Originally Posted by PSBMAN
If you are running an HDMI from the Oppo Out to the TV and using the other Oppo HDMI out to the bar for sound, you would switch secondary audio to on correct ?
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NOPE! Secondary Audio, despite the name, has nothing to do with the 2nd, Audio HDMI output.
Secondary Audio refers to an extra, Stereo, sound track present on the disc that can be mixed on top of the feature audio track. This is something that only exists on Blu-ray and UHD discs. Disc authors use it for things like disc menu sound effects and certain picture in picture commentary tracks.
You have to use Bitstream output to play Atmos *AS* Atmos. But if you also have Secondary Audio ON, and if the disc also has Secondary Audio authored anywhere on it (even if you have *NOT* selected to play a disc feature that actually uses that Secondary Audio) the decoding rules for Blu-ray and UHD discs work like this:
1) The Bitstream track is decoded into LPCM (whether or not you've actually selected to play a disc feature that uses the Secondary Audio)
2) The Stereo Secondary Audio, if actually present for what you are playing, gets mixed into that multi-channel LPCM
3) The result gets converted BACK into a Bitstream for output
But no consumer gear has the horsepower to do step (3) in real time to produce a LOSSLESS Bitstream track. You get a LOSSY Bitstream instead. So what you get for the re-encode back into Bitstream is no longer an Atmos track.
(In the case of the OPPO, what you get is the highest bit-rate form of "lossy" Dolby Digital 5.1.)
Again, the certification testing for licensing for these discs requires all this.
The bottom line is that if you use Bitstream output with Secondary Audio ON while playing an Atmos track -- and if the disc has Secondary Audio authored ANYWHERE on it, even if you've NOT selected to play that Secondary Audio -- then what you get for the Bitstream output is *NOT* Atmos. It's not even Dolby TrueHD 7.1. It's DD 5.1
When you press and release the Info button while playing the movie, the left hand side of the bottom line of the Info display tells you what's being played off the disc for Audio. (For an Atmos track, that will read TrueHD 7.1.) Just to the left of that is a mysterious icon. If that icon looks like a few overlapping discs, then Secondary Audio processing is not engaged. If it looks like a wavy line, then Secondary Audio *IS* engaged, and the Bitstream output will be DD 5.1 (for an Atmos track) and the Atmos nature of the audio will be lost.
If you are using Analog audio output or HDMI LPCM audio output, it is OK to leave Secondary Audio ON all the time. The player does steps (1) and (2) above in a way that preserves the full quality of the feature audio track -- including channels up to 7.1 and sample rate up to 192kHz.
The difference is that the player does not have to do step (3) -- the re-conversion BACK into Bitstream for HDMI output.
But playing an Atmos or DTS:X track *AS* Atmos or DTS:X requires use of HDMI Bitstream output (into an AVR that knows how to process those).