Journal article titled "Colortek becomes Kintek" or similar.

[Sam Chavez]

I installed a number of Sensuround systems and revised them for each new release. Last one I worked on was "Battle Star Galactica". I had a few systems break out in full oscillation when the main rocket went off. Got a field bulletin from Universal and RCA, stating, "it has been found in certain instances" Actually, most of the systems in my area had the issue. I had a busy weekend modifying the settings.

[Mark Gulbrandsen]

Mark, I think that would have been "Colortek" later morphed into "Kintek" using a different technology. I remember seeing a Journal article titled "Colortek becomes Kintek" or similar.

Yes, that's the name!! And I think Kintek built those processors. It's amazing they even worked at all considering they were Kintek.

[Mark Gulbrandsen]

I installed a number of Sensuround systems and revised them for each new release. Last one I worked on was "Battle Star Galactica". I had a few systems break out in full oscillation when the main rocket went off. Got a field bulletin from Universal and RCA, stating, "it has been found in certain instances" Actually, most of the systems in my area had the issue. I had a busy weekend modifying the settings.

I got a Sensurround system from Bob a number of years back. Never could get it working, so it is probable that it was not modified for Midway, which is the film I had. I can't imagine that full system oscillation. Yikes...