r/DolbyAtmosContent • u/HM_Bert • 22h ago
discussion Looking for advice before I go down an LFE phase rabbit hole:
Hey, so I have a 5.1 system ran via a MiniDSP Flex HT processor, and I've been getting frustrated by the LFE channel in Atmos songs seemingly being out of phase at certain bass frequencies.
I made a post about this before but I didn't go very in depth, and just decided it was best to disable the LFE and just listen to the bass in the main channels, which 99% of the time matches that of the stereo mix, with expected bass balance from low to high.
See here regarding 2nd pic: https://www.reddit.com/r/DolbyAtmosContent/comments/1w7fqge/the_lfe_is_out_of_phase_and_causing_cancellation/
However I've been experimenting with turning the LFE back on, as it does just feel wrong potentially missing out on creative intent, and almost just out of principle because it should be working, and many people don't even have the option to disable the LFE on lower end processors.
The thing is that is this problem occurs *so often*, in both Western Pop and Korean pop content, by different immersive mixers.
Although it's certainly possible, I really hope that it's not the case that so many mixers in multi-million studios labels etc (Many which are visited by and certified by Dolby) are screwing up the LFE phase relationship, and that there's instead something strange instead going on at my end I've been missing.
Now, when I measure with timing reference my LFE and bass managed L R or C channel, then use the alignment tool, they pretty much sum up perfectly (certainly at low frequencies, which is where I'm experiencing the cancellation). So again it would seem that the problem is the content, not my end, but still I have to get to the bottom of this with certainty for my own sanity.
From what I understand, REW uses a fixed channel order regardless of outputting via USB or HDMI, but I may as well test with HDMI audio instead of USB which is what I normally do.
So I've been thinking of every possible combination I can test to ensure things are working as they should:
- Bass Management with LPF and HPF, with LFE with LPF (as is currently the case, and the recommendation from MiniDSP in their guide)
- Bass management with LPF and HPF, LFE without LPF
- Bass management with LPF and HPF, inverted LFE
- No bass management, full range signal + LFE
- No bass management, full range signal + inverted LFE
- Bass management with HPF done in the speaker EQ instead of bass management channel
- Disabling all processing possible and recording the channels into my PC via a focusrite interface and comparing the phase in a DAW
I am also planning on checking not just the loads of songs I know have problems, but also some films, which perhaps have less likelihood of the LFE being badly mixed? (No guarantee though)
For example this moment in Dune https://youtu.be/26bgYpJOqcw?t=476 where there is a simple bass sweep down to ~25hz with little harmonics or other noises, which is in the 2.0, but presumably also in the LFE as well, could hopefully be easy to compare.
However I know there's some folks here with access to actual production and viewer software, and if they'd be able to extract or record files and see how the LFE on the summing is on at raw digital level is without any of the extra stages in the way, that would be super appreciated. Or just any advice on other things I can check and may have missed, thank you!