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Why bass management makes my life tedious

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@Soundmixer Please let me know when you're done editing your posts :) I probably better wait until tomorrow :)
Please let me know when you get the following information.

"we need to survey a decent amount of current recordings to make an authoritative statement one way or the other."

Until you do this, you are majoring in minors. And by the way, you have done your own fair share of editing, so the hypocritical nature of your comment is noted.
 
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Why did the engineer put full range content in the LFE there if it isn't meant to be played back at full range?
The LFE is a full-range channel until you engage an LPF on it. For music only, the LFE is not an LFE channel until you engage that LPF- it just another channel you can use in the mix - it is not needed to increase the dynamic range of the overall system.

Or are you saying that 'proper playback' of such LFE *is* full range? Good luck with consumers working that out.
If they don't work it out, they won't get the proper playback. With so few titles that do this, Let me advance you own words here.

"I own 85 surround music releases offering a lossless 5.1 option. More than a quarter of those (27) have full-band LFE (and some others have content that isn't full spectrum, but extends significantly beyond 120Hz). "
You own 85 surround mixes, and there are 6200+ SACD releases, 132 5.1 Bluray pure audio releases, and hundreds of concert videos on Bluray disc. When you have compared a larger sample size than you have presented here, please let me know. Context is everything, and you have not really provided any here.
 

krabapple

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The LFE is a full-range channel until you engage an LPF on it. For music only, the LFE is not an LFE channel until you engage that LPF- it just another channel you can use in the mix - it is not needed to increase the dynamic range of the overall system.
You're being pedantic yet somehow incoherent at the same time.. But I'll play along...leaving aside your vanishingly rare SACD height channel, what is the 'use' of an LFE channel populated with full-range content? Or for that matter, what's the use of LFE channel at all for music-only?

Saying 'engineers can do what they want' won't really advance anyone's knowledge on this point.


If they don't work it out, they won't get the proper playback. With so few titles that do this, Let me advance you own words here.


You own 85 surround mixes, and there are 6200+ SACD releases, 132 5.1 Bluray pure audio releases, and hundreds of concert videos on Bluray disc. When you have compared a larger sample size than you have presented here, please let me know. Context is everything, and you have not really provided any here.
Your perspective on the odds is interesting, especially as you don't know what releases are involved -- which surely impacts how likely a consumer of surround music is to encounter wideband LFE. 'Mainstream' artists/albums are more likely to be in collections that obscure ones. And guess what: my 85 releases are mostly by artists with names like Metallica, Bowie, Elton John, the Who, Yes, Rush, Van Morrison, Jimi Hendrix, King Crimson, Steely Dan, Pink Floyd. More than a quarter of them have full spectrum LFE (including at least one album by each of the artists I've just named).

And just to be clear, there's certainly more than 85 surround mixes in my collection -- but the rest are purely DD and DTS, so they tend to adhere to the use of a movie-like LPF for LFE. Or they're 4.0.
 
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krabapple

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Telarc did a few and a related application is utilized by mdg in their 2+2+2 recordings.
Thanks. THere;s a reason I hedged with mainly/only. "A few" by Telarc and occasional use by a niche German classical label still makes my point. The number of people who bought 'Dark Side of the Moon' or 'Electric Ladyland' or 'Tommy' in 5.1 probably dwarfs mdg's entire 2+2+2 catalog sales.
 

markus

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Please let me know when you get the following information.

"we need to survey a decent amount of current recordings to make an authoritative statement one way or the other."

Until you do this, you are majoring in minors. And by the way, you have done your own fair share of editing, so the hypocritical nature of your comment is noted.
It goes both ways. You don't present any evidence either. Until then I continue to recommend a LPF on the LFE. Better safe than sorry so to speak.
 
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You're being pedantic yet somehow incoherent at the same time.. But I'll play along...leaving aside your vanishingly rare SACD height channel, what is the 'use' of an LFE channel populated with full-range content? Or for that matter, what's the use of LFE channel at all for music-only?
You are being rather pedantic yourself, but let's move on to your question. I'll keep this short, there is no real use for the LFE in music PERIOD!

Saying 'engineers can do what they want' won't really advance anyone's knowledge on this point.
By saying they can do anything they want with the LFE, I just advance your knowledge. Your welcome!



Your perspective on the odds is interesting, especially as you don't know what releases are involved -- which surely impacts how likely a consumer of surround music is to encounter wideband LFE. 'Mainstream' artists/albums are more likely to be in collections that obscure ones. And guess what: my 85 releases are mostly by artists with names like Metallica, Bowie, Elton John, the Who, Yes, Rush, Van Morrison, Jimi Hendrix, King Crimson, Steely Dan, Pink Floyd. More than a quarter of them have full spectrum LFE (including at least one album by each of the artists I've just named).
In the grand scheme of things, none of this is relevant. My response to this is so what. There are 6200 SACDs, and you are complaining about 25% of 85. That is what I call majoring in minors.
 
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It goes both ways. You don't present any evidence either. Until then I continue to recommend a LPF on the LFE. Better safe than sorry so to speak.
Hey, it's your stuff. You can do anything you want with your stuff. I am not the one that needs to present evidence, I am not the one making assumptions and throwing crap at a wall - you are doing that. When you do that, the burden of proof is on you.
 
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Thread Starter #128
So, I feel @Soundmixer has been offering counterargument/disagreement with my initial statement. And, having thought about it, I think I am kinda wrong. Or rather, perhaps the slant I've presented to the issue is. (I do disagree on a few other minor details, but I'll circle back to those at the end of this post...)

Usually speakers are optimized in isolation. So the phase response between speakers doesn't match. The result at low frequencies is a bass response that isn't representative of the bass content in the recording whenever coherent bass content is present in multiple channels.
AND

He's not trying to account for unknowns. He's experiencing a level discrepancy between the recorded content and playback in his reference environment with/without bass management enabled and varying speaker counts.
This is exactly it.

And the reason for it is that two (or more) speaker won't play as fully coherent sources in most normal circumstances. Factors affecting how much they sum include, but are probably not limited to:

- The lower the frequencies sum more completely,
- The closer proximity the speakers the more they sum
- How absorbant the room's acoustic treatment at LF
- The size of the "mix position" / "sweet spot"
- The phase correction

Instead, we normally assume a doubling of speaker sources to add 3dB. This is in everything we do really, and it's an oversimplified assumption. Even in a basic stereo mix, we use a -3dB pan law. (Meaning, something panned hard left or right will modulate 3dB hotter on that single channel than if panned centrally and mod'ing on both.) In reality, some frequncies will be more additive in the room (up to 6dB) and other will be less; subtractive even, depending on listening position vs speaker locations, room reflections etc. But this -3dB pan law is everywhere.

A big part of this is the really simple physics that two point sources in a different location will have points of constructive and destructive interference. You can't phase optimise a usable listening area over the whole spectrum as the wavelengths are too short. This website's got the usual "two-point source" diagram showing this:

https://www.olympus-ims.com/pl/ndt-tutorials/intro/breif-history/

Of course, the lower the frequency, the less of an issue this becomes (or at least, the more correct-able it is with time/phase alignment within a small physical area), but it's still there. This is before you even take in to account the reflections.

In BM, there are no such "mathematical" summing imperfections. But does this mean bass management is better? It's just different. (which, is really what everyone's been saying here, I'm just a bit late to the party!) It's mono. It's mathematically perfect. But it's missing information. Two out of phase signals cancel out in a way they never would in a real space.

I think I've simplified and gone back to basics in my head about where I feel the discrepancy is, and it goes back to our -3dB pan law. In fact, I'd say the -3dB pan law IS the error. The discrepancy is very simply the difference between a -3dB pan law and a +6dB summing of phase coherent sound from 2 channels in BM.

So, I'll give an example:

1 channel = 80dB
Pan this to 2 channels via pan law = 77dB x2.
Sum these back together in to a mono and send to the LFE [(77)+(20log2)] = 83dB.

Meanwhile 77dB x2 above the BM frequency only sums back to around 80dB in the room. Maybe a bit more, but given the short wavelength, high unlikely to ever give 83.
Now extrapolate that out to 7.1.4 and the discrepancy gets wider.

This isn't exactly right as the levels are not what you'd measure - that would depends on how much content was above and below the BM filter - but the imbalance is the important bit.

the main channel limiter (to address bass build-up with BM), and an LFE limiter (to prevent overload of that channel while encoding the content). The specifics of how they all work together are not well understood, and I am sure Dolby wants it to stay that way (proprietary information?).
So, yes, information is limited and I don't know about the object limiting. However, I do feel that these (channel / LFE) limiters are nothing more than a "clip-stopper" on a per-speaker basis.

I believe the encoded object count to be 11+1(LFE) or 15+1(LFE) depending on use case. If you don't mod the LFE track you regain that as a spatial object. Difficult to prove, but it could be done I guess. This is neither here nor there really.

Regarding LFE with full-band content. I would say that, personally, I wouldn't intentionally let a mix go out with high frequency content in the LFE. It's just too risky regardless of negative effects, for me. As it goes, for film work, I tend to LPF the LFE at like 75Hz or lower (unless I really need the LFE a bit wider, in which case I'll just open up the LPF temporarily) which I guess accidentally goes a little way to reducing the discrepancy by it being re-filtered down the line. I may do things differently in music mixes, of which I've done a few but not loads. @Soundmixer appears to feel differently and personally I think that's fine. Both stances are justifiable and logical to my mind.

Doesn't the limiter kick in if you have like 100 FS objects in the DAW? Does it change with monitoring configuration, e.g. 5.1.2 instead of 7.1.4?

I'd like to find out because this would allow us to determine the worst case scenario. Most AVR manufacturers seem to apply their own bass management downstream of Dolby processing and I've found that they simply use a static headroom. Sometimes the headroom even shrinks when turning up the master volume control. Not a desirable situation.
Yes the renderer's limiter absolutely does kick in. And yes it changes with monitoring config - but only in the sense that you'll probably run out of headroom in 5.1.2 sooner than 7.1.4. More objects will get summed to the same "output" hole with lower speaker counts, so the limiter will grab more to keep it from clipping.

I think my point was more that, in the RMU (un-encoded Atmos) you can have 100 really loud objects and the limiter will work really hard. Once it's been encoded down to 12 spatial objects, I'm not sure they actually get truncated to 12 "full scale" objects at that point. My suspicion is they're stored with headroom (in floating point) and then limited at the decoder. I could easily be talking nonsense; I don't know....

If that's the case, the totally hypothetical worst case scenario without a limiter would insane. 118-ish objects all full scale, encoded down to 12 beyond full scale in FP, then summed down to a single channel....

And I agree, the last situation you describe is a bit crazy.
 

markus

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In fact, I'd say the -3dB pan law IS the error.
I agree. The better the room the closer we get to textbook summing of coherent sources though, i.e. 6dB instead of 3dB. As consumer room correction systems are getting better, the same trend can be seen.
 

krabapple

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In the grand scheme of things, none of this is relevant. My response to this is so what. There are 6200 SACDs, and you are complaining about 25% of 85. That is what I call majoring in minors.
:facepalm: Gee, it's like you didn't even read my response to that argument. I'll return the favor from here on. Because you can lead a horse to water....
 

markus

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:facepalm: Gee, it's like you didn't even read my response to that argument. I'll return the favor from here on. Because you can lead a horse to water....
More or less also my conclusion. You can't have a meaningful discussion with everyone all the time I guess.
 
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Regarding LFE with full-band content. I would say that, personally, I wouldn't intentionally let a mix go out with high frequency content in the LFE. It's just too risky regardless of negative effects, for me. As it goes, for film work, I tend to LPF the LFE at like 75Hz or lower (unless I really need the LFE a bit wider, in which case I'll just open up the LPF temporarily) which I guess accidentally goes a little way to reducing the discrepancy by it being re-filtered down the line. I may do things differently in music mixes, of which I've done a few but not loads. @Soundmixer appears to feel differently and personally I think that's fine. Both stances are justifiable and logical to my mind.
We both work on the film side of things, and we both use the LFE as it should be used within our industry. On that, I agree with you that an LPF should be used. If you were mixing in Atmos, the default for the LPF is 120hz, and basically, it has been that way since lossy Dolby digital days. The lossy DTS encoder uses an 80hz LPF, which has not changed with X.

I fully recognize that the music side does not really know what to do with the center channel or the .1 channel. Since they are not constrained by the rules (standards) of our industry, they can basically use it as they please....and on occasion they have. I have quite a few SACD's that didn't use the LFE OR the center channel (or both), and they have the freedom to make that artistic/technical choice. We don't have that option. As I stated repeatedly (without much cranial penetration I might add), you cannot use the film industry's standards to judge how the music industry chooses to use the multichannel format. Their goals are different than ours, and they quite frankly don't have any real standards to follow. I have been very clear and consistent about this point, and quite frankly I am the messenger. I have mixed quite a few film scores, but have never done a multichannel music mix for audio-only.


For movie sources, an LFE LPF is not necessary at the AVR level. The LFE is already low passed during encoding by default, and you actually have to turn it off (which is a purposeful thing to do) for it not to be used. For multichannel music sources, it can be used any way the audio engineer chooses, and the consumer should be aware of that. What choices they make are not up to me to explain, it is THEIR choices.
 

markus

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Not when one appears to have an agenda.......
You mean the evil, film industry crushing "use a LPF on LFE because there's recordings containing unwanted content out there"-agenda? :facepalm:
 
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You mean the evil, film industry crushing "use a LPF on LFE because there's recordings containing unwanted content out there"-agenda? :facepalm:
Can you please tell me what FILM has unwanted content in the LFE? Be specific here and name the title(s) and show the spectrograms. If you cannot do that, then maybe you should go back to the corner with your 3 piece KFC dinner. :rolleyes:
 
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Can you please tell me what FILM has unwanted content in the LFE? Be specific here and name the title(s) and show the spectrograms. If you cannot do that, then maybe you should go back to the corner with your 3 piece KFC dinner. :rolleyes:
Because you asked so nicely and respectfully:

BR-LFE-Jason-Bourne.jpg

BR-LFE-Jupiter-Ascending.jpg
 
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Two movies with a very brief spikes equal and industry-wide issue? :rolleyes:

Peter....stop cryin wolf.....:facepalm:

So now I suppose you will say these very weak spikes is actually audible. Please do that so I can laugh my butt off.
 
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Two movies with a very brief spikes equal and industry-wide issue? :rolleyes:

Peter....stop cryin wolf.....:facepalm:

So now I suppose you will say these very weak spikes is actually audible. Please do that so I can laugh my butt off.
Well, you wanted to see evidence. I provided it.

And no, it's not "very weak spikes". The graphs span the entire running time. LFE sounds in over 2 hours worth of data naturally show up as spikes. There is highly audible higher frequency content throughout the whole movie because no LPF was applied to the LFE. That's what the spectrograms show.

Everything else I'd like add to the topic has been said before and therefore I won't repeat it.

I have no interest in continuing this conversation with you as you've been nothing but disrespectful and ignorant towards the contributions of others. That's not how I want to spend my time here.
 

Sancus

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I see quite a lot of content in the 100-400hz range too which is definitely going to be localizable and probably sound weird in the typical case of somebody with just a single sub. Though I'm not sure why this conversation has spanned so many pages. The default 120hz LPF is no doubt in use in 99% of home theatres and if anybody adjusts it it's probably lowering it because they misunderstand the purpose.
 

edechamps

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the music industry is not bound to the film industry's standards. They can do whatever they want with the LFE.
This is very true and very unfortunate. Not only have I seen 5.1 music releases with full range content in the LFE channel, I've also seen plenty of releases that don't abide by the "+10 dB gain on playback" LFE convention used for movies, which means the LFE will play back way too loud on a system configured for HT. I am baffled as to why the multichannel music producers chose to ignore the well-established and well-defined movie standards. That makes it way harder to play their content correctly.

(I know nothing about the production side of things, but knowing what I know about the playback side, if I'm ever asked to produce 5.1 music, I know my first decision would be to ignore LFE altogether and keep it silent, leaving all the bass in the main channels. It's impossible to predict how the LFE channel will be rendered in a music playback system, which makes this channel a giant trap to be avoided at all costs. Leaving out LFE makes sense in music anyway, since "low frequency effects" seems like an awkward concept for that kind of content. It's not like you're going to have giant explosions in music.)

Going back to movies: as others have pointed out in this thread, I also personally experienced "garbage" (i.e. >200 Hz) content in movie LFE channels. It's rare, but it does happen, and for that reason I make sure the LFE is always lowpassed in one way or another in my playback system. I also came across content where the LFE channel was literally just a lowpassed mix of the main channels, which is technically fine but begs the question of whether the producer understands what LFE stands for.
 
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