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Topic: Cinema room calibration test tone suggestions
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Harold Hallikainen
Jedi Master Film Handler
Posts: 906
From: Denver, CO, USA
Registered: Aug 2009
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posted 06-13-2015 11:50 PM
The JSD-100 drops side surrounds and rear surrounds by 3dB if you're in a 7.1 auditorium and play 5.1 content (surround content driving both side and rear surround). The JSD-60 input mixer can be set to whatever you want, but the manual suggests a 3dB drop in this circumstance (mix coefficients of 71%). There was an interesting discussion about this on the pink noise SMPTE group recently. The discussion that IF you were to fade from one speaker to another, how far down should the speakers go when you're half way (equal power in each speaker). It was suggested that if you drive the speakers with equal power and are on the centerline between the speakers, the pressures add, so you're up 6dB. But, if you are not on the centerline, powers add, so you are up 3dB. As a compromise, a lot of panners (ie, Pro Tools) drop 4.5dB when you are at the center of the pan.
Harold
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 06-14-2015 10:41 AM
See? I like how this little nuance is not so cut and dried amongst the various implementations. The QSC DCPs don't do it either but you can burn through one of your EQ presets to create it. I hear that on an upcoming firmware, they are going to have the automatic level setting for 7.1.
The problem with surrounds is people like em loud. I can't tell you how many times I hear people spout their evaluation of a movie soundtrack based on surround activity. Go over to Cinema Treasures for the Mid-Atlantic area Theatres. So if you ignore setting the levels right, then 5.1 gets a boost of 3dB and those types of people love it...forget about that is not what the guy mixing the movie thought was right.
I also think an opportunity was missed to leave mono surrounds back to the film era. With DCP it was established that 5.1 was to be the MINIMUM sound format to be supported. As such, why the 82dBC/side? That was to accommodate mono surrounds of the film era such that a split surround mix and a mono-surround movie would play identical in level. This was especially true in its origination on 70mm where format 43 used the mono surround track below 500Hz to mix with stereo surrounds on tracks 2 and 4 above 500Hz...track 6 was used for surrounds on both format 43 (5.1) and format 42 (4.2). Yes, in its inception, format 42 had stereo bass since it was often playing out of LC/RC speakers. Even Surround-EX had to bow down to the mono surround level. A proper EX decoder would take -20dBFS signal from Ls/Rs channels and only play 85dBc from the entire rear channel despite having a 6dB increase in source level. As such, if you had a mono surround theatre and played PN from "S" channel, it was 85dBC, if you had 5.1 and you played PN from both surrounds you still had 85dBc total (82dBc/side) or if you had an EX theatre, you still had 85dBc but just from the rear speakers. If you turned off one of the surround PN sources, then it would be 82dBc in EITHER of the 5.1 or EX theatres.
We don't have that legacy in DCinema...5.1 is where we are starting. So 5.1 should have been the thing everything else had to be able to be compatible with, not 4.1 or 4.0 from film.
This is the stuff about DCinema that makes me roll my eyes a bit. ![[Roll Eyes]](rolleyes.gif)
It would have been clear that it was on the sound processor's to put in the necessary pad when playing a 5.1 track in a 7.1 surround configuration. If you want to add a fancy feature above the standard, then it is incumbent upon you to make sure your product is fully backward compatible.
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