Film-Tech Forum ARCHIVE: Unusual sound problem with Dolby Digital

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Posted by Thomas Pitt (Member # 4322) on 06-21-2007, 01:31 PM:

Almost every time I see a movie, there are at least three places where for a split second, you hear what sounds like a triangle wave instead of the movie soundtrack. This is sometimes accompanied by a couple of seconds dropout to the 2-channel analogue soundtrack, other times the Dolby sound comes right back. The noise, I assume, is caused by the error rate suddenly jumping up to 8 or 9, then going back down - or perhaps the reader 'missing' a couple of data frames. But if that's the case, surely the sound should drop back to the analogue audio without any unusual noises?

Has anyone experienced this before? Or indeed, has anyone seen the Dolby error rate jump up seemingly at random, then go down again?

Posted by David Stambaugh (Member # 1102) on 06-21-2007, 01:48 PM:

This sounds like it's the phenomena others have described when the error rate briefly hits "F" but it doesn't drop out to analog completely. If it was mag tape it would sound like a splice in the audio.

Posted by Louis Bornwasser (Member # 3063) on 06-21-2007, 06:38 PM:

The error rate is not exactly the same as fault. It is possible to have low numbers and still fault. Likewise it is possible to have high, steady numbers and never fault. The common denominator is that the longer you go with no errors, the lower the number will go; TIME is also part of the equation.

Usually high numbers and faults go hand in hand; mostly because of incorrect set up on the player. Of course bad film will appear to be the same as bad set up. Louis

Posted by Monte L Fullmer (Member # 2797) on 06-22-2007, 02:55 AM:

using opaque tape, which blanks out four squares of the SR-D track can cause this 'bloop' since the switchover between digital an optical isn't fast enough. Or, using zebra tape that covers the same area of the film.

Why of the invention and usage of "Splicemark" zebra tape - one side of the tape has thinner markings than the other so the thinner side would go where the SRD track is and not covering this section of the film.

But, unfortunately with some booths supplied with "Splicemark", the training on how to use the tape correctly isn't applied..

-Monte

Posted by Max Biela (Member # 1919) on 06-22-2007, 06:08 AM:

Take a closer look at the soundtrack, here in Germany nearly all movies are now encoded with some kind of audio-CAP code ("bleeps" in SRD, "clicks" in DTS). Sometimes "clicks" are scratched into the analog soundtrack as well. SRD is completely scratched away to let the processor revert to SR.

Are these bleeps all in the same reel?