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#1
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Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
Hey dear Atmos buffs,
while setting up a 7.1.4 Atmos Studio with production suite I discovered a mixdown oddity which apparently can’t be affected with neither setting of the “trim and downmix controls”. Here we go: A signal panned to (+/-)60,60, 60, 100 = (TopFront R or L) is mixed down vastly different depending on being “object” or “7.1.2 bed”. In essence, when I toggle this exact panning between Object/Bus in Protools and the monitoring in the Renderer is in “Stereo downmix”, the object mode results in about double volume than Bus mode! This happens only with the top fronts. All other speakers mix down as expected. When I dig deeper into it I see the first difference appearing in the 7.1.4/7.1.2 to 7.1 downmix/monitoring where Objects in this position are fed partially into R,C,Ls,Rs whereas Bed content in this position is exclusively downmixed to Rs. The Object pattern goes down to the 5.1 and then adding up in overly loud reproduction in the Stereo. It gets even weirder! When I do the same experiment with a 7.1 Bed (instead of 7.1.4 Bed) the contrary happens. The object is mixed down lower than the bed! Less difference but still considerable. What the heck? As I said, no setting in the downmix controls affects this being so. To compare I set up my own straight downmix matrix for quick reference with the awesome RME total mix matrix and these DIY downmixes behave exactly as I would expect. No overblown objects in the stereo. What's going on here? Top Front Objects mix down into Stereo a lot louder than 7.1.2 beds? Top Front Objects mix down into Stereo lower than 7.1 beds? So different that it isn’t the same mix at all. I´m sorry for this complicated matter but can anyone confirm this? Do I have my wires crossed or is this what the Renderer does? Thanks so much for help Nick Mojave, 6 CoreTrashcan PT 2020.12 Ultimate native Dolby PS Renderer 3.5, Dolby Audio Bridge In, Aggregate Out (Fireface,DAB) Edit: I just could exactly reproduce this on a different computer Last edited by Nick Camaron; 02-18-2021 at 03:32 PM. Reason: Sys info added |
#2
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Re: Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
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Composer/Sound Designer/Protools 2024.3 Ultimate, MTRXII-TB3, DADMAN MOM, Cisco SG350-10MP EthernetHUB, KLANG:quelle 4 Channel Dante™Headphone Amp, DVS,MADI, Mac Studio Ultra,128 RAM/4TB SSD, Ventura 13.6.6, DP 11.3.1, Logic Pro X 10.8.1 DOLBY ATMOS Facility/MPSE Motion Picture Sound Editors Avid Certified Professional ProTools/Dolby ATMOS |
#3
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Re: Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
Ok thanks. How to contact Jeff though? Hello Jeff, you hear me?
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#4
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Re: Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
OK, without knowing the specifics of what you're doing in your home-brew downmixer, I'm guessing that the discrepancy lies in the values in the front height channels possibly summing with signal already feeding the 7.1.2 bed?
I would love if somebody could explain why Avid and Dolby settled on a max bus size of 7.1.2, and not 7.1.4? I've taken to avoiding using the .2 in the bed, and creating a Quad bus that feeds 4 object paths for the .4 If that's what you're doing as well, then I may be facing the same downmix dilemma you're discovered. Have you measured with a tone to calculate the exact level differences? Is it possible that the pan-law for your height objects (if you're also using a Quad bus?) is set to one of the optional shapes? Is it possible that you have some binaural processing going on that might be causing this? |
#5
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Re: Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
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7.1.2: Rtf Objects switched to 7.1.2 bed are summed -3dB to Rtf+Rtr. These Rtf+Rtr are summed -4.5dB(?) to RS only in the 7.1. This seems to result in a 6,3 dB dip in the Stereo Mixdown(compared to object mode) 7.1: Rtf Objects switched to 7.1 bed are more or less adequately distributed to C,R,Ls,Rs resulting later in a 3dB boost in the Stereo Mixdown. (compared to object mode) (Values read out on the short term Loudness measurement in DAR) So these are my findings. Please don't nail me down on these since I´m just investigating and I might be confused. But when I am right there is a 9,3dB!! difference for Rtf Objects toggled to Bus, depending on 7.1 or 7.1.2. My conclusion then is to steer clear of 7.1.2 beds totally. 7.1 beds are not perfect either but seem to be close enough to get halfway corresponding mixdowns. Quote:
It appears that in wedge mode the discrepance is alleviated due to automatic avoidance of extreme Tops position. When I get that right. But thats just a workaround I´m afraid. Quote:
Phew this is a difficult one and it is hard to phrase this correctly. I need a coffee break now cheers Last edited by Nick Camaron; 02-19-2021 at 04:41 AM. |
#6
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Re: Dolby Atmos Top Front Content: Object vs. Bed=huge difference in Mixdown.
Unrelated and probably a bit stupid question: how do you route quad bus to objects? I have only managed to route mono and stereo busses to objects.
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