Film-Tech Forum ARCHIVE: SDDS / SRD reliability

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Posted by John Walsh (Member # 168) on 06-02-2001, 06:48 PM:

I was talking to our district manager today, and he says our company is starting to see a lot of higher failures rates on SDDS and SRD prints. He thinks it's because the emulsion is getting scraped off by the trap rails, etc. That is why (he says) he is beginning to perfer DTS.

My first thought was that "someone's not cleaning that hard junk the builds up on the trap runners (most of our projectors are Simplexes.)

But he swears that is not the case; they are cleaned fairly regularly. He's pretty good at checking this; he goes right into the booth and looks at the projectors. So while he's not sure what causes the high error rate, the projectors are being kept clean.

Does anyone else have any general thoughts about this?

Posted by Joe Redifer (Member # 3) on 06-02-2001, 07:09 PM:

Perhaps an old lamp/LED in the Dolby Digital reader? It could also be slightly misaligned. But my guess is that the LED is starting to get dim.

As far as SDDS is concerned, I think you have to replace the LEDs once a year. Not quite sure on that. SDDS is notorious for cutting in and out.

Posted by Ken Jacquart (Member # 369) on 06-02-2001, 11:56 PM:

John,

Joe is right, you should check your Dolby Digital Reader's LED video amplitude. It may be low and causing drop-outs (below 2.0V as measured on an oscilloscope at the video test points... Cat 670 card). I would recommend checking this once a year, or whenever there is a suspected problem. The video amplitude is set for 4.0 volts at the factory. If the video amplitude checks out okay, then verify the other alignment paramaters... focus, lateral and azimuth.

Good Luck,
ken

Posted by John Walsh (Member # 168) on 06-03-2001, 12:39 AM:

OK, but remember, I'm not thinking of a few units. This problem of high error rates are a general impression of well over 100 SDDS and (mostly) SR-D units.

Of course, I wish I had some hard data to support this "impression" the district manager has regarding the units. Is there any was for a DA20 to internally log the degradation? We don't have enough PC's to leave connected to all the units to monitor!

I'm not sure how many lamp vs. LED Dolby readers we have, or even how many are basement readers. Do the LED readers stay in alignment longer than the older regular lamp type? Do you think that the (regular lamp type) should be changed more often than the manual recommends? Are basement readers still considered less reliable than the Cat 700 type?

Does SDDS really suggest changing LED once a year? The LEDs only come on (full) when the reader sprocket is turning. Does the manual say how many hours you can expet from the LEDs? Do they stay in alignment?

I know I'm being a bit vauge with my statement of our problem, but I guess I'm trying to see if this is fairly common. I guess I'm in the early "fact-gathering" stage to see if they fail more often then we know.

Just as an example; if we were to find out, say, that there was a high error rate at theaters that used compressed air to clean, we would have a clue whats causing the problem and ask the operator to clean differently to prevent it.

Posted by Joe Redifer (Member # 3) on 06-03-2001, 01:30 AM:

I honestly don't know what the best frquency for changing out the SDDS LEDs would be, but I was told that they would only last 2000 hours (the first units only lasted 1000 hours). Remember that SDDS uses an LED ARRAY. You can't tell just by looking at it if one LED in the array goes out or grows dim. But if one of them does, you can start seeing degradation in your digital performance.

Posted by James R. Hammonds, Jr (Member # 673) on 06-03-2001, 03:08 AM:

I just left a theatre that had 2 portable dolby digital units (that usually just stay on the big houses) that use cat 700 lamp readers.
I never once knew these to fail...the only time i remember having a dolby digital problem was with a bad reel on forces of nature (i think it was that).

SDDS was very problematic until that theatre actually got a booth manager and the LED arrays were changed and calibrted.
This was on the 200 models.
Im not sure either how long they are supposed to last because i never had to deal with them.

sony did just come out and do a reader upgrade and changed all the LEDs so well see how long they last.

The 3000 models have one LED that ive been told is never supposed to go bad.
These were put into the theatre i now work at and weve had problems with them not reading properly since opening day.
Also, the analog these new SDDS units produce has never been satisfactoy in my opinion.

If it were up to me, the theatre would not have any sdds and i would go with either dolby digital or dts for my sound system.

Posted by John Walsh (Member # 168) on 06-03-2001, 10:14 AM:

James wrote: "...i would go with either dolby digital or dts for my sound system."

Actually, that's what started this. I asked the DM why we don't just buy all SR-D. (It's not that I don't like DTS, I'm just thinking of easier maintaince; and while some films do not come out in DTS, almost everyone uses SR-D.)

Dispite the doom and gloom economy, we are not only still building theaters, but are going back to older analog screens and installing digital.

Posted by Nic Margherio (Member # 273) on 06-03-2001, 12:24 PM:

The SDDS 2000 model reader LED's can also be checked for proper voltage using an oscilliscope, and the CCD gain can be increased throughout the life of the LED's to compensate for dimming. It's not reccomended to simply change the LED's arbitrarily without checking CCD gain and flatness first. Call SCPC for the tech note regarding this adjustment, they can fax it to you right away.

James, I disagree with you about the DFP-3000. I have found the new reader to be far more reliable than the 2000's. If you are having problems with digital tracking, try running the R3000 auto-align program from a laptop computer. This tech note is also available from SCPC. Perhaps the equipment installers did not do this at installation and the readers are a little bit out of alignment from shipment? Just a guess, but is definately worthwhile to give it a try.

Also, I have found the analog portion of the DFP-3000 to be quite good, almost as good as the comparable Dolby processor, the CP500.

Posted by Ken Jacquart (Member # 369) on 06-03-2001, 12:30 PM:

John wrote, "Do the LED readers stay in alignment longer than the older regular lamp type? Do you think that the (regular lamp type) should be changed more often than the manual recommends? Are basement readers still considered less reliable than the Cat 700 type?"

I wouldn't say that the LED readers stay in alginment any longer than the older style halogen lamp readers. Be aware that although the hologen bulbs seem never to burn out, they absolutely will develop a permanent haze on their reflector which can severely reduce video amplitude. I recommend changing the halogen lamp when it fogs, or perhaps once a year (okay, you can maybe get two years before you notice any fogging). Basement readers can be just as reliable as penthouse readers depending on projector and use (or abuse).

ken

Posted by Gordon McLeod (Member # 33) on 06-03-2001, 12:31 PM:

Nic wrote"Also, I have found the analog portion of the DFP-3000 to be quite good, almost as good as the comparable Dolby processor,the CP500."
That I will disagree with I find there SR emulation very harsh and I alway have felt there EQ to be rather brittle sounding.
As far as I am conscerned the best thing SDDS could do is bring out a equivelent of a DA20 that has just the 8 analogue outputs and leave the rest to the cinema's processor

Posted by Brad Miller (Member # 2) on 06-03-2001, 01:33 PM:

The SDDS instruction sheet is in the manual download section under field bulletins, but does require an oscilloscope to adjust. It can be a bit finicky to get tweeked just right, but once it is the reader shouldn't give any problems for at least 6 months.

The internal eq in those units is too harsh and digitized sounding for my taste anyway and I have taken to bypassing it and utilizing the eq circuitry in the Dolby processor, which just wastes money on that part of the SDDS player that is no longer being used. However I have obtained magnificent results when wired in this manner. Why the need to offer internal eq in the first place is beyond me.

If you've got a cat700 SRD penthouse, be sure and check that power supply/molex connector. I've had a couple that would damage the lamp after a month or so running.

Posted by Aaron Sisemore (Member # 145) on 06-03-2001, 03:37 PM:

I believe there was a Dolby field service bulletin re: cat 700 molex connectors and the fix is to cut the thing off and wire-wrap the leads to the posts, provided the PC board has not become a crispy critter yet- then you have to go directly to the board or the alternate set of terminals if they are still OK. Same for the DA20 power supply cable, ,the molex is a weak point.

Aaron

Posted by Steve Guttag (Member # 268) on 06-04-2001, 12:46 AM:

SDDS' equivalent to the DA-20 is the DFP-D2500. It uses the 3000 series reader but is only an attachment, like the 2000 was. Also, for you changeover houses, it has two input streams unlike the previous SDDS and Dolby Digital where there is merely one that is switched.

So far, the only SR emulation that I have found pleasing is the Dolby CP-650...none of the other analog (including Dolby's CAT222SR/A) nor digital attempts sound good to me...very harsh and non natural. So far, the CP650 has been a pleasing sounding processor for both digital and analog....I was pleasently surprised.

I have not found the SDDS processors to have the brittleness described but I have found that the SDDS pink noise as generated in the 2000 to have an HF roll off as compared to either the Cat. 85 or CE SG-1 pink noise generators...as such if the same person tunes both the SDDS and another processor, the SDDS will sound more strident.

Steve

------------------
"Old projectionists never die, they just changeover!"

Posted by Joe Redifer (Member # 3) on 06-04-2001, 01:11 AM:

Maybe I'm just a moron, but why would Dolby "emulate" SR in the CP-650? Couldn't they just use the real thing since they were the ones that came up with it?

Posted by Bobby Henderson (Member # 840) on 06-04-2001, 05:22 PM:

Isn't the reason why Dolby is "emulating" SR with the CP-650 because the optical A and SR type tracks are handled in the digital realm? You don't have the same, authentic SR cards like what are found in CP-65 and CP-500 processors. I haven't heard a CP-650 in action yet, but I have read some negative criticism about it (particularly with how it handles analog tracks) on the Usenet in rec.arts.movies.tech.

On the subject of reliabilty, easy maintenance, installation and all that other good stuff, I don't see how DTS can be beat. Changing out LEDs every year? I thought a decent LED was supposed to have at least 10,000 hours of good life.

Posted by Joe Redifer (Member # 3) on 06-04-2001, 07:54 PM:

Never use digital to do analog work.

Too many people are wooed by the word "digital" these days. Just because it's digital doesn't mean it's good.

Posted by John Walsh (Member # 168) on 06-04-2001, 09:40 PM:

Like it or not, everything is being run by computer today. So much of a CP500 was digital, it's no wonder Dolby decided (with the CP650) to just go the extra step with a digital signal processor and make everything digital. If you want to change the way the emulating is being done, you can now just download new DSP code. I think SDDS has always done it this way.

While the CP650's digital emulation of SR may not be exactly the same as a regular analog SR card, it's sort of a moot point, because digital is being pushed. I would guess very few people are going to buy a CP650 and not use it with a digital sound source. So, the SR emulation will be rarely used.

Posted by Randy Stankey (Member # 64) on 06-04-2001, 09:51 PM:

I still have to agree with Joe on this one.

When emulating an analogue signal with a digital system you inevitably run into the "squaring the circle" problem. No matter how good your D/A or A/D converters you will only be able to come CLOSE to replicating the original analogue signal.

Of course there may come a time when digital systems can come closer to replicating an analogue signal than the technology we have today. As much as I like computers and junk like that I have to draw the line at using technology just for technlolgy's sake. There's just too much of that going on today and I think it's detrimantal to quality.

Posted by James R. Hammonds, Jr (Member # 673) on 06-04-2001, 09:59 PM:

<<As much as I like computers and junk like that I have to draw the line at using technology just for technlolgy's sake. There's just too much of that going on today and I think it's detrimantal to quality.>>

kind of like shooting movies on DV and releasing them on film because its a "cool" new way to make "films" and cause its cheaper.

DV movies look terrible when transferred to film, and these people still insist on calling themselves "filmmakers"

Posted by Ken Jacquart (Member # 369) on 06-04-2001, 11:25 PM:

"Squaring the Circle" will not happen if one obeys the Nyquist Theorem (along with other things). The analog wave form will be reproduced... exactly. Digital audio, when done right, kicks ass.

ken

Posted by Randy Stankey (Member # 64) on 06-05-2001, 12:16 AM:

I have not heard of the Nyquist Theorem.

I took Algebra I and Algebra II in High School but instead of taking Trig. and Calc. I took Geometry. After that, in college i took a couple of elementary Statistics classes. Is this something I would have learned if I had taken the other track? Or, is this something completely different?

Clue me in!

PS: I like digital Video but I think it should be kept in the realm of the computer screen and the internet, NOT on the big screen. LIke I said, technology is cool but you have to know where to draw the line.

Posted by James R. Hammonds, Jr (Member # 673) on 06-05-2001, 12:57 AM:

Yeah, I have no problem with digital video if thats the best your budget allows, but to use it just to cut costs is plain rediculous. The bad part is that there are people who think it will be as good as film, but in reality, they might not have seen a DV movie transfered to film yet sine this has mainly been limited to the art houses and film festivals. I dont know of any big releases that have used digital video except SPY KIDS.

I know a guy who i graduated from college with who made a pretty good quality 5 part movie (15 minutes each since it was run as a television series for our school's cable station). Our school uses mini DV cameras which produce really good video images on a TV screen, and based on this, cost, and efficiency, he said that when he starts making big movies he goig to use all digital.

I was pleased, however, that at our annual leadership conference that two different people in two different meetings said "if you can shoot film, shoot film."
At least someone in the video/film industry knows film isbetter besides just us.

Posted by Joe Redifer (Member # 3) on 06-05-2001, 02:03 AM:

I shoot in DV and I'm sure I would be horrified to see any of my creations transferred to film.

Ken is right. Digital audio kicks ass. Most of the time. I don't really care for the digital EQing scheme in the latest processors from Sony and Dolby. There is just no way that you can achieve the same exact curve with digital EQ as with an analog EQ each and every single time. But that's a different story.

The point I am trying to make is that people automatically associate the word "digital" with "the best it can possibly be". Have you seen ads for the latest TV hard disc recorders, etc? They advertise that they record up to 4 billion hours (or so) in "full digital quality". Well, since it's digital it must kick the living hell out of VHS! Nope. When you see the 4 billion hour low quality mode it's not even as good as Video CD. And Video CD is noticably worse than VHS (even worse than VHS in EP if you ask me, just due to the artifacting). MPEG sucks (MPEG 2 is better, but I can still see lots of artifacts on DVDs, especially in dark scenes). But its digital, right? So no matter how bad it is, it's still waaaay better than any analog recording device!

"Digital" and "Digital Done Right" are two completely different things! Don't fall for a cinema processor just 'cause it says "digital processing" in the ads. That doesn't mean it will sound good. Audition it for yourself first!

Posted by Scott Norwood (Member # 30) on 06-05-2001, 06:39 AM:

I personally have a pretty low opinion of DV as a video format, even for television use. To me, it looks _substantially_ worse than Betacam SP (a 14-year-old analog format) because of the compression artifacts and other problems.

I agree that it's better than any other home format currently available and that the equipment is far cheaper than the Betacam gear, but neither comment is saying very much, unfortunately.

(I once looked into the cost of renting Betacam equipment. It turned out to be cheaper to shoot and edit 16mm film for the short that I was working on...)

Posted by Tao Yue (Member # 836) on 06-05-2001, 07:54 AM:

The Nyquist Theorem is not generally taught in high school mathematics courses. It's usually taught in Electrical Engineering courses, and applies to digital sampling of audio. The theorem states that to accurately represent a continuous analog waveform using discrete samples, the rate of sampling must be twice the component frequency. For example, standard CD audio is sampled at 44.1 KHz, meaning that no sounds greater than 22.05 KHz are recorded. This is actually not caused by the sampling itself -- frequencies greater than 22.05 KHz would simply get distorted beyond recognition. (See http://www.opus1.com/~violist/help/nyquist.html for an example of what happens to a signal above half the sampling frequency.) The Nyquist Theorem is applied by using a low-pass filter to remove all frequencies above that threshold.

However, it is not true, as Ken stated, that the waveform will be reproduced exactly. Take a sine wave sampled at exactly twice its frequency. Try it yourself -- instead of a curvy sine wave, you'll get a triangle wave. At 22.05 KHz, you'd be hard-pressed to notice the difference. Hook up a function generator to a set of headphones and compare low-frequency sine and triangle waves, though, and you'll notice a distinct difference.

The Nyquist Theorem ensures an accurate epresentation of the signal, but "squaring the circle" (or in this case, triangling the sine) always occurs when trying to represent a continuous input discretely.

--
Tao Yue
MIT '04 Course 6-2: Electrical Engineering and Computer Science
Projectionist, MIT Lecture Series Committee

Posted by John Pytlak (Member # 331) on 06-05-2001, 10:02 AM:

With digital imaging systems, a low pass filter is sometimes necessary to reduce "aliasing". In effect, if the system is allowed to be too sharp, it could be prone to annoying moire patterns. You can often see this problem in digital video when you have moire in finely-detailed patterned fabrics, picket fences, venetian blinds, screen doors, etc. For examples, see the thread where Evans Criswell discusses sampling frequency and aliasing.

Any digital camera or projection system that uses a fixed array of pixels may suffer aliasing unless a low-pass filter or defocusing are used to minimize the risk of interference.

Here are some links:
http://www.kodak.com/US/en/digital/dlc/
http://www.spie.org/web/meetings/programs/or97/sc/or97_sc22.html
http://www.imagingspectrum.com/portraitcomparison.htm
http://www.kodak.com/cluster/global/en/service/faqs/faq1082.shtml

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Mark Gulbrandsen (Member # 72) on 06-05-2001, 11:51 AM:

Steve Guttag said in an earlier posting.....
"So far, the only SR emulation that I have found pleasing is the Dolby CP-650...none of the other analog (including Dolby's CAT222SR/A) nor digital attempts sound good to me...very harsh and non natural. So far, the CP650 has been a pleasing sounding processor for both digital and analog....I was pleasently surprised."

Steve,
Give a listen to the Panastereo Processor with the new SR card. You'll be very surprised at how much better it sounds!

Joe said
"Too many people are wooed by the word "digital" these days. Just because it's digital doesn't mean it's good.

Joe, you hit the nail on the head!
Take the Panastero Processor for instance. Blows em all out of the water by a long shot.

IMHO, Dolby should have and could have lowered the price of the CP650 substantially as it is far cheaper to mass produce than the 500 was.
Mark @ GTS

Posted by Ken Jacquart (Member # 369) on 06-06-2001, 12:30 PM:

Tao,

A properly designed A/D and D/A conversion process does not simply sample a waveform, and then reconstruct the samples by ordinary linear interpolation (connect the dots). This would require a tremendously high sample rate to adequately reproduce the input signal. There are 'other things' that go along with following Nyquists theorem to stay out of trouble. One of those things is to low pass the input signal at the half-sampling frequency. This is also know as an anti-aliasing filter. Another one of 'those things' is to provide an (ideal) low pass reconstruction filter at the output, also known as a smoothing filter. This filter will have a sin(x)/x impulse response. When samples of the bandlimited input signal (remember the low pass filter at the input?) are processed with this impulse response, the input signal will be exactly reproduced...there's more too...

ken

Posted by John Pytlak (Member # 331) on 06-06-2001, 12:45 PM:

Ken --- the same EE communication theory that applies to digital images also applies to digital sound (e.g., low pass filters to reduce aliasing, Nyquist theorem, etc.).

Posted by Bill Langfield (Member # 818) on 06-06-2001, 01:13 PM:

Mark. yup, Nothing wrong with Panalogic.

SDR is here to stay. So Dolby will rule.
even ads are srd these days (even with the bad error rates)
I prefer DTS as it has less drop outs.

Bill.

Posted by Tao Yue (Member # 836) on 06-06-2001, 01:50 PM:

You're absolutely right, Ken. I should not have said that "a waveform cannot possibly be reproduced exactly" (paraphrase of the impression that my earlier post erroneously gave), but rather "a waveform will not always be reproduced exactly." I gave linear interpolation of a sine wave as an example of a way in which digital audio can fail. I'm sure someone else can come up with a better example. The Nyquist Theorem states that no information will be lost if the sampling rate is twice the maximum frequency, but it doesn't say that you can actually do it. This is mathematical perfection, which doesn't exist in the real world.

When you change from one form to another -- analog to digital, English to French -- you lose something. But, as you mentioned, there are "other things" that you can do to get closer to perfection. Is there an ideal low-pass filter? No. Is there something that's damn close? Yes. Likewise with the sinc filter.

I still maintain that analog to digital and back will never be perfect because you're always trying to square a circle. The limit of this operation as our technical knowledge grows is a perfect square, but we'll never get to it. Eventually, though, we'll reach a point where the A-to-D conversion will surpass our ears' abilities to discern imperfections. And in that sense, I agree with you that digital audio can be "perfect" (to us).

Posted by Tao Yue (Member # 836) on 06-06-2001, 02:14 PM:

For those of you interested in the discussion of communications theory and its impact on digital representations of analog data, go to the following site:
http://www.siglab.ece.umr.edu/ee301/dsp/adda/ada.html

It has an excellent discussion of the Nyquist Theorem, aliasing, and interpolation methods, complete with graphs.

Posted by John Pytlak (Member # 331) on 06-06-2001, 03:18 PM:

Tao: Thanks for the link. The other items in that "Real Time Signal Processing" Course are also very good:
EE301: Real Time Signal Processing
Digital Signal Processing

People like you and Evans Criswell bring back memories of my EE courses. Been there, done that (but not doing it right now).

This great stuff is the foundation of digital imaging and digital sound. Lots of challenges to "Do Digital Right".