Atmos bug: phase weirdness with "size" parameter

[moshuajusic]

Looks like it's a PT issue since exporting a master file and importing it into Logic, using Dolby rendering there, and increasing object size, the phasey tone is gone.

https://professionalsupport.dolby.co...language=en_US

PS - since we can't use Dolby's music panner plugin with the internal renderer, it'd be nice if Avid would add some basic shapes to the built-in surround panner, like circle.

[audiogamble]

Is this happening on the binaural fold downs or just stereo fold down?


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[moshuajusic]

Binaural. I haven't checked vanilla stereo. I'm using "live rerender" to monitor.

[audiogamble]

Thanks for reporting this. Good to know.

To be clear, this is only present with the internal renderer? Do you hear it during live monitoring, or just when bouncing re-renders offline? Do you also hear this with re-renders bounced from the latest Dolby Renderer?

What has been your workaround so far?

I'm using Pro Tools 2023.12 and Renderer 5.2 . I am connecting an external renderer, and offline bouncing from pro tools. Re-renders are generated from the Dolby Software by importing the ADM. So far, I haven't experienced what you're describing.

[moshuajusic]

I get it with all live rerenders, 2.0, binaural, 5.1. I also get it when bouncing a rerender. My workaround is to just ignore it for now since I'm checking my work in Logic anyway where the issue doesn't happen. So at least the ADM BWF master files bounced from Pro Tools are ok (which is ultimately what would be distributed). It's their rerenders and headphones monitoring at issue.

I was mainly just bringing the Dolby forum topic over here since it's evidently a Pro Tools issue. You can read others who've done more tests like the ones you're suggesting (including external renderer).

[mattrixx]

Yeah, I think there's going to be a lot of refinement in the coming months, however, for me, I am happy to stick with my DAR workflow for now.
Great advances in PT workflow however. Will only get better & better, that's for sure.

[Frank Kruse]

The issue set aside, I'd highly recommend to avoid any sort of divergence (size in Atmos speak) for Atmos. Feeding the same mono signal to multiple channels can cause unwanted balance changes in the downmixes because you're essentially summing the identical signal from multiple feeds. Also because the speakers don't have delay applied and have equal level (unlike with other surround formats) you can get weird unwanted Haas effect (mis-)localisations if you have the identical signal coming from different speakers when using size so this can also happen when playing the original format in a large venue. It can become rather unpredictable depending on where someone's sitting. Personally I don't use size for these reasons.
Just my two cents...

F.

[Michael Carnes]

Originally Posted by Frank Kruse

The issue set aside, I'd highly recommend to avoid any sort of divergence (size in Atmos speak) for Atmos. Feeding the same mono signal to multiple channels can cause unwanted balance changes in the downmixes because you're essentially summing the identical signal from multiple feeds. Also because the speakers don't have delay applied and have equal level (unlike with other surround formats) you can get weird unwanted Haas effect (mis-)localisations if you have the identical signal coming from different speakers when using size so this can also happen when playing the original format in a large venue. It can become rather unpredictable depending on where someone's sitting. Personally I don't use size for these reasons.
Just my two cents...
F.

I've done some thinking about this. I suspect the size actually feeds to peripheral channels by some type of decorrelation (perhaps a short allpass or FIR). You can hear the overall enlarged signal as sounding just a bit more distant or 'fuzzy'. Pure speculation on my part--Dolby doesn't publish anything about this that I'm aware of. The problem with this sort of short decorrelation is that there can still be all sorts of cancellation, depending on the size of the mixing or listening environment. So I don't know that the signal is identical at each speaker, but it's close enough that the problems Frank points out are quite real.

I don't know that there's a real solution to this. Size of the venue, flight time from each speaker, characteristics of the material will give a broadly variable experience. I'm just an old retiree doing Atmos music for fun, but I find myself avoiding size in almost all cases. I'd be more inclined to put a short reverb on each wall and set up a group of sends for them. The send level would then act as size. Of course this is a royal PITA, so I don't bother.

[moshuajusic]

I was avoiding size but found that Apple and Dolby treat both volume and size differently. If I increased a reverb volume, Dolby would sound washed out while Apple would sound as intended, or decrease the reverb and Dolby would sound as intended while Apple's own weird room sound would take over. (I friggin hate Apple's headphones rendering compared to Dolby's.) Adjusting size was a way for me to get similar sound in both.

I've been in an Atmos studio and use Beats Studio Pro to check Apple and headtracking at home. Most stuff that the renderer graphic shows swirling and zig zagging around I have no perception of even with 0 sizes. In my own mixes with some larger object sizes, direction and headtracking is perceptible. There's definitely a point where increasing size starts making it nondirectional. But I'm typically in the 5-40 range.

That's another Pro Tools quirk: size in the surround panner GUI can swell to take up more than the whole room, but the same value shows up not even half the size in Dolby's GUI and in Logic.

[thierryd]

Size is a thing to be careful with in Dolby Atmos, the same goes for the .2 of a 7.1.2 bed. A couple of years ago, when Apple introduced Dolby Atmos with a twist on iTunes, I did some experiments and posted the results on Youtube, with various stereo, binaural (NEAR-MID-FAR) etc renders of the same mix. It was a learning experience. Here's a link to one of the videos: https://www.youtube.com/watch?v=RB15gZmC-KQ&t=328s
you'll find the others on the same YT channel and also 360 versions of Ambisonics renders out of the same Dolby Atmos sources on my Listen to 360 YT channel (also very revealing for the way the technology works).


Greetings,


Thierry