Dolby Atmos 3D Panner 'Size' Issue

When sending a simple audio track to the Dolby Atmos 7.1.4 bus and also a duplicate 7.1.4 bus, why is the 'size' parameter affecting the upmixing differently between busses as shown in the animated .gif screen record? Left/Right, Front/Back, Down/Up, Rotate & Tilt adjustments all appear to affect both busses outputs identically and as expected. The 'Size' parameter never seems to get into the height channels of the duplicate 7.1.4 bus, in fact disappears into the center channel if anything, so is this a bug or by design? If by design, how can you use the size parameter to bleed the object into the other channels the same way as the Dolby Atmos Renderer s doing to the bus output?

3DPanner.gif (418.59 KiB) Viewed 816 times

Bus 1 is the Atmos Renderer whereas Bus 2 is a fixed channel 7.1.4 Buss.

Tracks routed to the Renderer are treated as Objects and will include positional metadata, whereas Busses are treated as Beds (standard fixed channel components).

Note that the Renderer does not support the 7.1.4 format (7.1.2 is the widest configuration for Beds).

To bleed in to the side channels of Buss 2 enable the 2D option for the Size parameter in the Panner, Front/Back will bleed in to the rears and Down/Up will bleed in to the height channels.

Thanks for the reply Reynaud, very interesting. I purposely made the copy bus 7.1.4 to match the Dolby Atmos 7.1.4 bus playing the audio track as an object not in the bed as I already noted the 'size' parameter effect was replicated identically to a 7.1.2 copy bus.

I wasn't aware the 'size' metadata affects a Dolby Atmos 7.1.4 bus for the renderer, but not a Dolby Atmos 7.1.4 bus not going to the renderer. Very interesting subtle difference, thanks.

AtmosSize.png (188.56 KiB) Viewed 471 times

If anyone is interested in a workaround for this, here is one way to duplicate the 7.1.4 Dolby Atmos Renderer bus to a 7.1.4 format non-Atmos bus. Basically loopback the 7.1.4 monitoring output and patch that to the input of a 7.1.4 audio track which outputs to a 7.1.4 format bus. This is important if you wish to apply your own binaural rendering to a 7.1.4 monitoring bus because alas, DaVinci Resolve's Dolby Atmos Renderer, doesn't include a binaural monitoring mode, only speaker monitoring or 2.0 headphone. If the 7.1.4 audio being binauralized in your own 7.1.4 monitoring bus isn't the same as what the render 'would' binauralize if it could, there will be unpredictable results and decisions made.