P side: C L LC SL - Rm [backup] (mixed R RC SR - compressed SW)
S side: R RC SR SWC - Lm [backup] (mixed L LC SL - compressed C)

If for example the P side is damaged and unreadable, it will pull the C L LC SL from the backup contained on the S side.

This way if one side of the film is completely unreadable, is still has a backup of the channels that were on that side. The backup channels are of very high compression and lower quality taking up less bandwidth. I may be mistaken, but some of the channels may be even drived via matrix such as R + LC = C but of that I'm not sure of. Blocking 1 side of the film would only force the backup channels of the affected side. There has to be a software swith that would disable the backup tracks however Sony probalby has those locked in a deep dark corner of the coding, then again it may be hard coded that way as well.

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I found this on www.sdds.com
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"With SDDS, both edges are used to provide two continuous streams of data interleaved using a cross-redundant error correction technique to further prevent drop-outs from film damage or scratches."
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It suggests that both sides are used and that one side does not function just as a back-up.

So I am slightly confused now.

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Ok...on SDDS there is no back up side or track in the conventional sense. Both sides in are in use at all times. The only redundant channels are C and SW, that is if either track is covered up, both Center and Subwoofer will play unaffected....but what about the other channels, I hear you cry!

SDDS has what they call "Digital Concealment Mode" or DCM for short (in our current world, why use a single word when mutiple words for describing backup can be used...also the neat abbrieviation DCM)...

What has been said above is essentially true however...there is a back up track (in the singular form) located on each side...it is known as the "prime" track...a bit confusing since "prime" to theatre people nomrally means main or first choice...not so in SDDS speak. The SDDS prime tracks contain a sum. In the case of Left Prime, written as L', you have Left, Left-Center, and Left-Surround all mixed together. You then also have encoded how loud the channel should play on a channel-by-channel basis. However, with film space getting tight and bits available running low...you don't get too many bits for how loud things should be so, and this is only from memory so I may be a little off on this, there are are only 256 "steps" or levels each channel may be played. So, in theory, if the surrounds were playing at say 82dB and Left was playing at 70dB and Left-Center was playing at 0dB...then the summed L' track will play out of those channels at their respective levels within the resolution of 256 steps. If an effect was originally playing out of Left channel only, the surround channel, in this case, would actually be playing it louder than Left while in DCM (82 vs 70dB).

To try and make the system more bullet proof, the P and S tracks are out of sync with each other (17 frames comes to mind but again, I may be off on that number)

Does the system work? Yes, in limited applications...for instance, during a splice, both tracks are blocked but due to the 17 or so frame offset, each track goes into DCM separately and MOST people won't notice it. It was designed to keep the levels pretty close to actual. In fact, it is more seemless than an analog fall back.

But wait, I hear you scream, why do I keep hearing when the SDDS system spazes out (Brad's term, and accurate). Becuase the prime tracks are ok to fall back to for an instant...not to be played on or repeatedly gone to. It is like a magician that moves so slow you see the trick...it then becomes obvious something is wrong.

SDDS should have a better failure algorythm such that if one track is blocked for an extended period of time (say two frames...allows a splice) then it should release the digital system. Furthermore an algorythm should be set up to keep track of how many DCMs happen over a period of time...so lets say two DCMs over 24 frames would also go analog...then monitor the tracks and if they clear up, come back to digital. I'm not saying these are the ideal algorythms, actual listen tests would need to be done to come up with ideal times to deterimine what is noticable rather than what is not.

What SDDS hasne't figured out (at least on the 2000) is that switching to either DCM or ACM a lot is worse than staying in analog. Don't get me wrong, the DCM method has merit. Unlike Dolby or DTS when fauting to analog is almost always detectable (particularly in the surrounds), a fast and short DCM doesn't have the surrounds jump in level or start hissing at you. The real annoying thing is that this sort of problem should be fixable in software/firmware.

Brad:

I believe you said you have the DFP-2000 on your JM11/JM21 loop. If you are handy with electronics...you could monitor the "Data Present" tally on the "Automation" connector...if it is off or strobing, it has faulted. If it is solid, it has valid digital data to send. I'll have to check to see if the "data present" tally strobes when in DCM. If it doesn't, I'll have to look further. There may be a test point to pick off the DCM (I know there is for an ACM) where by you could use the test point in conjuntion with a DTS relay board to switch the SDDS out whenever it is in ACM or DCM...I'll investigate.

Steve

SDDS has an error correction mode called DCM (Digital Concealment Mode). This mode is not a backup mode but error correction if there is minor data loses on one track. Even if the track goes to DCM it cannot be heard unless the DCM is of a long duration. Most DCM's are of very short duration. If a DCM occurs in both tracks then the system will fallback to first fallback selection.

While I am not the clear expert I am assigning John Luttrell to monitor all forums and to respond to technical questions that arise. We will not comment on other equipment or manufacturers.

If you have a beef I will be happy to take your call.

If you have a technical question please contact John through our Technical Assistance Network. (201) 833-5333 the press 8 for Cinema products and then 2 to speak to an engineer.

John will be making a new post that will outline all contact information and our new 800 #.

Again my # is 310-244-7415. If you have questions other than service, parts or emergency technical help I look forward to hearing from you. If I am not in the office I will get back to you ASAP:-)

Al

I am posting again with my Signature attached this time.

Al

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********************************
Al Barton
Sony
GM SDDS Customer Support Group
GM Digital Cinema
10950 West Washington Boulevard
Suite 200
Culver City, CA 90232

I wonder what are the benefits of a "digital backup track" or DCM. Why "waste" space on print with that type of data?
I believe that a if an analog reader is well calibrated you cannot hear the Digital/Analog drop in quite scenes; and in loud scenes you'll probably hear the DCM drop since it is a Mix of channels.
I never heard an SDDS movie; perhaps I'm wrong. But this is my opinion.

So, why use print space for DCM? Why not use ALL the available space for SDDS High Quality track?

201.833.5333 Technical Assistance Network (T.A.N.)
press "8" for Cinema Products then "2" to speak with an engineer
866.SONYBPC toll free
techsupport@sdds.sony.com - email technical support <A HREF="http://www.sdds.com" TARGET=_blank>www.sdds.com</A> - sdds website for information on sdds, products, films, and software downloads.

Thank you,

John Luttrelle
Sony Cinema Products
Customer Support Group
10950 W. Washington Blvd
Culver City, Ca. 90232
866.766.9272 press "1" then "8" then "2"
john_luttrelle@scpc.sony.com

-hogan

That's the easy way out, but it's cheating the audience who deserve tho hear the movie in digital sound. Has your service tech looked at the problem? When is the last time the sound system was aligned and checked out? Does it happen more on one projector than the others? Does it occur on all prints, on a few prints, or only after prints have been running awhile so projector abrasion of the edges is taking its toll? Problem solving involves gathering data, looking for correlation with the problem, and then taking action to fix the suspected cause, whether it be alignment, marginal track quality, or abnormal projector abrasion.

Now that Sony is participating in Film-Tech, and has given additional contact information, their experts are on hand to help you get the best performance from the system, working with your service engineer.

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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

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Al Barton and John Luttrelle both work for Sony Cinema Products (SDDS).

You can tell which track is failing in DCM by popping open the front panel and looking at LED's 400 and 401 on the DSP-82 board I think. (Not at a machine to check ) They relate to each side, so say LED 400 is off and 400 relates to P-Side, then the P-Side track is failing.