This is topic Balancing Dolby SR and Dolby Digital levels in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=001354
Posted by Michael Barry (Member # 237) on 08-27-2000, 01:19 AM:
In one of our auditoriums, there is a huge difference between the sound level of SR and Dolby Digital, so that when a tag starts in SR and switches over to Digital, the volume drops to about half of the SR level. The equipment is a CP-55 with an SR-A5 and a DA-20.
Does anyone have a suggestion for increasing the level of Digital to closely match SR?
Posted by Antonio Marcheselli (Member # 373) on 08-27-2000, 02:56 AM:
Usually the problem come from SR and not from Digital.
Did you often check the SR level with a cat. 69T?
That print has a tone recorded at reference level so that you can set your decoder to have a well defined input level.
Once I have the SR level of the second projector too high, so at the changeover I had to turn down the volume of 1 point... Just for one day of course, the same night I performed immediately a new dolby tone!It is impossible that Dolby Digital has levels too high than SR since the level volume are the same for SR and DD.
I suggest you to check the SR gain with 69T at least once a month.
Bye,
Antonio
Posted by Gordon McLeod (Member # 33) on 08-27-2000, 08:46 AM:
How much loader is it
It is possible that the a chain is off and another possiblity is that the DA20 is set for the wrong processor.
Also DD is a discrete system if you A chain azimuth on the optical is off it would cause the matrix to smear all the channels giving the effect of loader
At the 50% reference point DD and SR are the same but DD has far more headroom
Posted by Leo Enticknap (Member # 534) on 08-27-2000, 10:30 AM:
Setting the gain with a Dolby tone film should always be part of the normal routine. The level drops off less with LEDs, but with normal incandescent exciter bulbs their light output will fall by up to 30% during the course of their lifetime, with a consequent reduction in the strength of the signal being passed to the processor.At the last cinema I worked which had incandescent exciters (Philips FP-20s and CP45s), we Dolby-toned every fortnight, and a slight adjustment was usually necessary.
That having been said, the changeover to high magenta and cyan soundtracks is really going to cause hassle. If you set the gain for a conventional soundtrack fader setting being the same as digital, then a cyan or high-magenta track will need a very different level, and vice-versa.
L
Posted by Michael Barry (Member # 237) on 08-27-2000, 11:08 AM:
Gordon: SR is twice as loud as DD.
Posted by Gordon McLeod (Member # 33) on 08-27-2000, 11:31 AM:
Check the a chain level
has it always been like this?
if you can get a copy of DOlby Jiffy run it and obsereve with a spl meter the level of the pinknoise at the beginning. It should be around 85dbc in the house
double check the settings on the da20
Posted by Michael Barry (Member # 237) on 08-27-2000, 11:04 PM:
Gordon: Will check A-chain level...how can you verify the correct settings on the DA20? There is a manual there so I'll see if it's mentioned in it...although it may only appear in the installation manual, not the user manual...I just started working there so I don't know how long it's been like that...
Posted by Russ Kress (Member # 461) on 08-28-2000, 12:36 AM:
I just dealt with this!!If you are using the latest software revision, just run some 69T and verify Dolby Level for your analog decoding.
BUT!!!
If you are using older software where fader levels are pre-set by format instead of the processor "remembering" the last fader setting (CP-500), make sure that both formats are set at the same level. I have one processor out of eleven that still has this software, and it gets me every time! (LOL)
Speaking from experience, it is easy to neglect the analog optics since they have progressed to a back-up status for the SRD.
Just because we are using LEDs instead of exciter lamps doesn't mean that they won't change with time (or fail for that matter).
The print in question (The Cell) was just moved to this particular auditorium this week. The SRD failure is on a part of one reel of the print. The levels were matched in the previous auditorium so the drop out was not noticed until the move.
Analog sound will never go away. Digital failure is too absolute.
I prefer the seperation of digital, but the soundtrack is too fragile. Analog can fail in degrees, but digital (in any format) is either there, or it isn't.
Give me digital sound!! But on a Saturday night, give me a good SR encoded analog back-up as well!
After repairing the defective LED, we ran in digital and let the drop-out happen. No one noticed.
I think that Spectral Recording could have been a mile stone in the recording industry had "digital" waited a few years before becoming such a magic word.
Heck, just compare the dynamic range between the two mediums.
Russ
Posted by Brad Miller (Member # 2) on 08-28-2000, 02:06 AM:
Russ, he's got a CP55, not a CP500. 
Besides, if you have to change the fader on the default to SR, there is something off. Michael, I've seen bad Dolby tone test film that was severely "off", for lack of a better term. Get yourself another loop as a different opinion. Without a full A-chain, you can't be positive, but that should be checked for verification. I've never ran a DA20 through a CP55, but I have a feeling it may be a compatibility issue as no DTS unit I've ever installed on a CP55 was ever able to achieve high enough playback levels to match the analog on a CP55.
Posted by Michael Barry (Member # 237) on 08-30-2000, 07:56 AM:
Well done, everyone! It turned out to be the A-chain...the dolby levels were WAY too high. Once they were reset correctly, the levels between digital and analog matched perfectly. The switch between the two is barely detectable now, the way it should be...thanks again!