This is a really interesting conversation to see. I have some opinions that I hope are helpful.
Major labels, Dolby, and Apple seemingly use film-based standards for music. Not sure why... As such, Lo/Ro is the standard that is pushed and it makes me sad to hear Dolby Atmos mixes downmix in real world listening scenarios in was that or not-as-intended. Because Lo/Ro folddowns don't do Atmos music mixes justice, the current standard practice for most mixers is to make a complete stereo mix first then derive the Atmos mix from stems of the stereo mix. Kind of silly to me and ultimately results in highly boring Atmos mixes (stereo mix in the front with some reverb everywhere else) and/or wildly different sounding, inconstant mixes all together... You CAN get excellent Atmos mixes this way too but ultimately you don't have a surround compatible "stereo" mix.
For those who care, I am an LtRt advocate for music. It's a preference and not a mandate. Also, even though I mix everything in surround myself, I also don't believe that everything should be mixed in surround sound. Also, LoRo seems to work quite well for film to me.
My approach is to use the
QUARK flavor of LtRt/regular matrix/QS/dlp2/involve for all of my mixes. The encode is made from a 4.0 fold down of the Atmos using downmix settings
not enforced by the major labels:
- All trims are "manual" at 0dB to ensure proper fold downs for music. (which fortunately seems to finally be taking hold with most professionals)
- 5.1 down mix using "Direct render with room balance." (not common)
- 5.1 to 2.0 down mix using "Lt/Rt (Dolby Pro Logic II w/Phase 90."(not common)
- Because the Dolby Atmos Renderer doesn't export a 4.0 file, I derive this from a 5.1 export.
I find that these settings most consistently maintain the integrity of my mixes in various waterfall of down mix playback scenarios.
With this said, there are are a lot of pitfalls to listen for including the fact that the Atmos object front to back "0" (center) position is actually surround rear in 5.1 also, when using LtRt and playing back the fold down in mono, anything in the rear surround center phase cancels with LtRt encoding. Another reason why many mixers poo-poo LtRt is the phasey sound of anything in the rear. Depending on the music, I actually like the sound of it since that phasy sound is the psychoacoustic effect of something playing in the rear (kind of the point). With that said, it can get out of hand and is some of the reason why people just send everything below 120Hz to the LFE (which I do not encourage blindly doing).
I use a couple of tricks to solve these issues which were very difficult to accomplish back in the quad-era 70s or even LtRt "2000s" era. There is lots to listen for but here are a few helpful techniques:
- The FREE Izotope Ozone Imager helps a lot with the rear-center mono phase canceling.
- To help with the phasieness, I'll sometimes bandpass the low end of the rear channels to the front channels and this tightens things up a lot. Kind of like thing of sending the low end to the LFE but with more control, in my opinion.
- For the center channel, because of what the "dialog enhancement" processing that nearly every playback system does to music I generally keep my Atmos objects away from the front center and use a phantom center instead when I want something to sound like it's coming out of the center.
In summary, I listen to my mixes in a lot of different scenarios and there are creative compromises to make for a consistent listening experience from Atmos all the way down to mono.
