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Author Topic: Distinguishing Dolby A Prints from SR Martin Brooks Jedi Master Film Handler Posts: 900 From: Forest Hills, NY, USA Registered: May 2002 posted 10-21-2003 12:06 AM                        quote: When Dolby realized that the big stumbling block for CDS was the need for the distribs to double inventory, Dolby began saying that the studios DIDN'T need to double inventory, that Dobly A and Academy tracks, miraculously became compatible...."no need to double inventory; playing back dolby A without decoding isn't THAT bad." Dolby claimed compatibility long before the advent of DTS. Larry Blake wrote an article about mixing for Dolby and issues of mono compatibility in an article for Recording Engineer/Producer in June, 1985. If you played back a Dolby A film without decoding, all other things being equal, you would hear an increase in high frequencies and also an increase in hiss. However, if the levels are relatively high enough to cover the hiss, then the Dolby processing was hardly in use anyway, and you wouldn't hear that much difference, since Dolby A works primarily on low-level, high frequency material. Experience with Dolby B shows that many people actually prefer playing back a Dolby B encoded tape without the noise reduction, because of the increased levels at high frequencies. I once heard Ray Dolby make that comment. He fully realized that most neophytes really had no idea what Dolby was. Remember that Dolby playback doesn't use the Academy Curve, it uses the X curve. Because the Academy rolloff is so steep, you actually don't hear much difference between playing a mono Academy soundtrack and a Dolby A soundtrack played back via non-Dolby playback. Although admittedly, I've never had the opportunity to A/B this. Playing SR via A or A via SR is another story. Because it's relatively full-range, one would hear all of the artifacts associated with playing back with the wrong processor. And aside from what would be perceived as EQ anomalies, since the processing would take place at the wrong frequencies and levels, I also suspect one would hear quite a bit of pumping in the audio level. Playing SR via A is probably a lot worse than playing A via SR.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 10-21-2003 12:39 AM                        Dolby doesn`t really use the X curve instead of the Academy curve. The X curve is for aligning sound systems to rooms.  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 10-21-2003 03:03 AM                        quote: Playing SR via A is probably a lot worse than playing A via SR. the word i've heard before is the opposite. while i'm not sure i've ever heard A via SR (wouldn't a processor that does SR probably do A as well?), we do play SR via A on 2 screens, and it doesn't seem too bad. in fact, aside from not sounding as "big" as our digital house, there is to my ill-tuned ears nothing wrong with it. except for when there is, and it's some other problem. carl  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 10-21-2003 05:59 AM                     Carl -- I was told the same thing about it being worse to play A in SR but I haven't ever been that curious about it until reading this thread. I'll give it a try and see. I have played Dolby movies in mono before with no apparent problem -- certainly no refund demands -- but the point is well-taken that encoded signals really ought to be decoded properly. As for automatically having A in an SR-equipped box...they aren't necessarily both going to be there...at least not at the same time. For instance, the CP50 doesn't have enough room for both SR and A NR cards and IIRC there are other processors where this is also the case. Cards have to be swapped, provided that the cinema owns a set of both types of NR cards.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 10-21-2003 06:02 AM                        Or you could use Cat 222 SR/A's.  |  IP: Logged Warren Smyth Expert Film Handler Posts: 158 From: Auckland ,New Zealand Registered: Aug 2003 posted 10-21-2003 07:35 AM                     Manny I'm in the very situation you describe with a CP50 upgraded to SR. I will hold on to the A cards though to run earlier prints where appropriate. I agree that anything encoded must be decoded correctly. I was just wondering what the audio encoded SR would sound like on A and the level of acceptibility. I would imagine slight pumping from tracking error (rather like that from incorrect dolby level). On a similar subject, I have wondered for some years, if a few mono films of the sixties and seventies had a pre-emphasis of high frequencies. The reason, most films if played flat without academy roll off may be noisy, but the eq is ok, even with a narrow slit. It's surprising in fact, what's on some of those early recordings. They can actually sound quite good played this way if you don't mind a bit of noise. In this instance, the recording curve drops off at about 8,000 cycles. Alternatively, some mono features play with what seems to be an abundance of highs and sound very toppy when played flat. They sound unbearable in fact. Naturally, the academy filter in the playback normally brings these highs back to the correct eq. Now the result of this would seem that the high fidelity of these recordings is increased. The academy roll off is still active and reduces noise, but slightly higher frequencies are reproduced than in previous recordings. The filter's curve is partially defeated by the pre-emphasis. Now I haven't seen confirmation of this documented any where. This apparent variation to some mono recordings however, makes me wonder if there wasn't an attempt in the mix, to increase the upper frequency range SLIGHTLY of these tracks some years before NR was introduced. I would be interested to read any comment.  |  IP: Logged Martin Brooks Jedi Master Film Handler Posts: 900 From: Forest Hills, NY, USA Registered: May 2002 posted 10-21-2003 12:29 PM                        quote: Dolby doesn`t really use the X curve instead of the Academy curve. The X curve is for aligning sound systems to rooms. Right. But any of Dolby's early literature will tell you that the room must be aligned to that curve, which was developed primarily by Dolby and adopted by the ISO in 1972 (ISO 2969). Before that, from 1938, theaters were supposed to EQ their rooms to the Academy Curve, although I'm sure many weren't equalized at all. (Before 1938, there was no one standard.) The Academy Curve rolls off much quicker (down 17db at 8K). My point was that any anomalies caused by playing back a Dolby A print on a mono non-Dolby system would probably not be heard (at least not the high frequency anomalies) because of the steeper Academy curve, although one of the reasons for the Academy roll-off was because of high frequency distortion in the old Altec A7 speakers. Of course this whole discussion is somewhat moot because how many theaters still have mono non-Dolby optical sound? And those that still have the facility are probably also playing back Dolby (and perhaps Digital) and are EQd to the more modern standard in any case. And just as a side point, while sound mixes for mag tracks were monitored (and supposed to be played back) without the Academy curve, no standard was ever developed (before the ISO2969 standard.)  |  IP: Logged Max Biela Film Handler Posts: 89 From: Dortmund, Germany Registered: Sep 2003 posted 10-21-2003 01:06 PM                     Daryl, how can you use a Cat 222 A/SR in a CP 50? Buy a used SRA 5 or the Adapter from Panastereo and be happy with it Max  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 10-21-2003 05:38 PM                     The academmy curve was a preemphasis on recording that accounted for many items and room eq was really not one of them the width of the playback slit (a 1.5mil slit will emulate on its own most of the rolloff) and the effects of the older speakers in themselves The X curve is independent of any recording curve used but is a tailoring of the room andspeakers etc to a predetermined curve  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 10-21-2003 09:21 PM                        Oops, I thought I read CP55, sorry Manny.  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 10-22-2003 12:18 AM                     Was there ever an SR1 adapter? I remember hearing that was what you would need to run SR from a CP50.  |  IP: Logged Max Biela Film Handler Posts: 89 From: Dortmund, Germany Registered: Sep 2003 posted 10-22-2003 02:53 AM                     Hi Manny, no, you just need a Cat No. 113C and and ext. SR-Adapter (like the SRA 5). Or just plug the two Cat 280 (wich are in the SRA-5)direktly in the CP, but then you can not switch between Dolby A and Dolby SR. Max  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 10-22-2003 02:42 PM                     Also Smart and UltraStereo made SR adapters to use the cat 280T or cloned cards and I think Peavey/CinemaCoustics did as well  |  IP: Logged Ron Yost Master Film Handler Posts: 344 From: Paso Robles, CA Registered: Aug 2003 posted 10-22-2003 03:38 PM                     I remember when Dolby B was all the rage in consumer audio tape equipment. It was awful! Good for classical and chamber music, perhaps, but death to R&R (my favorite music, then and now). Everyone I knew back then always turned it off, when given the option. Better to have a little hiss than dead music. Ron Yost  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-23-2003 07:42 AM                     Hmmm...I used Dolby-B extensively on R&R and R&B music back when it was "all the rage" and never had it kill anything but the hiss. Dolby-B like all of the other Dolby NRs depended on the system being properly calibrated. Above the Dolby Level.(normally 185nW/m on most tape players, was Dolby-Level. Anything recorded above that level received no compression or expansion, the circuit did not have any affect on the signal. If you get ahold of any of those decks from the 70s and even from the early 80s, you will find they have the doube-D symbol on the meters or some other indication of where Dolby Level was. It was not at 50% or 0-dB unless that is where if fell on a specific deck's meters. For compatibility, the level was referenced to the actual flux on the tape. In this way, a tape recorded on any deck should play correctly on any deck. That is the theory...in practice, most consumer decks were miserably calibrated and generated the response on the post above mine. In fact, Dolby-B did NOT kill any music or high-frequencies...it was quite transparent to the recording process and only affected low-level signals (when properly calibrated). When someone complains about Dolby NR (any of them) the problem really lies with their equipment, not the NR. If your recorder/player can't faithfully reproduce what was recorded or it is mis-calibrated, then it won't perform. None of my decks ever seemed to have this problem (even some of the cheaper ones). Now R&Rers did find they liked recording with Dolby on and playing back with Dolby off...the result was some mild compression in the high frequencies and elevated treble...the fact that some prefered that doesn't make it right and it definately is not the same signal that was originally recorded. The same result could be achieved without the Dolby NR circuit but it gave you all that with just the flip of a switch in the recording process. Now, if you played back a tape that did not have Dolby NR applied on the recording process then yes it will kill the music with over expansion and reduced Highs. Steve  |  IP: Logged

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