Film-Tech Forum ARCHIVE: Help! no sound from cyan track with Kelmar IR reverse scan

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Posted by Steven J Hart (Member # 2340) on 05-28-2005, 10:14 AM:

I opened Madagascar last night and had no sound when the feature started. The attached cyan track trailer played fine (through DTS) but the processor switched back to analog when the feature started. Upon manually switching back to DTS, the feature played fine. I had the same problem last week with The Hitch Hikers Guide to the Galaxy.

Lets back up a bit. I've got a Century R5 sound head fitted with an eight year old Kelmar IR reverse scan reader. The output from the reader feeds an Ultra Stereo processor. As mentioned above I've got a DTS 6D (Thank God). I've heard that if you try to read a cyan track with white light you get sound, but at a reduced level. I've never heard of having no output at all from a cyan track using IR light. The Ultra Stereo preamp board has level meters for calibration purposes. While the feature played last night these meters showed no output at all! My pre-show policy header uses a standard magenta track, and this plays back fine.

It boils down to two questions:
Were some of the early model Kelmar readers not compatible with cyan, or is mine malfunctioning?

Why would my DTS unit switch the Ultra Stereo back to analog when the feature starts?

Posted by Mark Gulbrandsen (Member # 72) on 05-28-2005, 10:48 AM:

quote: Steven J Hart
Why would my DTS unit switch the Ultra Stereo back to analog when the feature starts?

Perhaps a reader needing adjustment of the 4 volt preamp level, a bad reader, bad DTS track, or bad disks.... I have not had any specific problems with the film out this way. This is generally why most operators pre-run a film before hand, assuming enough time to do so.

You just need to have your tech come in and change the IR led over to red. The IR led is not compatable with the cyan tracks. Also make darn sure that the new red led is running at a reasonable current draw, some of the early Kelmar power supplies need to be modified to ensure this.

Mark

Posted by Steven J Hart (Member # 2340) on 05-28-2005, 11:42 AM:

Thanks for the solution, Mark. Any idea why the sound format doesn't want to switch to Digital when the feature starts?
Steve

Posted by Darryl Spicer (Member # 711) on 05-28-2005, 05:38 PM:

Because there is a section of film between the last traler and feature that has no DTS timecode and for some reason your dts will not pulse back to digital.

Posted by Dominic Espinosa (Member # 2122) on 05-29-2005, 04:24 AM:

Just my 2 cents but relying solely on DTS or any digital format for that matter isn't a very good idea. You should really look into upgrading to red LED readers.

I've had about enough of DTS soundtracks, thanks to episode 3.

Posted by Frank Angel (Member # 248) on 05-29-2005, 07:36 AM:

quote: Dominic Espinosa
Just my 2 cents but relying solely on DTS or any digital format for that matter isn't a very good idea.

Right you are....and doesn't that say something about the reliability of digital sound? You would think after all this time of it being in use, the bugs would be worked out completely, or at least enough for it to be as reliable as analog. I mean, imagine if when sound-on-film system was put into place, if ten years into its use, they still needed to keep the disk soundtrack running in case the optical track failed. So when will we get to a point where the digital track will need no analog backup, apart from needing it to play the few analog-only tracks on snipes and stuff?

Posted by Bill Enos (Member # 440) on 05-29-2005, 08:10 AM:

Nothing digital is more than moderately reliable under the best of conditions, even the best booth is no computer lab.

Posted by Dominic Espinosa (Member # 2122) on 05-29-2005, 09:29 AM:

quote: Bill Enos
Nothing digital is more than moderately reliable under the best of conditions, even the best booth is no computer lab.

That is one of the biggest problems.
Anything digital requires much more tuning than it's analog counterpart.
And the locations of the digital tracks excluding the DTS timecode make them more susceptable to damage in poorly aligned and maintained film paths.
Incidentally the only problem I've EVER had with SDDS is when our processor's APR board had some faulty components causing noise in some chanells.
But a processor malfunction can't really be a negative against the format unless it's an issue that plagues it.

Moreover, in the event of a lab defect or other printing issue another digital format would have to be available and it seems to me that it's much more expensive than to keep analog around.
And since a lot of venues exist who will play film without a digital soundtrack (low budget, some previews, etc) it just makes sence to keep the optical as the backup.
If it's done right Dolby SR can sound very very good.
Most audiences can't tell the difference, not to say you should try and get away with saying it's just as good sounding as digital, but it's a completely passable backup.

Posted by Scott Norwood (Member # 30) on 05-29-2005, 10:16 AM:

The problem with digital is the failure mode. Few theatres have optical systems which are perfectly aligned, but the system fails gracefully and the result is acceptable unless the alignment is way off (i.e. excessive dialogue audible in the surround channel, etc.). Further, even without test films and equipment, pretty much anyone can get an optical system to reproduce sound, even if the alignment isn't perfect. By contrast, digital either works or it doesn't, and it is difficult or impossible to tell why it isn't working without test equipment.

I still say that any print with an unplayable soundtrack is defective and should be reported to the distributor as such. Unless it is a single-inventory release (which hasn't been done yet for a major title, as far as I know), he should get a silver-track replacement. If no one complains, film distributors will assume that there are no problems.

Posted by Mark Gulbrandsen (Member # 72) on 05-29-2005, 11:15 AM:

quote:
The problem with digital is the failure mode. Few theatres have optical systems which are perfectly aligned,

Scott,

Thats why I preach that the analog chain HAS to be as good as the digital chain... Those that don't think this way should not be in the buisness as it shows they really don't care about sound or their customers... many dealers fit in this don't care catagory, or are preaching that analog is just a back up....thats bull and a dealer that really doesn't care about his customer! There is still the occasional small film that turns big that is not digital and to make defaults back from digital as un-noticable as possible.

Mark

Posted by John Hawkinson (Member # 1135) on 05-29-2005, 11:24 AM:

The real reason that the digital sound we have today is not as reliable as analog sound is because it was not engineered for that level of reliability--it was engineered to do more (5.1 discrete) than the analog soundtrack, but in less physical space.
So, because SRD is in much less area than the analog track, and in a location that is easier to damage, it is not as robust. If it were blown up larger and took up more area, the SNR would be that much better and damage would be tougher.
SDDS seems to have its own special sets of problems (is it printing? Is it wear on the edges? Is it dirt migration?).

I guess you should be able to argue that DTS ought to be capable of matching the reliability of the analog track, at least where the discs are undamaged and present. I don't really have a good explanation for why that doesn't seem to be the case [ok, ok, moving parts?].

All in all, though, I don't think the wrong engineering choices were made. It's simply the case that rock-solid robustness was not a design goal for SRD and SDDS. One vaguely wonders how reliable a modern-day CDS reader might be [Smile]

--jhawk

Posted by Scott Norwood (Member # 30) on 05-29-2005, 11:25 AM:

Absolutely agreed. Most of the stuff that I've shown lately has been either smaller films or older films, neither of which usually have digital tracks. No one should install digital anything until the optical system is as good as it can be. I hate seeing crappy systems with a DTS unit thrown in the rack so that the marquee can say "DIGITAL SOUND."

Posted by Mark Gulbrandsen (Member # 72) on 05-29-2005, 04:16 PM:

quote: John Hawkinson
So, because SRD is in much less area than the analog track, and in a location that is easier to damage, it is not as robust.

Hawkeye,
Actually SRD has THE most robust(largest size)digital data of all the on film systems. The only thing SDDS has going for it and the only reason it sometimes works is the dual redundant tracks. Stand sometime through a bunch of previews and watch the two track LED's blink on and off on a 2000..... amazing that it works at all.

Posted by Steve Guttag (Member # 268) on 05-29-2005, 06:10 PM:

The problem isn't that it is digital persay but that it is going through an analog step (the film) and then must be read analog before it can be digitally decoded. As John pointed out the digital tracks are taking the "leftovers" in terms of space on the film and then being decoded with all of the printing difficulties mixed.

Digital audio is working rather well for DVDs and a slew of broadcast equipment. AES/EBU is pretty darn reliable. With metadata...the signal can identify itself and potentially ensure it is decoded properly.

How many DCinema theatres have problems with their audio being decoded right? It is discrete AES audio.

Posted by Frank Angel (Member # 248) on 05-30-2005, 02:16 AM:

quote: Steve Guttag
Digital audio is working rather well for DVDs and a slew of broadcast equipment. AES/EBU is pretty darn reliable.

It is, for the most part, Steve, but in the recording studio right upstairs from me one of the top engineers in the country has a saying....In digital, if you don't have it down three times, you don't have it at all. He always has multiple machines runnning on ever session.

And John raises a really good point....how much better than any of the current digital on film systems would the original Kodak CDS system be in terms of reliability, given that it had the entire space of the analog track. It wasn't using left-over geography -- it had plenty of uninterrupted space. Reliability might have been quite as high as analog. Anyone ever work with that system in a regular theatre situation? In theory it had to be as reliable as analog because there was no backup whatsoever. I wonder if it was, especially over splices & the like.

I think Dolby really did their homework in R&D on where to put their track. They went to something like 30 regular theatres and gave them 20 feet of black film and had it spliced into their trailer pack. They had the theatres run it for 3 months and then they took them back and inspected them for wear. They compiled the data and discovered that the least wear was exactly where they decided to put the track. In fact, they were toying with the place they first were looking at, i.e., the film edges (ala SDDS) as it seemed like a natural place to consider. But the wear patterns told them this area was very problematic. Sony attempted to compensate for the wear problems in this area by redundency on the each side, but from what we keep hearing, when prints get older, even doubling the tracks doesn't seem to be enough.

Posted by Michael Schaffer (Member # 1204) on 05-30-2005, 03:12 AM:

quote: John Hawkinson
SDDS seems to have its own special sets of problems (is it printing? Is it wear on the edges? Is it dirt migration?).

Mostly printing. A really well-printed SDDS track will last until judgment day and beyond.

Posted by Brad Miller (Member # 2) on 05-30-2005, 04:03 AM:

quote: Michael Schaffer
A really well-printed SDDS track will last until judgment day and beyond.

IF...it is properly taken care of during projection!

Posted by Matthew Jaro (Member # 1786) on 05-30-2005, 04:10 PM:

I wonder why Dolby didn't use both sides of the film for SRD? I know this would make the readers more expensive, but could that be the only reason? The current system does not have much bandwidth and relies on "masking" effects to appear to be 5.1 discrete.

There are 5776 dots (fixels)in each Dolby square The matrix is 76x76. If no dots were used for the DD sysmbol, registration, and CRC bits, then the bandwidth would be 5776 (x 4 perfs per frame) (x 24 fps) = 554,496 bits per second = 69,312 bytes per second. A standard stereo CD has 44k bytes per second per channel (to provide a point of comparison). All of this to run 6 channels with good frequency response. It's amazing it sounds as good as it does.

Posted by Dave Macaulay (Member # 813) on 05-30-2005, 10:09 PM:

It's not reasonable to compare the CD audio format with any compressed format. I think the CD audio specification was designed to waste space; they had ~700MB to use up and they couldn't allow more than 60 minutes of audio to fit into it or customers would surmise they were getting ripped off (I paid $20.00 for 45 minutes of music but I know the disc holds 12 hours worth!). A CD of 60 odd minutes of digital silence (ie every sample = zero) still takes up the whole 700MB. A lossless compression system could save it in a few bytes.
Any honest data rate comparison should be between a good lossless compression scheme and the schemes used by SRD, SDDS, and DTS. This doesn't address sound quality. I think they all sound pretty good.

Posted by Randy Stankey (Member # 64) on 05-30-2005, 11:45 PM:

I have to agree with Scott. When any kind of digital system fails, it's "All or Nothing".

With analog sound, at least, there is a continuum of failure, between the extremes of which, there is still acceptable sound.

If your theater is otherwise well-run and you have built up a good clientelle they will be tolerant of the occasional equipment failure whereby the show runs in mono or, maybe, at a lower volume level than normal. Some people will complain. Others will give you a "mulligan" because they know it's probably something really wrong that caused the malfunction. Now matter how you slice it, you can still stay open for business.

With digital, you're talking about a horse of a different color! If your sound fails you COULD find yourself dead in the water! If your analog backup is working correctly, maybe your customers wouldn't even notice. If it wasn't for that, you'd be dead in the water! Out of business untill it's fixed!

I have said it here before... And most people have Pooh-Poohed my for it but I'll take this opportunity to say it again:

When pre-screening prints it is prudent to always screen in ANALOG SOUND!

If your digital sound fails, you're going to NEED analog! If you are not an "All-Digital" theater you are going to need analog at some point. When/if that time comes you had better be able to rely on your analog soundtrack!

If that track is bad, you're going to need to replace it our be out of luck! If you replace it soon after receiving the print, the distrubutors aren't going to question you asking for a new print. If you call for a replacement 2-3 weeks out, they are going to ask questions. Further, it's just a lot more hassle!

Pre-screen in ANALOG!

If your digital stops working, you are saved.
If you move the print to a non-digital house, your ass is covered.
If the ditital soundtrack(s) is bad you can still get a replacement print on the opening weekend but, at least, you'll have a good analog track to fall back on.

I used to tell kids who screened prints that all the time but they didn't do it because they just wanted to hear the film in digital... just becasue digital is "better".
I just said, "Waaah! Waaah! Waaah! Whine! Whine! Whine! You're not here to have fun watching a movie! You're here to do a JOB!!" I used to get a lot of looks like I just knocked their ice cream cones into a mud puddle! [evil]

Even after scolding them, I'd go up to the booth and find then screening in digital. I would turn the digital processor off. They never knew the difference! I even remember one time when I got a report of "bad sound" in a screening right after I turned off the digital processor. The next day, I made that person order a new print. I told him, "If you screened that movie in digital you never would have known it was bad!"

Posted by Dominic Espinosa (Member # 2122) on 05-31-2005, 07:39 PM:

The idea of having a backup (analog) is that it should be a viable backup.
You would think it unacceptable to use a trashed floppy as your "viable backup" of an important document when your hard disk eats the big one.

A theater using SR for a backup format should have it tuned and routinely checked for proper opperation, even if they hardly use it, the audience shouldn't be able to tell the difference without looking for it.
We can, but we're supposed to be able to.

Posted by Mark Gulbrandsen (Member # 72) on 05-31-2005, 08:43 PM:

One thing that I find it hard to believe is that no one has incorporated a DC servo into the reverse scam readers yet to keep the LED bias at a constant level over its life spam I find it very amusing in this day and age that we still have to adjust and calibrate dolby levels at regular intervals. Today this should be automatic and done by the pickup itself!

Mark