Film-Tech Forum ARCHIVE: Dolby 701 alignment per frames?

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Posted by Paul Vollmers (Member # 927) on 11-02-2011, 09:27 AM:

I have just installed a Dolby 701 on my Simplex E7 and I'm trying to figure out a way to align the Reader with out the Cat 1010 film.
Is there a way to count frames or sprocket holes from the gate to the reader?
DTS I have setup just fine.

Posted by Randy Stankey (Member # 64) on 11-02-2011, 09:55 AM:

The Dolby film makes it faster and easier but you don't need to buy that film unless you want to. (Or if you have several of machines to set up and maintain.)

Just thread up any old piece of film, use a Sharpie marker to mark the sprocket hole that is at the scanning point of the Dolby reader then mark the sprocket that is at the scanning point of the analog sound reader.

From there it's just a matter of counting the number of sprocket holes between Point-A and Point-B.

Posted by Louis Bornwasser (Member # 3063) on 11-02-2011, 10:46 AM:

2 cheap ear buds. One connected to optical center off the processor, the other connected to center channel of the Da-20. Adjust for no echo. Louis

Posted by Tony Bandiera Jr (Member # 2365) on 11-02-2011, 12:52 PM:

As I sent in an email to Paul, I believe you can get the setting in the ballpark with the following method:

Thread a piece of film with clearly defined framelines;
Mark the frame at the analog reader;
Mark the frame at the digital reader optical center;
Count the total frames and multiply by 4 to get the perf count;
Subtract 26 from the total perf count and that is your offset.

That should get you within 4 perfs (one frame) of the correct offset.

I will be at UCI tomorrow and will try this out to see how close it is. [Smile]

Posted by Scott Norwood (Member # 30) on 11-02-2011, 01:25 PM:

I always just used the numbers in the manual (I forget if it is the DA20 manual or the CP500 manual or both that gives the common offsets for most popular projectors) as a starting point and then adjusted by ear while comparing the sound with the analog output. Obviously, the manual part will not help if you have an SDDS or DTS reader mounted below the cat. 701.

The offset adjustment is actually a strong point for SRD (or a weak point for DTS): DTS (at least the 6D) only allows adjustment of the reader offset in whole-frame increments, while Dolby allows adjustment in 1/4-frame increments. This reduces the annoyance factor when the digital system reverts to analog and also increases the chances of getting correct sync in the auditorium (expecially in smaller houses).

Minor nitpick point: in 2-projector installations, the offset needs to be the same for both projectors (this is also true for DTS...not sure about SDDS). This can be annoying in some circumstances (for example, it is not possible to use a penthouse reader on one projector and a basement reader on the other projector).

Posted by Randy Stankey (Member # 64) on 11-02-2011, 01:29 PM:

Yeah, I count the frames and multiply by four as well. Then count the odd sprocket holes and add or subtract as needed.

Posted by Tony Bandiera Jr (Member # 2365) on 11-04-2011, 12:15 AM:

I stand corrected on the above post, you need to ADD 26 perfs, not subtract.

Amazing the things one thinks of on the commute home from a screening.

Posted by Paul Vollmers (Member # 927) on 11-05-2011, 10:40 AM:

Yep..adding 26 perfs made the alignment for the 701.
Picture and sound is just fine now.

Many thanks to all that helped out.