Film-Tech Forum ARCHIVE: Sound format 10 Reverted optical Dolby !!!

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Posted by Duc Nguyen (Member # 6988) on 06-24-2012, 10:34 AM:

Hello all,
When I run some films, Dolby Digital is changed "Reverted optical Dolby" at some reels. And film Vol. is down. Pls help me fix it. I use CP650 and FP50A Kinoton projector (35mm). Thanks.

Posted by Paul H. Rayton (Member # 1817) on 06-24-2012, 10:41 AM:

It means that the Dolby Digital track is not playing -- most likely (since you say it occurs on "some" films) a problem with the reader. How long has it been since the LEDs were checked for brightness and alignment? Typically, if those are set correctly, most all Dolby Digital tracks will read, except those that have serious scratching between the perforations. If you don't have the test equipment, you need to check with your tech to see what's up with that reader. (LEDs age, over time, and get dim. They may need to be replaced, if they've been in use for several years.)

Posted by Martin McCaffery (Member # 37) on 06-24-2012, 10:45 AM:

Welcome to the forum.

Your description seems to indicate the digital track on the print you are running is bad on some reels and the CP650 is reverting to Optical Stereo. This is the desired result with a bad track. If you check the LED screen on the CP650, you should see an "F" indicating a fail.
If this is only happening on this print, then it is likely a print problem. If you are running duel projector and it only happens on one projector, it is time to call your technician in to do adjustments.
The sound difference between the two is the result of the levels not being properly set between the two formats. You should contact your tech person.
In the meantime, just run the film in SP and adjust sound accordingly.

Posted by Manny Knowles (Member # 1171) on 06-24-2012, 11:30 AM:

I think Martin ^^^ meant to say "run the film in SR" (not SP) -- use format 05.

But... to force your processor to remain in "analog-only" mode, you will have to turn off auto-detect or auto-target or whatever Dolby calls it, otherwise it will continue to automatically revert to digital whenever it detects usable data -- and that is the problem you have now -- it is switching back and forth between analog and digital all by itself. Disable the "auto digital" mode and the unit will ignore the digital track.

When you get the system repaired -- or if you switch to a print that has no damage -- you might consider re-activating the auto-digital feature.

Now, for your second issue -- Your analog-optical sound is playing at a significantly lower level, compared to digital -- you probably just need to calibrate the analog signal levels. You may need to increase brightness of the light source in your analog reader and/or the input trims of the Dolby processor.

Some questions:

Single projector "platter" or 2-projector "changeover" setup?

SINGLE PROJECTOR -- Does the system switch between analog/digital at the same parts of the movie? -- if so, it means the digital "track" is damaged -- there's probably nothing wrong with your digital reader.

TWO PROJECTORS -- Does the analog reversion happen with only one projector?

* Step 1 -- Take one of the "bad" reels and try it on both projectors. If you still don't get digital, then the reel is probably at fault.

* Step 2 -- Double-check -- Take one of the "good" reels and try it on both projectors -- does the digital track play on both machines? And do you get the same error correction score both times?

If you get different scores then definitely the digital reader that produces the higher number (worse score) needs alignment -- but get them both checked out -- there may be room for improvement in both cases.

Posted by Adam Ladds (Member # 6757) on 06-25-2012, 01:37 AM:

We had this problem just after some joins went through the projector, and it turned out to be a poorly made join causing the frame to jump up, increasing the tension on the film across the sound reader.

Re-making the joins carefully would usually fix it. Make sure your splicer is set correctly, too.

Posted by Duc Nguyen (Member # 6988) on 06-25-2012, 04:12 PM:

Thanks everybody,
I think, my problem is LED reader. My system have worked for long time.
This happened at some screens or some reels .And new movies iis still like that. But this just happened in some projectors.
When the movie played at those screen, i changed to format 05 and adjusted vol. up. But sound effects are lost. My customers complain because of vol. changing regularly.
@Manny Knowles:
SINGLE PROJECTOR -- Does the system switch between analog/digital at the same parts of the movie? -- if so, it means the digital "track" is damaged -- there's probably nothing wrong with your digital reader.---> right, but when i played that movie in other projector, the sound was good.

TWO PROJECTORS -- Does the analog reversion happen with only one projector? yes, it does.
@Martin:
"The sound difference between the two is the result of the levels not being properly set between the two formats." How set the levels between 2 format correct?

Posted by Randy Stankey (Member # 64) on 06-25-2012, 06:08 PM:

In order to set the levels on a CP-650 you need a specially calibrated microphone and an S.P.L. meter. If you want to equalize the system, you'll need an oscilloscope. If you want to tune up the Dolby reader on the projector, you will also need some test film. You should also tune up the analog reader in the projector. That requires about three other test films. Additionally, you will need tools such as Allen wrenches, screwdrivers, etc.

The process isn't difficult. A competent person should be able to do it in an hour or so. The problem is that the process is very detail-oriented. There are several small details that must be done correctly and in the correct order, else you won't do any good at all or, if you do it poorly, can make the sound worse than when you started or even damage equipment.

Get a technician. The price you pay for his services will be well worth it.

Posted by Manny Knowles (Member # 1171) on 06-25-2012, 06:15 PM:

If it plays on one projector but not the other then the reader needs alignment -- get a tech -- and have him/her check digital and analog on both projectors -- or however many you have.

Posted by David Favel (Member # 1125) on 06-28-2012, 01:10 AM:

Is the led near the end of its life?
Can you increase the power to the led?
(Mine has a level adjustment on the power plug)