When I tested the Atmos files, there were 4 different kinds. Did you try each kind?
IAA confirmed for me that at least one type is lossless. Can't remember which.
I confirm the FLAC 5.1 is clearer and sharper than both Atmos mix (see below). BUT it is important to consider that they are 'different' mixes.
In the FLAC 5.1 the voice is also more impacting, sharper and mixed at higher volume than in Atmos. FLAC 5.1 has a global higher volume than Atmos. When trying to level match, the difference lessens, but I can still hear the FLAC cleaner.
The mixes are different. You don’t hear the sounds and voice at the same locations (apart from 'downlocate' tops to floors). I like more the spatiality of Atmos, but really the FLAC sound quality is superior.
My downloaded files from IAA are five kinds. (All MP4 containers except FLAC):
ac-4 (Unable to play this codec neither in PC nor Dune or Oppo 203). I assume this is the Stereo version, but as AC-4 may contain objects, who knows...)
2.0 16/48 kHz
dmix (Dolby Digital Plus) (Seems to be the same Atmos mix downmixed to 5.1, i.e. the same core mix without the Atmos objects). It is different mix than the FLAC 5.1
E-AC-3 5.1 16/48kHz
FLAC 5.1
5.1
24/96kHz
joc_448 (Dolby Digital Plus with Dolby Atmos)
E-AC-3 JOC 5.1 16/48kHz bitrate=448 kb/s
joc_768 (Dolby Digital Plus with Dolby Atmos)
E-AC-3 JOC 5.1 16/48kHz bitrate=
768 kb/s
So,
the only lossless is FLAC 5.1 and in Hi-Res. Both Atmos sound almost the same to me. No too much difference because of the the bitrate.
I wonder if the Blu-ray, presumably in TrueHD Atmos,
will sound some better than this DD+ Atmos. If the mix/master is the same perhaps there would not be much difference.
Anyone with both copies to compare?