Yesterday I had a long conversation with my good friend Erik G, and it was a real eye-opener.
The conclusion was that working in 7.1.4 does matter.
A lot.
The problem lies in the 5.1 downmix.
Working in 7.1.2 makes that any content we put in the .2 highs will be spread over the 4 high speakers by the Atmos Renderer , and therefore will be downmixed to the front and rears in the 5.1 folddown.
Working in 7.1.4 will downmix the front highs to the 5.1 LCR and the back highs to the Ls/Rs of the 5.1 folddown. Which means that a 7.1.4 will downmix correctly to 5.1, where a 7.1.2 downmix is unpredictable.
Knowing that most Home Entertainment setups are less than optimal, I am not sure why Dolby doesn’t see this as a potential issue.
(Thanks Erik!)
Fredo