Why bass management makes my life tedious

[Sancus]

Interesting. Do you mean on Home Ent or in the cinema? I think it would go over 115 (or rather, over 10dB above the peak level of the mains) if the bass management is done in the AVR and it has headroom in it. Meaning, the LFE can reach full scale and there's still headroom to sum in the BM on top.

Yes, it's my understanding that there is Home content like this, that can exceed 115dB when bass managed. This post earlier in the thread mentioned it, and I've heard of a couple specific examples cited before, perhaps in DTS 5.1, but I can't find them anymore

Considering cinema isn't usually bass managed it doesn't seem like the same problem would typically exist there.

 

[Chromatischism]

So if our current implementation of bass management is the problem, I wonder what sorts (if any) of mitigation strategies have been thought of?

It seems odd to me that we are duplicating bass content just by adding extra speakers. You'd think bass output should stay the same. There has to be a way to build some intelligence into these AVRs on this front, because we're widening the circle of confusion.

But I'm not completely confident that is really happening, either. Many people have noticed newer mixes have less low bass. Maybe there is overcompensation happening.

Either way, the way we are going about production and reproduction is clearly out of sync.

 

[Soundmixer]

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.

Actually, home mixes do not have fewer objects than theatrical mixes. Via Spatial encoding, all of the objects in the theatrical file are divided into clusters depending on the coordinates they represent in the sound field. On disc, you have up to 16 clusters that contain all of the objects in the theatrical mix. With data reduction techniques and spatial encoding, you can get them all on streaming platforms with as few as 12 clusters.

 

[Chromatischism]

Actually, home mixes do not have fewer objects than theatrical mixes. Via Spatial encoding, all of the objects in the theatrical file are divided into clusters depending on the coordinates they represent in the sound field. On disc, you have up to 16 clusters that contain all of the objects in the theatrical mix. With data reduction techniques and spatial encoding, you can get them all on streaming platforms with as few as 12 clusters.

Does the proliferation of soundbars affect mixing decisions at all? Do we all suffer because of the majority?

 

[Soundmixer]

Does the proliferation of soundbars affect mixing decisions at all? Do we all suffer because of the majority?

I can say with profoundly high confidence no. I (and those that do what I do in the industry) tweak a mix so it sounds the best it can when it leaves my studio. What happens in the field after that is the wild wild west and totally out of my control. I can tell you this - I have heard soundtracks I have mixed on a (supposedly) high-quality soundbar, and it sounded nothing like I heard in my studio.

 

[Chromatischism]

That's good to know. How about streaming services? Do they get their own mix?

 

[Sancus]

So if our current implementation of bass management is the problem, I wonder what sorts (if any) of mitigation strategies have been thought of?

It seems odd to me that we are duplicating bass content just by adding extra speakers. You'd think bass output should stay the same. There has to be a way to build some intelligence into these AVRs on this front, because we're widening the circle of confusion.

Well I wouldn't overstate the situation. At the end of the day, people are always going to set their own target curves to their preference, so there will be variation in amount of bass no matter what. And that's normal -- there is no one size fits all steady state room curve, only an average of preferences. At least film/streaming have some standards, unlike music which is the wild west.

Bass management is extremely important to managing room modes in domestic-sized rooms, so it is a benefit even if it causes some issues. That's not nearly the same problem in huge cinema rooms. I've been relatively happy with the results from most Atmos film mixes on my home system, though it is limited in output until I do some planned upgrades.

 

[audio2920]

So if our current implementation of bass management is the problem, I wonder what sorts (if any) of mitigation strategies have been thought of?

I guess that is what I've been saying, but to backpedal a bit, I don't mean that bass management is wrong exactly. It's just that we've got this mismatch between the -3dB pan law, the 20log (+6dB per doubling) electronic summing - hence the fact speaker count affects things - and we have to make one Atmos HE mix that will play nicely on a wider range of speaker counts than we ever had to before. Heck, in the old days a stereo mix could be played in mono resulting in compatibility issues exactly like this; it's just on steroids now.

BUT, to answer your question: There's quite a few patents and ideas floating about for "Intelligent Bass Management" I don't know if there's any solutions out there in the field yet? I've not knowingly heard one, but the detail in home AV equipment pushes a bit outside my knowledge area. They're all variations on a theme; trying to reduce the build-up from the summing of coherent sources being greater than the panning depth. I can't quite imagine this being any better, or rather any more predictable across more configs than simple LPF & sum solutions.

Dolby's solution is more simple and elegant, but only works for Atmos. I like it, I think. They call it "Object Bass Management" and it's kinda what it says on the tin. There's not much detail on it but it seems like rather than rendering full range signal to speaker positions and then folding the bass down to mono from there, they HPF/LFP each object before the HPF'd signals make their way on to the spatial renderer. This way, the bass summing is the same regardless of speaker count as it's upstream of the spatial positioning. I'm not sure it's a total solution, but on the surface it seems like it fixes a lot of things. However, right now, I'm really unclear on whether this is something intended for mass roll-out to the consumer kit...? I've only heard it in the studio renderer. But whadda I know, maybe they've done it already!?

Does the proliferation of soundbars affect mixing decisions at all? Do we all suffer because of the majority?

I'm totally with @Soundmixer on this. No one I know would make decisions specifically for soundbars.

I guess though, in line with my first paragraph rant above, while the existence of rubbish sound bars might not affect mix decisions directly, what probably does happen to some extent is we know (perhaps just subconsciously) that we are making a mix for everyone, and to that end, there is a certain restriction. If there wasn't, we wouldn't need an HE mix at all, we'd just put the cinema version out there and proclaim it to be perfect.

 

[audio2920]

It seems odd to me that we are duplicating bass content just by adding extra speakers. You'd think bass output should stay the same. There has to be a way to build some intelligence into these AVRs on this front, because we're widening the circle of confusion.

But I'm not completely confident that is really happening, either.

I should be clear that it obviously only applies when said bass is present in those extra speakers simultaneously.

So a lot of the time it doesn't happen. An explosion going off on-screen on the LCR, for example, won't be affected. However a sound that's spread around the room, like maybe a submarine ambience or drone, or crowd mics in a concert mix picking up the PA, will.

(The last example is actually a tricky one to deal with, because that bass can really help give a sense of scale, but it's probably got quite a lot of coherent information in it and, unlike an explosion where a few dB either way on the low end isn't gonna make or break a mix, a lifting of bass (and specifically the far-field wallowy stuff) in music is potentially more offensive, to my mind.)

 

[Spocko]

I guess though, in line with my first paragraph rant above, while the existence of rubbish sound bars might not affect mix decisions directly, what probably does happen to some extent is we know (perhaps just subconsciously) that we are making a mix for everyone, and to that end, there is a certain restriction. If there wasn't, we wouldn't need an HE mix at all, we'd just put the cinema version out there and proclaim it to be perfect.

Well this brings up an important point that I should've asked more pointedly: Other than the number of objects mentioned previously, what is the biggest difference between the original Atmos cinema mix and the mix intended for HE? And I know the answer starts with "depends" so let me provide the baseline assumption that we are talking reference HE playback system (I'm assuming 7.1.4?)

 

[audio2920]

Well this brings up an important point that I should've asked more pointedly: Other than the number of objects mentioned previously, what is the biggest difference between the original Atmos cinema mix and the mix intended for HE? And I know the answer starts with "depends" so let me provide the baseline assumption that we are talking reference HE playback system (I'm assuming 7.1.4?)

Depends

But, the biggest difference to my mind is levels. More specifically, dynamic range. While some people might be listening in a high end HT environment, the same mix has to sustain a lower listening level for a more casual listener. I'll mention now though, that some HE mixes are VERY similar to the cinema mix. If the delivery spec allows, and the original mix is quite controlled, it might play great pretty much as-is.

But let's assume we're starting with a cinema mix that's just too wild........

The most cardinal sin a mixer can commit is sending out a mix that's too dynamic and people have to reach for their volume controls to turn the loud scenes down / quiet scenes up. What they'll say, probably, is "I couldn't hear the dialog, the mixers don't know what they're doing and are making the dialog unintelligible. It's unacceptable." Of course the quality of the original recording and performance is probably the most important factor here, but having mushy dialog AND wide dynamic is the likely to cause negative feedback from the public.

So, dialog quality aside, part of that story is there will be an upper limit to how dynamic a mixer feels they can "get away with" without upsetting too many people. Although, each mixer will have slightly different personal preference for where they feel that limit is, and moreover, some films justifiably warrant a wider dynamic than others.

Moving on from mixer preference, the distributor's requirements may come in to play in determining the dynamic range. For example (for HE) Netflix request a certain measured dialog level and certain peak level. Although in Netflix's case the range is quite generous compared to others, and there's not too many criteria set, this will still dictate the maximum permissible range between dialog average and the loudest sfx/music.

I mention Netflix despite their relatively relaxed spec, as they make it more publicly available than most. Section 4.2.1 in this document describes those limits: https://drive.google.com/a/netflix.com/file/d/0B37xotBvlV3Qc1E4VW5sMzNwcmc/view?usp=sharing

But like I say, it's not uncommon to have tighter requirements than this, precluding the use of wide dynamics. Quite often the same mix goes on Blu-ray and VOD, even if the final encoding is higher bitrate on disc. I guess they base the spec on their target audience. Not for Atmos, but I know some US broadcasters are still requesting things to be done with no wider dynamic than old analog TV broadcasts, so while not totally relevant, it shows they feel this is appropriate for their listeners, and I don't necessarily disagree, even if it does feel very flat in the studio or a HT room.

Anyway, aside from getting the dynamics down, there's quite a lot of perhaps less noticeable (but cumulatively worthwhile) tweaks that go in to making an HE mix really work. A few things that might get tweaked as against the cinema mix are:

• EQ - brightness/boominess might be different on dialog
• Bass management - As per this thread it's brought in to play for the first time when the mix goes to the HE stage, do we need to redirect bass at all in the mix? Maybe.
• Ambiences might need lifting in quieter scenes
• Music might need lifting
• Surrounds from the bed play as point source in HE, so might need taming/diffusing if they're distracting

It's probably a very long list in reality, but that's the sort of thing... I probably do less HE than @Soundmixer though, who may have some more thoughts.

 

[Soundmixer]

Dolby's solution is more simple and elegant, but only works for Atmos. I like it, I think. They call it "Object Bass Management" and it's kinda what it says on the tin. There's not much detail on it but it seems like rather than rendering full range signal to speaker positions and then folding the bass down to mono from there, they HPF/LFP each object before the HPF'd signals make their way on to the spatial renderer. This way, the bass summing is the same regardless of speaker count as it's upstream of the spatial positioning. I'm not sure it's a total solution, but on the surface it seems like it fixes a lot of things.

You pretty much nailed it here. When you include the bass limiter function in the master suite, it keeps the bass from overloading the system.

 

[Soundmixer]

Depends

But, the biggest difference to my mind is levels. More specifically, dynamic range. While some people might be listening in a high end HT environment, the same mix has to sustain a lower listening level for a more casual listener. I'll mention now though, that some HE mixes are VERY similar to the cinema mix. If the delivery spec allows, and the original mix is quite controlled, it might play great pretty much as-is.

But let's assume we're starting with a cinema mix that's just too wild........

The most cardinal sin a mixer can commit is sending out a mix that's too dynamic and people have to reach for their volume controls to turn the loud scenes down / quiet scenes up. What they'll say, probably, is "I couldn't hear the dialog, the mixers don't know what they're doing and are making the dialog unintelligible. It's unacceptable." Of course the quality of the original recording and performance is probably the most important factor here, but having mushy dialog AND wide dynamic is the likely to cause negative feedback from the public.

So, dialog quality aside, part of that story is there will be an upper limit to how dynamic a mixer feels they can "get away with" without upsetting too many people. Although, each mixer will have slightly different personal preference for where they feel that limit is, and moreover, some films justifiably warrant a wider dynamic than others.

Moving on from mixer preference, the distributor's requirements may come in to play in determining the dynamic range. For example (for HE) Netflix request a certain measured dialog level and certain peak level. Although in Netflix's case the range is quite generous compared to others, and there's not too many criteria set, this will still dictate the maximum permissible range between dialog average and the loudest sfx/music.

I mention Netflix despite their relatively relaxed spec, as they make it more publicly available than most. Section 4.2.1 in this document describes those limits: https://drive.google.com/a/netflix.com/file/d/0B37xotBvlV3Qc1E4VW5sMzNwcmc/view?usp=sharing

But like I say, it's not uncommon to have tighter requirements than this, precluding the use of wide dynamics. Quite often the same mix goes on Blu-ray and VOD, even if the final encoding is higher bitrate on disc. I guess they base the spec on their target audience. Not for Atmos, but I know some US broadcasters are still requesting things to be done with no wider dynamic than old analog TV broadcasts, so while not totally relevant, it shows they feel this is appropriate for their listeners, and I don't necessarily disagree, even if it does feel very flat in the studio or a HT room.

Anyway, aside from getting the dynamics down, there's quite a lot of perhaps less noticeable (but cumulatively worthwhile) tweaks that go in to making an HE mix really work. A few things that might get tweaked as against the cinema mix are:

• EQ - brightness/boominess might be different on dialog
• Bass management - As per this thread it's brought in to play for the first time when the mix goes to the HE stage, do we need to redirect bass at all in the mix? Maybe.
• Ambiences might need lifting in quieter scenes
• Music might need lifting
• Surrounds from the bed play as point source in HE, so might need taming/diffusing if they're distracting

It's probably a very long list in reality, but that's the sort of thing... I probably do less HE than @Soundmixer though, who may have some more thoughts.

I think you just about covered it. We MAY also pull some objects (better known back in the day as sound effects) inwards in the mix (if they sound too far left or right) to keep the sound screen focused.

At the studio I work for, we basically create a mix for each format we have to deliver to. We stop trying to do a single mix deliverable when it was clear the public didn't like the end result. I agree with Audio2920 the biggest issue we face is getting the dynamic range under control. If you have ever heard a theatrical mix played in an HT, you would really hate it. You cannot just translate something created in a large space (the dubbing stage) and transfer it directly to a format designed for a smaller space. You have to customize.

 

[Soundmixer]

That's good to know. How about streaming services? Do they get their own mix?

Yes. Streaming presents all kinds of challenges when it comes to audio, so you could not use a mix designed for the disc on that platform.

 

[Chromatischism]

I should be clear that it obviously only applies when said bass is present in those extra speakers simultaneously.

So a lot of the time it doesn't happen. An explosion going off on-screen on the LCR, for example, won't be affected. However a sound that's spread around the room, like maybe a submarine ambience or drone, or crowd mics in a concert mix picking up the PA, will.

(The last example is actually a tricky one to deal with, because that bass can really help give a sense of scale, but it's probably got quite a lot of coherent information in it and, unlike an explosion where a few dB either way on the low end isn't gonna make or break a mix, a lifting of bass (and specifically the far-field wallowy stuff) in music is potentially more offensive, to my mind.)

It would seem logical that any reduction in the LFE channel to combat this should only happen momentarily as needed.

Or, for the HE mix, put that bass in the LFE channel to begin with and skip bass management where you have little control. That is backwards compatible starting now without waiting for more intelligent bass management schemes to come along. Sorry to anyone running speakers full-range – you should cut that out and buy a sub, anyway.

 

[audio2920]

It would seem logical that any reduction in the LFE channel to combat this should only happen momentarily as needed.

Or, for the HE mix, put that bass in the LFE channel to begin with and skip bass management where you have little control. That is backwards compatible starting now without waiting for more intelligent bass management schemes to come along. Sorry to anyone running speakers full-range – you should cut that out and buy a sub, anyway.

Absolutely. So, in the first instance I tend not to reduce the LFE itself when there's too much LF when we go HE. It just feels conceptually to me that the build-up is due to the mains, whereas the LFE is a discreet calibrated thing, and plays the same in HE and Theatrical until you start adding in the main channels. So, I'm more prone to finding ways of manipulating the other channels/objects instead (e.g. shelving, filtering, or crossing over stuff from the surround field). Now, I know I'm wrong about that - by very definition "build-up" is the sum of the parts - but it always seems to me that to mimic what we heard in the cinema, it's the summing of bass in the surround/screen channels that's new in HE, and wants tweaking. (That said, I do sometimes reduce the LFE a bit because of the 2.0 fold down needing bass in the mains - more on that below...)

Your second point is good, and I do agree to some extent. I've often thought it would be better to take control of bass management in the studio rather than leaving it to the end user. I sort of think it's too late to change it now though, it's just not how things have evolved. Actually, I once started doing exactly that on an HE conversion that was particularly problematic (i.e. chopping the mains and re-directing to LFE) but I bottled it half a day in... And here's some of the reasons why:

(1) I think it's unfair to assume everyone will want the crossover in the same place. We'd have to choose a standard, and it would need to be pretty high to allow for micro systems; maybe 250Hz or higher maybe? Some speaker positions and rooms just seem to work better at different frequencies to me. I'm sure you could science that out and find time/phase/EQ alignment to help crossover at a different frequency, but IMHO any given room setup will just lend itself to a certain x-over point better than others. (Again, that's just my opinion)

(2) As you pointed out, some people don't run with a sub.

(3) Although I wasn't going to admit it, I'm one of those who runs without BM for my living room I know, I know..... I do have a sub though. It just sounds nicer in that room, and I have less consistency issues with BM bypassed, even if it isn't as good scientifically. (This is on the verge of a "stereo bass" debate, but let's not go there )

(4) While we often do mixes for multiple formats (2.0 up to Atmos) there's less and less chance these days of the correct version tallying up through the distribution chain to the consumer. DD+JOC seems to be a pretty common way to distribute Atmos, which means to my mind, the Atmos mix needs to be as compatible as possible with everything from 2.0 upwards. If I remove LF from the mains, when the LFE gets discarded for the 2.0 fold down they'll be left with no bass at all. (The standard fold down removes the LFE.)

Now - if we could guarantee our channel based stereo mix went to everyone listening in 2.0 - or we could reliably change the 2.0 fold down to include LFE - and if we could enforce LFE feed to the mains for subless multichannel systems - I'd feel much better about your approach. But we can't guarantee any of those things, sadly... (People like me, in point (2), who like non-BM would just have to deal with, and I'd be OK with that)

 

[Spocko]

Depends

But, the biggest difference to my mind is levels. More specifically, dynamic range. While some people might be listening in a high end HT environment, the same mix has to sustain a lower listening level for a more casual listener. I'll mention now though, that some HE mixes are VERY similar to the cinema mix. If the delivery spec allows, and the original mix is quite controlled, it might play great pretty much as-is.

But let's assume we're starting with a cinema mix that's just too wild........

The most cardinal sin a mixer can commit is sending out a mix that's too dynamic and people have to reach for their volume controls to turn the loud scenes down / quiet scenes up. What they'll say, probably, is "I couldn't hear the dialog, the mixers don't know what they're doing and are making the dialog unintelligible. It's unacceptable." Of course the quality of the original recording and performance is probably the most important factor here, but having mushy dialog AND wide dynamic is the likely to cause negative feedback from the public.

So, dialog quality aside, part of that story is there will be an upper limit to how dynamic a mixer feels they can "get away with" without upsetting too many people. Although, each mixer will have slightly different personal preference for where they feel that limit is, and moreover, some films justifiably warrant a wider dynamic than others.

Moving on from mixer preference, the distributor's requirements may come in to play in determining the dynamic range. For example (for HE) Netflix request a certain measured dialog level and certain peak level. Although in Netflix's case the range is quite generous compared to others, and there's not too many criteria set, this will still dictate the maximum permissible range between dialog average and the loudest sfx/music.

I mention Netflix despite their relatively relaxed spec, as they make it more publicly available than most. Section 4.2.1 in this document describes those limits: https://drive.google.com/a/netflix.com/file/d/0B37xotBvlV3Qc1E4VW5sMzNwcmc/view?usp=sharing

But like I say, it's not uncommon to have tighter requirements than this, precluding the use of wide dynamics. Quite often the same mix goes on Blu-ray and VOD, even if the final encoding is higher bitrate on disc. I guess they base the spec on their target audience. Not for Atmos, but I know some US broadcasters are still requesting things to be done with no wider dynamic than old analog TV broadcasts, so while not totally relevant, it shows they feel this is appropriate for their listeners, and I don't necessarily disagree, even if it does feel very flat in the studio or a HT room.

Anyway, aside from getting the dynamics down, there's quite a lot of perhaps less noticeable (but cumulatively worthwhile) tweaks that go in to making an HE mix really work. A few things that might get tweaked as against the cinema mix are:

• EQ - brightness/boominess might be different on dialog
• Bass management - As per this thread it's brought in to play for the first time when the mix goes to the HE stage, do we need to redirect bass at all in the mix? Maybe.
• Ambiences might need lifting in quieter scenes
• Music might need lifting
• Surrounds from the bed play as point source in HE, so might need taming/diffusing if they're distracting

It's probably a very long list in reality, but that's the sort of thing... I probably do less HE than @Soundmixer though, who may have some more thoughts.

Wow, thanks for the information dense response. Essentially, the wider dynamic range intended for theaters may reduce dialogue intelligibility at home because during silent scenes when it's only dialogue, the HE user turns up the volume only to be blasted during action sequences. So you have to add compression while emphasizing the dialogue frequency range? This must be why AVRs have their own version of dynamic range compression for "late night watching" mode.

 

[kevinzzz]

Wow, this is fascinating - glad I stumbled on this thread. Thanks to our two pros for sharing their inside knowledge, and all for a lively discussion.

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.

This would have nothing to do with LFE though, right? This is just summation of LP'd content from the channels. However wouldn't Atmos include some inherent mitigation (pan law?) to reduce the disparity in the level of the full range channels if an object/channel was to be routed to multiuple channels based on how many speakers are defined in the decoder? Wouldn't that counteract this build-up?

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.

Is there always limiting happening in the HT side in the AVR? On the HT side I assume the BM happens after the signals exit the decoder, so it's really up to the implementation in the AVR (and the inherent limit of the speaker system I suppose) - wouldn't this be another stop betwen the 'chip' and the (even) wilder realm of room acoustics and calibration? I presume that you don't ride output limiters while mixing, so if a HT system had enough sub capacity, they should not experience this effect, right?

 

[Spocko]

You pretty much nailed it here. When you include the bass limiter function in the master suite, it keeps the bass from overloading the system.

I forgot to ask, when you're mixing to a "reference" HE playback system, what are your assumptions? for example, 5.1.4 or 7.1.4, LFE played full range because you're already adding LPF, etc. Understanding the mixer's assumptions will guide the HE enthusiast to be in alignment with the source material.

 

[Soundmixer]

I forgot to ask, when you're mixing to a "reference" HE playback system, what are your assumptions? for example, 5.1.4 or 7.1.4, LFE played full range because you're already adding LPF, etc. Understanding the mixer's assumptions will guide the HE enthusiast to be in alignment with the source material.

It is impossible to make any assumption because of the wide variety of reproduction sources in the field. Back in the day, there was a reasonable expectation that someone would have at least a 5.1 sound system of various configurations. Then it was 7.1. Now, there are immersive soundbars(which are huge sellers in the marketplace) 5.1.4 and 7.1.4 systems out there, so back to my statement "it is the wild wild west".

7.1.4 is the foundation of the Dolby Atmos suite, so that would be the foundational target - and you let the chips fall where they may after that. I would never assume the LFE is full range, because for the most part it is filtered at either 80hz or 120hz in the studio, and will be filtered again by the end-user in their AVR.