1. For the most current home theater Atmos mixes, whether on disc or streaming, there is no definitive evidence that low frequency material found in theater releases have been artificially attenuated for the home despite countless posts elsewhere on the Internet. At worst, both theater and home releases are simply not as bass heavy as hoped, but there is no evidence that the original theater mixes have higher low frequency (below 80Hz) levels than the mixes intended for the home (disc/streaming). In other words if the track intended for a movie theater plays 18 Hz @105dB in Scene A then by golly this same Scene A when played at home (assuming reference setup with a capable subwoofer) will also play 18 Hz @105dB without any additional filtering to "recover lost information".
This is the most complex aspect, to which a definitive answer is difficult. But, in short I think it fair to say that most home entertainment (HE) mixes don't intentionally have
relative reduced bass content compared to the theatrical. However, is 18Hz @ 105dB in the theatrical mix 105dB in the HE? No, probably not, mostly because of normalisation, phase relationship with main speakers, and mix adjustments deemed necessary for HE.
To elaborate on that though:
[1] I no longer believe a reference level exists for Home Entertainment. I say this because 90% of the time we are given delivery spec which requires an average loudness normalisation NOT a reference level for mixing and replay. This is inherited from broadcast of course, and sometimes bluray mixes are still done at reference, but often not. Certainly anything on a streaming service will be normalised (and thus de-referenced, if you will) and I can't see how a home theater listener could ever know what level would correspond to the mixed level.
An example of what this normalisation might do could be: Let's say we don't want to adjust the theatrical mix AT ALL, we just want to put it out for home use, as-is (This isn't what happens, but just for simplicity!!)
Mix of film "A" comes in 3dB louder than spec, so we turn it down 3dB. We'd now need to set our monitors to 88dB* to get it replay as-mixed theatrically.
Mix of film "B" comes in 4dB quieter than spec, so we turn it up 4dB. We'd now need to set our monitors to 81dB* to get it to replay as-mixed theatrically.
*Assuming 85dB is ref.
[2] The dynamics of the theatrical mix may be deemed too wide for home use, and it may be reduced for HE.
[3] Because there's no bass-management in theatrical, 115dB is always available for LFE content. In Atmos HE, that "LFE" output will be limited to the same level BUT it also contains the bass-managed signal from the main channels, which (in Atmos at least) then gets limited back down to that maximum output level. If the BM from the screen channels pushes the LF output channel 6dB over saturation, the limiter will pull 6dB off your 105dB 18Hz tone in the LFE along with everything else (See point 4)
[4] Not directly relevant to a single 18Hz tone on the LFE, but...... As discussed earlier, the number of speakers in the replay system can have an effect on the spectral balance when bass is omnipresent (or multipresent, not sure what the word is??) basically when bass emanating from multiple speakers has a mostly positive phase relationship. This then sums in with LFE so, at low level you might find a 5.1.2 system plays with less bass overall than a 7.1.4 system because less speakers are summing together in the bass management. Conversely, as the level increases to the loudest points, you might hit the LF output limiter, and a 9.1.6 system is more prone to this than a 5.1.2 system.... So, spectral balance (pivoting around the bass management frequency) is, in my opinion, a little bit unwieldy** even before the sound leaves the Atmos decoder "chip" and gets in to the perhaps even wilder west of room acoustics and calibration.
(I actually hope to provide some demo Atmos content at some point in a few weeks to illustrate this last point.)
- Follow up question for @audio2920 who mixes for the theater release: is there any truth to the rumor that modern movies have lowered their LF levels significantly compared to movies made 20 years ago to reduce the amount of bass leakage into adjacent theaters because most theaters today are densely packed multi-plex theaters?
I definitely think multiplexes are guilty of reducing the LFE level for this reason, and perhaps because they don't have the required headroom and/or ended up blowing drivers in their LFE stacks. But mix-wise, no.
2. Additionally, despite home mixes having less objects than theater mixes and other data bandwidth differences, this disparity does not affect the low frequency levels intended for the LFE.
Correct, the number of objects doesn't really affect it in most circumstances. The LFE remains discreet and utilises an object when LFE content is present, as I understand it (but, I'm not an expert on the spatial coding used to reduce the object count!). As above, it's more about how the discreet LFE interacts with bass management, in my opinion.
3. Lastly, it is not common knowledge (at least I didn't know this!) that the LFE has an LPF encoded into the home mix so it's best to let your AVR or processor treat the LFE as full range rather than add any additional LPF filtering to it - filter the LFE only if you notice localization artifacts or noisy artifacts coming from your subwoofer in a badly mixed release; but this should be the exception not the rule, because we are assuming that most home releases are mixed with LPF properly encoded. And even in this worse case mix, your main speakers will likely mask the noise due to the huge dB difference.
I think this was a point
@Soundmixer was making, but I agree with it. There should be no need to LPF the LFE again.
