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.)
Posted by Max Biela (Member # 1919) on 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 ![[thumbsup]](graemlins/thumbsup.gif)
Max
Posted by Gordon McLeod (Member # 33) on 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
Posted by Daryl C. W. O'Shea (Member # 1303) on 10-21-2003, 09:21 PM:
Oops, I thought I read CP55, sorry Manny. ![[sleep]](graemlins/sleep.gif)
Posted by Manny Knowles (Member # 1171) on 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.
Posted by Max Biela (Member # 1919) on 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
Posted by Gordon McLeod (Member # 33) on 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
Posted by Ron Yost (Member # 1850) on 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. ![[Smile]](smile.gif)
Ron Yost
Posted by Steve Guttag (Member # 268) on 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
Posted by System Notices (Member # 2357) on 02-24-2008, 02:34 AM:
It has been 1584 days since the last post.
Posted by John Hawkinson (Member # 1135) on 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
Posted by Warren Dewey (Member # 3609) on 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.
Posted by Michael Coate (Member # 757) on 02-25-2008, 03:04 AM:
![[joe]](graemlins/joe.gif)
gave me a pretty cool Dolby SR bumper sticker though.
![[Eek!]](eek.gif)
