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Author Topic: Distinguishing Dolby A Prints from SR System Notices Forum Watchdog / Soup Nazi Posts: 215 Registered: Apr 2004 posted 02-24-2008 02:34 AM                 It has been 1584 days since the last post.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 02-24-2008 02:34 AM                     *dredges up thread* I still wish I had a more definitive way to test for A versus SR (see my Taxi Driver post in the FITA). I vaguely wonder how hard it is to tell analytically. If I grab the Lt/Rt tracks off my CP65 either after the preamp or at the post-NR testpoints on the Cat.150, and feed them into some measurement software... Or perhaps if I just measure the dynamic range of the track over the course of a reel and see if it crosses some threshold... (Alternatively, I guess I could measure of the 242's testpoints, post-matrix...) I don't suppose anyone has experimented with this methodology? --jhawk  |  IP: Logged Warren Dewey Film Handler Posts: 28 From: monterey ca usa Registered: Jan 2006 posted 02-24-2008 09:35 PM                        This is still an interesting topic-- I don't know that there is any official way to test for A vs SR, or how to tell clinically whether the equipment is actually processing properly. The dynamics of a sound mix are creative choices and they can vary a lot, so it would be difficult to measure for dynamic range. It's a moving target with program material. However it's fairly easy to develop an ear for distinguishing A from SR, and when a system is working right. Listening for split surrounds or looking at an LR phase display on a scope would identify SR, but this isn't always obvious. In the early days of Dolby processing in the music recording business, I carried a home made test tape of high, mid and low tones at different levels. If the system was working right it would reproduce the exact same varied levels in playback mode. Then you would adjust levels in record mode to match those output levels. The actual recorded level on the tape, however, showed much less variation due to compression in the encoding process. But still a lot of errors cropped up. Supposedly "Light My Fire" by The Doors was encoded Dolby A (one of the first recordings to use the process), but the mastering engineer who cut the disk did not have a Dolby unit. So the record was released with the bright, compressed sound of un-decoded Dolby processing. Occasionally I will get a "restored" print of an older, originally A-encoded title that is marked SR but is definitely still A-encoded, as though the original A sound track was just reprinted. Possibly an innocent mistake, but also an easy way for a facility to make money for a re-sounding job while not actually performing the work. Incidentally, the chip in the decoding section of a cp55 will also function as an ENcoder. I had a cp55 that had a resistor fail and a decoding chip began to compress the right front signal instead of expanding it. Needless to say the stereo effect got really weird.  |  IP: Logged Michael Coate Phenomenal Film Handler Posts: 1904 From: Los Angeles, California Registered: Feb 2001 posted 02-25-2008 03:04 AM                     quote: Warren Dewey it's fairly easy to develop an ear for distinguishing A from SR, and when a system is working right. Listening for split surrounds or looking at an LR phase display on a scope would identify SR, but this isn't always obvious. Since when has SR had split-surround capability?  |  IP: Logged Warren Dewey Film Handler Posts: 28 From: monterey ca usa Registered: Jan 2006 posted 02-25-2008 10:50 AM                        Sorry, I was wrong. My error. No split surrounds in 35 mm SR.  |  IP: Logged

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