Dolby Stereo "A" Screening Issue

[Ryan Gallagher]

We just had a slew of the less common these days Stereo (Type A) optical prints come through our booth. On one print last night ("Friday" 1995), our programmer who typically sits at the back of the house pointed out an oddity. There was what sounded like a full mix including dialog coming through the surrounds (or rears that we noticed, but probably all of them), albeit at a lower level compared to the main center channel dialog. You could watch a dialog only scene on the AP20/CP650 meters, and observe that indeed all channels were activated with dialog, but at relative levels. I did step out of the booth long enough to confirm his ears were not lying to him!

Format 04 (Stereo A) on our CP650 could certainly be investigated. As well as format 650 on our AP20. But the impression was that the very next StereoA print that night sounded fine/normal...

What could be at play here? I'm aware of the nuances between SR and A, and they are both 4 track decoded formats. Was maybe the "Friday" print only containing 2 channels of information and the 650 was set to do some magic with the rest of the auditorium channels that maybe it shouldn't be doing?

Can A-Chain issues create the effect that was being heard as well?

It's probably been eons since an actual tech did any A-Chain or B-Chain work to the analog side of our booth, probably 2016 when the DCI system was integrated. I've been to hoping to check all those things but it's been lower on the priority list till now, since everything was just working as expected. Maybe our Stereo-A 650 format is mis-configured to play nice on all films and has been so for decades?

The final option is that it was a very cheaply made LtRt 4 track upmix originally, and it's just in the mix that way, but I kinda doubt that. Not having done much poking at the 650 settings yet I did not fire up 650 Setup tools while a film was running, unsure if it would interrupt anything if I found an edit to make and push the config.

[Brad Miller]

Friday was printed on acetate stock. All acetate stock shrinks over time to varying degrees. That shrinkage can cause the optical reader to effectively not be properly aligned with the track on the film. Pure equal mono sounds (dialog) are routed to the center channel so when the alignment is off, it will skew the dialog into the left/right and most obviously the surrounds.

I'll bet the title you ran after that was on polyester stock (which doesn't shrink) or was on acetate stock that did not have the same degree of shrinkage as the Friday print.

Keep in mind also Dolby A vs SR has nothing to do with the steering of the audio which is your complaint here. However by the time SR prints became the norm, polyester was becoming the norm so it's easy to see how this might be inaccurately blamed on the track (or processor) using "A" noise reduction.

[Ryan Gallagher]

Taking note of the fortuitously timed A-Chain alignment discussion here and mentions of SR bleed as a possible artifact, other than confirming everything looks normal on the 650 04 format, I think optical alignment is my next most likely culprit. Just curious why it was so pronounced on one print but not the other.

(composed before Brad's response)

[Ryan Gallagher]

Friday was printed on acetate stock. All acetate stock shrinks over time to varying degrees. That shrinkage can cause the optical reader to effectively not be properly aligned with the track on the film. Pure equal mono sounds (dialog) are routed to the center channel so when the alignment is off, it will skew the dialog into the left/right and most obviously the surrounds.

I'll bet the title you ran after that was on polyester stock (which doesn't shrink) or was on acetate stock that did not have the same degree of shrinkage as the Friday print.

Keep in mind also Dolby A vs SR has nothing to do with the steering of the audio which is your complaint here. However by the time SR prints became the norm, polyester was becoming the norm so it's easy to see how this might be inaccurately blamed on the track (or processor) using "A" noise reduction.

Thanks Brad, Yes your statements about the base are correct from memory. Acetate for Friday, and Poly for House Party (a reprint I think, didn't have the full countdown visible... kinda faded into existence). So it might have just been shrinkage and we are fine.

A-Chain alignments is certainly worth checking, but I'm less inclined to assume something is actually wrong there going into it now that you have pointed out the shrinkage factor.

[Ryan Gallagher]

As an amusing related aside on A-Type tribulations for relative newbies, if anyone plays the Ladyhawke print we had recently... it's now labeled Stereo A Type clearly on the reels. Ever since I became aware of how difficult it is to tell sometimes I wondered when it was going to bite us, Ladyhawke was that occurrence. We didn't have the SR roll-out year burned into memory yet, and that film fell right on the cusp. Production was the year before, but released same year as SR came into existence.

(Granted A type stayed around for much longer that that)

It didn't help that we had a guest/relief projectionist for that one, and I had been running loops in SR format prior. It was caught mid screening (though not as early as one would like), and switched at a changeover.

Learning things the hard way, now we have that date in our collective memory, as well as knowing to always check the tag in credits (though not 100% reliable) and any internet sources you can muster (also not 100% reliable). If all else fails and still not sure, simply have to do an auditorium listening test for those tell tale dynamic range and distortion issues. To be fair the lab leader did just say "Stereo" on it, but inexperience led to that not causing the "ah ha", as you often see "Stereo-A" there after SR came into existence.

Cheat code, if it sounds like you have to turn the fader way up for the quiet dialog scenes, but the loud non-dialog stuff is cranking, you might be in the wrong optical format.

[Steve Guttag]

The rule of thumb was that 35mm optical that was released before 1993 are almost always Dolby-A. They were not labeled as Dolby-A since Dolby-A was all there was for professionals. While Dolby-SR existed in the mid/late '80s, it did not take hold in theatres until Dolby Digital forced the issue. Orion Pictures was an early adopter of Dolby-SR on 35mm optical. So, if you have a late 80s Orion film, then I would pay closer attention to the noise reduction.

70mm magnetic was a bit more smeared on when it was adopted. Select titles played with it. From personal experience, from about 1989 onwards, most, if not all of the 70mm prints I handled were Dolby SR. The turning point seemed to be Lawrence of Arabia restoration.

[Ryan Gallagher]

Thanks Steve for the wealth of history and knowledge. It’s also better to be wrong in the other direction. A better boot practice in a rep house now would be to default to A-Type and only upgrade screening to SR when the evidence supports that interpretation during inspection/research. SR was after all “supposed” to be somewhat backwards compatible to older processors, though playing it as SR would be the goal.

[Michael Coate]

Ladyhawke was that occurrence. We didn't have the SR roll-out year burned into memory yet, and that film fell right on the cusp. Production was the year before, but released same year as SR came into existence.

”Ladyhawke” should not have caused any confusion since it was released over two years before SR (on 35mm) was introduced. “Ladyhawke” was released in April 1985, whereas Dolby SR (on 35mm) was introduced (on some prints of “Innerspace” and “RoboCop”) during July 1987. (“Star Trek IV” had SR prints—which explains why some sources cite 1986 as SR’s year of introduction—but the SR was only on a couple of its 70mm Six-Track mag prints and not on any of its 35mm prints.)

Tech trends historically take time to gain traction and so even citing 1987 is misleading as SR didn’t become common until some time later.

[Steve Guttag]

The cutsheet for the Dolby SRA5 (SR adapter for the CP50, 55, 100 and 200) is from 1988. Dolby wouldn't have brought it out unless there was an anticipation of demand...that and the CP55 was sort of stuck. The CP50, 100 and 200 could just card swap Cat 22s for CAT280Ts...the CP55 with the CAT222 couldn't do that. I do maintain, until Dolby Digital forced the issue, Dolby-SR on optical 35mm didn't go widespread. It was on select titles and not single inventory.

There was a company called "Audio Rents" where one could rent CAT280Ts for the duration of the run of a title (35mm optical or 70mm magnetic) to avoid the expense of buying SR for the rare-bird event.

[Tony Bandiera Jr]

The cutsheet for the Dolby SRA5 (SR adapter for the CP50, 55, 100 and 200) is from 1988. Dolby wouldn't have brought it out unless there was an anticipation of demand...that and the CP55 was sort of stuck. The CP50, 100 and 200 could just card swap Cat 22s for CAT280Ts...the CP55 with the CAT222 couldn't do that. I do maintain, until Dolby Digital forced the issue, Dolby-SR on optical 35mm didn't go widespread. It was on select titles and not single inventory.

There was a company called "Audio Rents" where one could rent CAT280Ts for the duration of the run of a title (35mm optical or 70mm magnetic) to avoid the expense of buying SR for the rare-bird event.

I remember them!! Many theatres in my service kit (As RCA liked to call them) had those rented cards installed. Those who rented them right before Audio Rents went under got lucky and kept them as there was no one to return them to.

I also recall buying a CP 200 that had those rental cards in them.

[Tony Bandiera Jr]

It's probably been eons since an actual tech did any A-Chain or B-Chain work to the analog side of our booth, probably 2016 when the DCI system was integrated. I've been to hoping to check all those things but it's been lower on the priority list till now, since everything was just working as expected. Maybe our Stereo-A 650 format is mis-configured to play nice on all films and has been so for decades?

That is WAAAY too long, especially at a venue like yours where you run film regularly! A venue like yours should never go more than a year (if you have old school standard readers with exciter lamps) or two at the very most (with newer LED based reverse scan readers) between A chain alignments. And if your readers of either type are powered up all of the time, no more than 3 or 6 months, respectively.


You need to get a technician in ASAP with all of the proper test films and equipment to do a full alignment. (Make sure that tech does the illumination uniformity test too.) Be ready to replace exciters or LEDS.

Once that call is done, you should only need to run a Dolby Tone loop (and Buzz Track) monthly to keep things tuned up. (That will account for reader light source aging and mechanical wear on your lateral guides.)

You (and your management) will be shocked at the improvement in sound quality by this one simple service call.

In all my years servicing hundreds of theatres and home screening rooms, I had never found a single one that wasn't out of alignment if left alone for more than six months to a year. The ones I did quarterly maintenance on would only be very slightly off, unless something got damaged or messed with.

I did not fire up 650 Setup tools while a film was running, unsure if it would interrupt anything

NEVER mess with ANY of the CP650's menu options with a film running!! It WILL most definitely interrupt the film sound and some options will reboot the processor. That is one reason why many techs set a non default password to the setup menus.

[Chris Wehrman]

Are replacement LEDs still available, such as for the kelmar reverse scan analog readers? I'd like to purchase one of one could be had somewhere.

[Ryan Gallagher]

Replacement LEDs are on our list too, I need to verify which model. Dolby diodes were replaced, and we do run tone and it is still able to auto cal, but we are at our trim limit on one of the readers, so that issue is coming to a head soon!

You don’t have to tell me this stuff is overdue, convincing management when optical is only 5% of what we run is the real challenge. If anyone knows a central Texas tech other than Brad I’d be happy to put in a recommendation.

[Ryan Gallagher]

That is part of why I’ve collected the needed loops and tools etc myself, fully expecting to have to find time to teach myself A-Chain reverse scan alignment “soon”.

[Jim Cassedy]

Assuming you've got an original 'vintage' print, with the leaders intact, the format type was
often printed in the soundtrack negative area. (STEREO or SR, etc) Also if it's DOLBY, I'll
look at the Dolby bug in the credit roll. Dolby changed the wording over the years.
(Presented in Dolby Stereo, (in selected theaters) or DOLBY SPECTRAL RECORDING
, which was sometimes spelled out, or shortened to Dolby SR) Dolby used to have a page
on their website with their sound format logo evolution, but I haven't looked in a long time.

Example Of A Track ID-
UltraStereo_Trk.jpg
(also known as "Format U")

>Speaking of sound stuff, it was 96 years ago this week, on July 18 1929, that
my venue installed it's first 'talkie' sound system. According to press releases
at the time, it was "the largest RCA Photophone installation West of the Mississippi"
> They fired their orchestra within the next 3 months. During some recent work in
our basement, I discovered the old entrance to the orchestra pit, which had been
hidden behind a lot of old theaterstuff.

> The 1929 sound system was replaced by an equally large and updated Photophone
system during a major remodeling around 1939/40-ish