But are mix engineers mixing in 10.1.6? I know that 9.1.6 is becoming more prevalent in Atmos mix rooms, but 7.1.4 seems to be the standard for Atmos mixes.
If a song or album is mixed for 12 channels in a 7.1.4 configuration, where does the Atmos algorithm derive the source for the 10th channel?
No clue, we need to hear from someone who does Atmos mixing.
All I can tell you is that on the three Atmos discs I received Monday (Ziggy Stardust, Chicago IX, and No Secrets) that there are some instances on all of them of isolated instruments appearing only in Cb (or Cr, depending on the naming convention). Whether it is part of the rendering algorithm or part of the intentional construction of the Atmos metadata by the mixer I have no way of knowing. More generally in my experience Cr either simply supports Lr and Rr, or more often is silent.
If indeed mixing to Cr is being done, clearly the rendering engine can simply put content on both Lb and Rb in the case of 9.1.6, just as fake C is often done. Perhaps mixing to that Cr is more the default since falling back to 9.1.x is easy for the decoder.
I haven’t listened much with 12.1.10 to the new content, but the little I did do (with Ziggy Stardust) all of the channels were active. Whether that is being done in the mix or simply by the rendering algorithm, I don’t know. I do know that in the descriptions of Atmos metadata I’ve read from Dolby, metadata describe location and movement of objects, and the renderer maps these objects to the physical speakers present - so the mixer doesn’t mix to Cr, which is not part of any bed, but perhaps an isolated rear object described by the metadata can end up on that one speaker. Guidelines from Dolby give pretty narrow ranges for elevation and azimuth angles for each speaker governed by speaker label, and the Atmos definitions for the various listening rooms have strict speaker labels.
