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Why bass management makes my life tedious

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#1
I'd like to talk a bit about one problem (amongst many) I find when mixing films in surround sound: Bass summing.

It's not a new problem, but as speaker counts have gone up, it's definitely been exacerbated. While the issue is kinda multidimensional, discrepancies in bass level at the point of replay exist partially because of the interaction between:

- Bass management.
- Lack of bass management.
- Speaker coupling / summing in the acoustic domain.

The amount of bass extension (how low the system can go) obviously has an effect too, but I find that less disruptive to the experience than multiple decibel level differences in the 40 to 100Hz range which come about through bass management or lack thereof.

In cinema (theatrical) mixing we don't have to worry about bass management much. The screen channels only go down to around 40Hz, but ya know, so be it. We can dump to the LFE if we need to. In general, the translation room-to-room is decent in regard to "bass summing" as everything stays discreet. Each channel we had in the mix exists as a physical speaker location except for surrounds in Atmos. Sure, sometimes the screen channel speakers couple to each other differently in different rooms, but it doesn't affect things too much.

However, when we move out of that world and into Home Entertainment, things get difficult. The big unknowns are (a) Will they have bass management, and what frequency will they crossover? (b) How many speakers will they have?

The reason these questions matter is that the way low frequency content sums in bass management is different from how it sums in the room. This is because, as most people on this forum will know, in general bass management involves making a mono signal path and slamming together all the "speaker" signals below a certain frequency. In room, the summing is dependent on a few things, but generally the screen channels have more coupling to each other than they do to the surrounds. In all cases though, summing in the signal processor of fully phase coherent material from multiple speakers will result in a level push of [20log(number of speakers)] so 6dB for each doubling of sources. The acoustic summing will be less than this.

At the other end of the scale, if I ran a 40Hz signal 180 degrees out of phase into the left/right pair, someone who's totally in to their bass management region at that frequency would get literally SILENCE as a result of that signal. Without bass management, you'd get a wide stereo bass effect.

Because low frequency content is generally quite coherent across channels (unless the mixer has done something deliberately that isn't, or it's music recorded on a large stage with mics a great distance apart) using bass management therefore in general gives more bass push to a mix as a whole than allowing the main speakers to run full range.

Assuming the consumer is using "speaker based" bass management, the more speakers they have, the bigger the LF push compared to the unmanaged version UNLESS there's only ever "bass" in one speaker at a time in the mix. Now, this is possible. I could brutally brickwall chop all speakers off at 160Hz and put everything below that into the centre channel. (side note: I can't put that content in the ".1" as in most default stereo downmixes the decoder mutes that off, so anyone listening via a 2.0 decode would have no bass at all.) I'm not seriously suggesting this as a solution but it's about the only thing that would be an absolute fix for the issue rather than the fudges we end up doing in the real world.

What I'm talking about here is of course just the basic "maths" at the decoder/bass management stage, so it's all before you even get the signal as a far as "preference" curves on the consumer's line-up, which in some cases compound the error by having more bass tilt-up than studios. Despite personal preference for spectral balance between Re-recording Mixers being relatively similar in my experience, this bass management issue means that mix-to-mix, a consumer will probably find some mixes have loads of LF lumping up and others don't. If you don't use bass management, things might be more consistent from film to film, EXCEPT the mixers have to take in to account that most, but not all, people are bass managing and have to compromise the mix accordingly. And, there's no standards for this yet.

Now, I'm not against bass management. It probably does more good than it does harm. It's just that it's implementation is so unpredictable right now all I can do is try my Home Entertainment mixes without bass management, and bass managed at a random frequency on an random number of speakers (probably 7.1.4 since that's what the clients usually wants it mixed on) and then make compromises to the mix such that neither experience sounds terrible. Generally this means if the bass managed replay gets too LF prominent anywhere, my options are (a) finding some way of de-correlating the offending signal, (b) re-distributing the LF content to a smaller number of speakers or (c) reducing the LF content to bring it back in to the realm of acceptability. The last option (c) being either as a whole sound element if it's an object in Atmos, or by dipping the LF content in some of the speakers if it's a channel-based surround recording.

Help is at hand in the form of "OBJECT BASS MANAGEMENT" in Atmos. This removes the "number of speakers" variable so it's a step in the right direction. So far as I'm aware, not many people are using this in the consumer field yet? Please correct me if I'm wrong.

For your amusement, here's what happened in my mid-field studio with and without bass management, when playing phase coherent filtered pink noise, measuring with a single mic at the mix position. (This was a couple of years ago and I've lost the details of the pink noise but it wasn't heavily sub-sonic. Maybe rolled off 12dB/Oct @ 40 & 180Hz or something and the bass management would have been around 80 or 100Hz).

ACOUSTIC SUMMING (dB) / BASS MANAGED (dB)

L = 74.0 / 74.0
L+R = 77.9 / 80.0
L+C = 79.4 / 80.1
L+C+R = 82.2 / 83.5
LS+RS = 77.2 / untested
L+C+R+LS+RS = 85.1 / 88.1

As you can see, this test only spanned up to 5.0, but as the speaker count increases, so does the discrepancy. By the time you're in 7.1.4 or 9.1.6 the difference is really quite large. Maybe I'll run a real world test of that if I get time...

Other things of note on those numbers, you can see the Left & Centre couple more in this frequency range than the Left & Right, but that's a whole world of room calibration pain that few people venture in to :p I don't have those monitors any more or remember much about the calibration, but you can see that the single left speaker playing on it's own was bass managed accurately in level at least. I suspect the whole room was time aligned with some reasonable degree of accuracy to the centre channel. The FR of each speaker probably adjusted individually rather than summed.

/Rant
 
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#2
However, when we move out of that world and into Home Entertainment, things get difficult. The big unknowns are (a) Will they have bass management, and what frequency will they crossover? (b) How many speakers will they have?

THX has done a terrific job at defining standards for home theater mixes via their PM3 certification for studios, and for the most part, the industry has embraced those standards for the home. As we have gone beyond 5.1 and 7.1, Dolby has set the standards for immersive audio, which extends beyond 5.1 and 7.1 for HT. Beyond those standards, it is the wild wild west when it comes to playback results.


Because of the many issues with directly importing cinema mixes directly to home media, The studio I work for decided that they would create mixes specifically for the HT environment. This way we could create a special mix that translated well from a theatrical printmaster to the home environment. Shortly after we did it, Sony followed, and other studios did as well with their premium titles.

My experience has been that you must create a great mix on a defined standard, and let the chips fall where they may after that. There is no way in hell you can create a mix that works well outside that standard, the variables are all over the place.
 
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#3
I had a question for both of you @audio2920 @Soundmixer on this, it came up regarding the X-Curve discussion. Are all of the major studios doing specific "home" mixes? Does that require multiple mixes and remastering (streaming mix, Blueray mix)?

This is a blurb from Denon site (one I picked at random that has a feature to kill the "brightness" of movie sound mixes):

"Cinema EQ and THX Re-equalization® share a common goal as they’re both designed to remove excessive high frequency information from movie soundtracks optimized for theatrical presentation."

I'm assuming that HT Receiver makers have such preset eq features is there is content, a fair amount of it, that wasn't re-mastered for HT environment?
 

audiofooled

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#4
Likewise, a question for both @audio2920 and @Soundmixer , why are small firearms shots in action movies so exaggerated, not so much in loudness but in frequency range? IMO, a bit surreal if it sounds more like a cannon blast rather than a simple pistol.
For example what ever John Wick has in his hands digs deep down sometimes to 35 Hz or so, and up to about 110, summed to be perceived as quick and instantaneous? This on a capable system of course results in a viewer "being shot" in the chest. By the end of the movie with thousands of gunshots and explosions, I get pretty beat up and end up ever decreasing the volume, even double attenuated than at the beginning. To me it can get too much.
Decreasing the bass only was never a solution because upper bass is gone also and attenuating the LFE only levels out so that every explosion and gunshot sounds too similar...
Is this a part of the problem @audio2920 suggests? Or is it mixing as such for targeting wide range of systems with different low frequency extension capabilities, so the ones that dig down low wouldn't mind after all, and others not so capable would still get a satisfying "experience"? Personally, it can be quite shocking when after a quiet dialogue suddenly you get blasted out of nowhere...
 
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Thread Starter #5
Because of the many issues with directly importing cinema mixes directly to home media, The studio I work for decided that they would create mixes specifically for the HT environment. This way we could create a special mix that translated well from a theatrical printmaster to the home environment. Shortly after we did it, Sony followed, and other studios did as well with their premium titles.
Sorry, maybe what I wrote was misleading. I mentioned theatrical mixing but I was only trying to convey that it's quite normal for film mixes to start their life in a big room, not that we send these out. From that point on I'm only referring to specific HE mixes. Although, frustratingly it's not as rare as one might hope that the wrong mix version gets used...

My experience has been that you must create a great mix on a defined standard, and let the chips fall where they may after that. There is no way in hell you can create a mix that works well outside that standard, the variables are all over the place.
There are indeed tons of variables and generally I think it true that "you can only mix to the room you're in" kinda thing. You can't predict what someone else will do to it. Except, you kinda can to some extent on the downmixing and BM front.

I also agree with you about standards, but do feel that what I'm talking about here is not replay outside "the standard" but within it. The standard for Atmos HE replay is 2.0 up to 9.1.6 and beyond. Mixing HE in Dolby certified room in 7.1.4 with BM @ 80Hz may be a standard; it's a good starting point, and it's impossible to cover everything in the time we have to do an HE mix. But I feel like this issue, particularly in immersive mixes, could benefit from more attention than it currently gets.

I used to be of the mindset that if someone played (for example) a 5.1 HE mix downmixed to stereo and it sounds a bit different to how the director/mixer intended, that's on them. "Play it in 5.1 in a calibrated room if you want to hear it correctly," I thought. But I guess now with so many permutations of speaker configs, my attitude to doing a mix and "letting the chips fall" (great way to describe it btw!) has softened slightly in the sense that I feel more responsibility than ever to make a single HE mix play nicely on a wide range of systems. This is because it's just the DD+JOC that is going to be streamed in a lot of cases, more so as the years roll by. Applying my old logic, that would mean everyone with Atmos HE required precisely 7.1.4 with an 80Hz BM filter to get the mix out of the decoder "correctly" and that's just not how it works any more.

Now, for all my "complaining," most of the time it's a non-issue. Most things it affects are transient in nature (transient in the sense they're there for a moment then they're gone) so a few dB either way on some of these things isn't going to make or break a mix. But there are times when there's LF flying all over the place [maybe on a submarine, or a music gig with crowd mics in the surround field, or a helicopter interior?] and in 5.1 native HE mix the difference between BM or not was only a few dB at worst. But now, if you're unlucky with how the phase lands, someone playing that Atmos Blu-ray in a 9.1.6 BM'd room could have like 10dB more bass* than someone playing the same track in like a 5.1 non-BM'd room, even if both rooms are calibrated perfectly to the same standard. This is significant to my mind. If your DAC had a 10dB error in it you'd be pretty upset, but yet the output from an Atmos mix decode+BM strategy can have errors this large.

(*I've not math'sed that out and it's content dependant.)

To be clear, I'm not talking about checking the mix on a ton of systems to check minor differences in the presentation. Obviously we can't make it absolutely work in consumer's room - as you say, the variables are all over the place - I just think we should do our best to get it as far as the decoder output without major discrepancies in level or spectral content being introduced by downmixing and/or BM. It'll never be perfect, and as you rightly say, if it's a good mix to begin with, it will hopefully still stand up in the real world.

Moreover, I would love it if someone (Dolby) would roll out a system where I didn't feel I had to think about it :)
 
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Thread Starter #6
I had a question for both of you @audio2920 @Soundmixer on this, it came up regarding the X-Curve discussion. Are all of the major studios doing specific "home" mixes?
Yes, absolutely. I would describe most of the process as re-mastering rather than re-mixing, but there will likely be adjustment of balance between elements in some areas.

Does that require multiple mixes and remastering (streaming mix, Blueray mix)?
The short answer is "yes."

In reality every film is different in it's requirements. I would say that most people's approach is usually to take the theatrical mix and manipulate it in to an HE mix, starting in the widest dynamic and channel count format the client wants - so maybe Atmos for Blu-Ray. Having done that, you've got a mix that works better in mid-field monitoring and you can deliver for that format. You'll likely then take that as a starting point for the next version down the line; maybe VOD. And then use the VOD mix as a starting point to make a broadcast TV mix. It's not always done this way, but it's the most time efficient.

Sometimes these mixes are pretty similar, but usually we're working to a bunch of different loudness requirements and limits for the different distribution channels, as well as the studio's archive. So, a deliverable we send for a streaming service will probably have more dynamics than one we send to a terrestrial TV network.

Side note, these specifications change often. So there isn't really such a thing as "reference level" for Home Ent. A mix from 2015 could be a different level and dynamic from 2021 even if it's through the same distribution channels.

I'm assuming that HT Receiver makers have such preset eq features is there is content, a fair amount of it, that wasn't re-mastered for HT environment?
I'm not sure of this, but your logic certainly makes sense. Going back to the early 90s and earlier, TV mixes were often derived from the SVA, which is a stereo mix on the 35mm optical print. The dynamic of this isn't as wide as a digital track so it wasn't so far out of spec for TV to begin with. Although not pretty, it wasn't totally unusual for this to just get "limited" to make it broadcast legal and off it went. This wouldn't even necessarily be done by a re-recording mixer, it might happen in a video tape transfer bay where someone just spot checked it wasn't broken on some 19" rack speakers.

Even in the mid to late-90s when were getting in to 5.1 HE mixes for DVD, it took a while for everyone to get their heads around it, so they probably didn't get the same treatment as they would today, but the bigger productions probably got on board sooner than the lower budget ones. So, I'd say for content up until the early 2000s it's possible it didn't get much Home Ent love from the mixers at the time. Much of this will have been revisited since.

Today, perhaps those settings exist as preference thing for people who find they want more HF for lower level listening, even on modern home mixes? Kinda like the "loudness" button an 1970s amplifier. We do monitor the Home Ent mixes at a lower level than theatrical of course, but it's almost certainly still hotter than most people will listen at home.
 
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Thread Starter #7
I realise I'm perhaps making a bigger deal out of this than it is most of the time. But, I honestly feel this BM issue could have a lot to do with people complaining about "muddy" mixes etc. Far more so than x-curves and general EQ considerations.

I mean, my own front room system isn't even FR corrected. It's just some speakers levelled and crudely time corrected, and I have no issue with listening to that.
 

FrantzM

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#8
Getting the bass right in MCH/Movies is to me at least, frustrating. I let Audssey do its things, trim it a bit and watch the movies. I am less critical of the sound once the dialog is good.

I have come to think of having a separate 2-Channel system or in my current location, A 2-Channel with HT bypass...
 
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Thread Starter #9
Likewise, a question for both @audio2920 and @Soundmixer , why are small firearms shots in action movies so exaggerated, not so much in loudness but in frequency range? IMO, a bit surreal if it sounds more like a cannon blast rather than a simple pistol.
For example what ever John Wick has in his hands digs deep down sometimes to 35 Hz or so, and up to about 110, summed to be perceived as quick and instantaneous? This on a capable system of course results in a viewer "being shot" in the chest. By the end of the movie with thousands of gunshots and explosions, I get pretty beat up and end up ever decreasing the volume, even double attenuated than at the beginning. To me it can get too much.
Decreasing the bass only was never a solution because upper bass is gone also and attenuating the LFE only levels out so that every explosion and gunshot sounds too similar...
Is this a part of the problem @audio2920 suggests? Or is it mixing as such for targeting wide range of systems with different low frequency extension capabilities, so the ones that dig down low wouldn't mind after all, and others not so capable would still get a satisfying "experience"? Personally, it can be quite shocking when after a quiet dialogue suddenly you get blasted out of nowhere...
While it could be a result of this, I think this is primarily going to come from creative intent.

The bass management thing I'm banging on about would only "add bass" compared to how the mixers had it in a scenario where you're bass managing a lot of speaker to a single sub output. The more speakers and the higher the crossover frequency, the more exacerbated the effect is. So it is possible that if you're doing this AND they mixed the gunshots such that there was bass content in a lot speakers/pan positions it would have an effect. But my suspicion is what you're hearing will probably just be a "creative" decision.

I don't know anything about that particular mix example, but for a totally imaginary back story as to their reasoning; the director may say something like "We really need to make John's gunshots louder. Ya know, more impressive and powerful somehow. Like he's overpowering his enemies." The sound team have run out of headroom to make them louder (or may not want to make them any more blistering than they already are) so they make them fatter, the director says "Great!" and that's how they stay. Who knows!? :D

If you watch slightly older films people tended to do a lot with pitch to clarify the story in fast cut scenes. For example, if the main protagonists are have a battle with a bunch of "baddies", one team will have one sound pallet and the other will have a different one, with very little attempt to be literal to the gun's they've got. It's just "bang-bang-bang" = GOOD, "prap-pap-pap" = BAD.
 

Kvalsvoll

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#10
(side note: I can't put that content in the ".1" as in most default stereo downmixes the decoder mutes that off, so anyone listening via a 2.0 decode would have no bass at all.)
This is important, because now many enthusiasts move to 2-ch stereo, and even if they have subwoofers, the bass-system is managed as part of the L-R speakers so they appear as just 2 full-range speakers.
 
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#11
Sorry, maybe what I wrote was misleading. I mentioned theatrical mixing but I was only trying to convey that it's quite normal for film mixes to start their life in a big room, not that we send these out. From that point on I'm only referring to specific HE mixes. Although, frustratingly it's not as rare as one might hope that the wrong mix version gets used...
Those big room mixes are the start, and that is what is sent to me to tweak and encode for a small room. That goes for both disc and streaming environments.

I also agree with you about standards, but do feel that what I'm talking about here is not replay outside "the standard" but within it. The standard for Atmos HE replay is 2.0 up to 9.1.6 and beyond. Mixing HE in Dolby certified room in 7.1.4 with BM @ 80Hz may be a standard; it's a good starting point, and it's impossible to cover everything in the time we have to do an HE mix. But I feel like this issue, particularly in immersive mixes, could benefit from more attention than it currently gets.

The "standard" for Atmos HE is 5.1.4 or 7.1.4 speaker setups. 2.0 reproduction sources must re-encode the immersive mix to stereo and then process that mix to create an immersive effect. There is no real actual support for Atmos in stereo. In order to achieve 9.1.6, the AVR or Pre-pro must have an upmixing algorithm to support the wide mains and direct overhead speakers.

I do agree that more attention would absolutely lead to much better results....especially when talking about creating a great Atmos mix for the HE. I think movies that have been converted from 5.1 to Atmos especially for HE (The Fifth Element, Blade Runner, The Dark Crystal, etc.) show very clearly that with time and a decent budget, you can get a terrific well optimized mix.

But I guess now with so many permutations of speaker configs, my attitude to doing a mix and "letting the chips fall" (great way to describe it btw!) has softened slightly in the sense that I feel more responsibility than ever to make a single HE mix play nicely on a wide range of systems.

OMG, we tried to create a mix that would translate well on a wide range of systems (and reproduction platforms at that), and the result were very disappointing to consumers. Those mixes were so criticized and berated (Atmouse is what they called it), that we abandoned the idea pretty quickly. I never thought it was a good idea because the variables were so wide, I didn't think it was achievable.


But now, if you're unlucky with how the phase lands, someone playing that Atmos Blu-ray in a 9.1.6 BM'd room could have like 10dB more bass* than someone playing the same track in like a 5.1 non-BM'd room, even if both rooms are calibrated perfectly to the same standard. This is significant to my mind. If your DAC had a 10dB error in it you'd be pretty upset, but yet the output from an Atmos mix decode+BM strategy can have errors this large.
I would dare to say it might be good that the 9.1.6 system is getting 10db more bass than a 5.1 non-BM'd room. In order to maintain the proper spectral balance between the mains and the subwoofer, the speaker system with more speakers should have more bass than a speaker system with fewer speakers. Considering no mix direct toward the HE is done on a 5.1 non-BM'd systems, of course, there are going to be gross differences between the two systems when it comes to bass output.


I just think we should do our best to get it as far as the decoder output without major discrepancies in level or spectral content being introduced by downmixing and/or BM. It'll never be perfect, and as you rightly say, if it's a good mix to begin with, it will hopefully still stand up in the real world.
This is why Disney and Sony (and other studios as well) do very specific made for HE mixes. During our first pass, we can listen for discrepancies, and tweak and fix them before encoding. Atmos does not downmix, it adapts to the speaker setup that is configured within the AVR or processor. As far as I know, all Atmos mixes are played back in bass-managed environments, as that is a part of the cinema and home decoding process. It CAN be played back on a non-BM'd system, but the results will not be consistent.
 
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#12
on this, it came up regarding the X-Curve discussion. Are all of the major studios doing specific "home" mixes? Does that require multiple mixes and remastering (streaming mix, Blueray mix)?
I know we (Disney) are, and have been since 2000 when I started doing them. Sony, Warner, and Universal do it for specific titles. I don't use the X-curve for HE mixes, and I am not sure it really sounds the best in the theatrical environment. The X-curve was developed to counter high-frequency distortions coming from the optical tracks, and the high-frequency sections of the screen channels back in the day. I strongly believe we need to take a look at using it, and I have mentioned this in AES technical meetings. As Audio2920 correctly stated, most of the time we are doing remastering, but when taking a legacy 5.1 track and creating an Atmos mix, we are actually remixing the entire track.


"Cinema EQ and THX Re-equalization® share a common goal as they’re both designed to remove excessive high frequency information from movie soundtracks optimized for theatrical presentation."

I'm assuming that HT Receiver makers have such preset eq features is there is content, a fair amount of it, that wasn't re-mastered for HT environment?

Both of these two roll-off filters are carryovers from the Dolby Stereo and early Digital 5.1 days. I very rarely use it except on older soundtracks that are bass limited and treble-heavy.
 
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#13
Likewise, a question for both @audio2920 and @Soundmixer , why are small firearms shots in action movies so exaggerated, not so much in loudness but in frequency range? IMO, a bit surreal if it sounds more like a cannon blast rather than a simple pistol.
For example what ever John Wick has in his hands digs deep down sometimes to 35 Hz or so, and up to about 110, summed to be perceived as quick and instantaneous? This on a capable system of course results in a viewer "being shot" in the chest. By the end of the movie with thousands of gunshots and explosions, I get pretty beat up and end up ever decreasing the volume, even double attenuated than at the beginning. To me it can get too much.
Decreasing the bass only was never a solution because upper bass is gone also and attenuating the LFE only levels out so that every explosion and gunshot sounds too similar...
Is this a part of the problem @audio2920 suggests? Or is it mixing as such for targeting wide range of systems with different low frequency extension capabilities, so the ones that dig down low wouldn't mind after all, and others not so capable would still get a satisfying "experience"? Personally, it can be quite shocking when after a quiet dialogue suddenly you get blasted out of nowhere...
Honestly, making a handgun sound like a cannon is and always has been a pet peeve of mine. If a handgun sounds like a cannon, then what should an actual cannon sound like? It is done to add impact to the effect and often exaggerated the effect unnaturally. This is not mixing to a system or format issue, that is for sure.
 
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#14
I realise I'm perhaps making a bigger deal out of this than it is most of the time. But, I honestly feel this BM issue could have a lot to do with people complaining about "muddy" mixes etc. Far more so than x-curves and general EQ considerations.

I mean, my own front room system isn't even FR corrected. It's just some speakers levelled and crudely time corrected, and I have no issue with listening to that.
I think people complaining about muddy mixes have calibration or placement issues. I don't think it is the mix itself, but poor placement of the sub, sub too loud, and poorly integrated. The biggest complaint I have heard when it comes to mixes is not enough bass or too much bass. Rarely have I heard anyone complaining about a soundtrack sounding "rolled off" at the top end.
 
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Thread Starter #15
The "standard" for Atmos HE is 5.1.4 or 7.1.4 speaker setups. 2.0 reproduction sources must re-encode the immersive mix to stereo and then process that mix to create an immersive effect. There is no real actual support for Atmos in stereo. In order to achieve 9.1.6, the AVR or Pre-pro must have an upmixing algorithm to support the wide mains and direct overhead speakers.
Atmos does not downmix, it adapts to the speaker setup that is configured within the AVR or processor
You're right, I've used old-school terminology. Atmos HE is spatially encoded so it's not a downmix, but a render to a different number of speakers. However, the result is the same. To digress slightly and elaborate on why I say "the same"...

I actually feel like Atmos actually generates a discreet bed from the objects and then it does a downmix when you've got less than 7 channels at Z=0. Maybe that's not literally what happens, but the result is identical. If you pan an object to 50/50 between the "virtual" Lss/Lsr in a 5.1(.4) config, you get +3dB at that pan position, compared to hard panned to the L or Lsr position, in *exactly* the same way as when you downmix a channel based 7.1 to 5.1. I've been mixing in Atmos since 2012 so perhaps should have got my head around this part better by now :p but my suspicion is that it's so that the beds and objects behave the same.

While I see what you're saying about Atmos not having support for stereo (and it's not really Atmos unless it's got height, so 5.1.2 would be the minimum) this is totally dependant on the receiver config. Most of the time when people are streaming Atmos or it's coming off a blu-ray, the only stream is the DD+JOC which is the spatially encoded stream made from the .atmos (or ADMs or whatever). Whatever format you're listening in, it's a decode of the Atmos in a sense. Yes, it might come off the "DD" part of the stream if your receiver doesn't have an Atmos chip in it, but even in that scenario, the DD in itself (in this particular stream) is a render of your Atmos HE mix since it came from the Atmos master. My understanding of this might be flawed - I'm sure someone here will know more than me - but if you have an Atmos AVR, you can plug in basically as many or few of the speaker or pre-outs as you like, therefore you can hear the "Atmos stream" i.e. generally DD+JOC in any speaker config, including 2.0. (Whether in a non-Atmos speaker config they just use the "DD" and discard the "JOC", I don't know. I don't think the result would be different though either way?)

Anyway, sorry I've strayed off topic, but yes, I absolutely should be calling them renders not downmixes.

I would dare to say it might be good that the 9.1.6 system is getting 10db more bass than a 5.1 non-BM'd room. In order to maintain the proper spectral balance between the mains and the subwoofer, the speaker system with more speakers should have more bass than a speaker system with fewer speakers. Considering no mix direct toward the HE is done on a 5.1 non-BM'd systems, of course, there are going to be gross differences between the two systems when it comes to bass output.
Perhaps that was a bad example as non-BM is a relative oddity. However I disagree with you on the spectral balance I'm afraid. I stand by my original point; the spectral balance is not maintained by this effect. I must stress, this is only when LF is more omnipresent. If there's LF in one spatial location only, it's fine. This is because the summing of everything below the BM x-over is voltage summed and everything above that frequency is summed in-room acoustically.

This isn't a new observation from me either, Dolby are aware of it (they refer to it as "LF build-up") hence the introduction of object-based bass management in the RMU. I still [generally] mix with speaker based management for HE (and generally in 7.1.4) because I don't know of consumer systems using object bass management. If/when that changes I may revise my strategy!

This is why Disney and Sony (and other studios as well) do very specific made for HE mixes.
I'm aware and involved :)
 
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#16
I actually feel like Atmos actually generates a discreet bed from the objects and then it does a downmix when you've got less than 7 channels at Z=0. Maybe that's not literally what happens, but the result is identical.

Well....not exactly. What it does do is render to the speaker layout you have. It does not downmix at all.


If you pan an object to 50/50 between the "virtual" Lss/Lsr in a 5.1(.4) config, you get +3dB at that pan position, compared to hard panned to the L or Lsr position, in *exactly* the same way as when you downmix a channel based 7.1 to 5.1.
Addressing the first statement, Atmos treats panning to virtual positions the same way it treats panning to hard positions. If you get +6 when hard panning to an L/R position, Atmos will give you the same +6 for virtual spatial positions as well. It is not a channel-based system, so you don't get the reduction in power response to a virtual position like you do a channel-based one.


but if you have an Atmos AVR, you can plug in basically as many or few of the speaker or pre-outs as you like, therefore you can hear the "Atmos stream" i.e. generally DD+JOC in any speaker config, including 2.0.

This works down to 5.1.2, but not below that. If you are playing an Atmos track through a two-channel system, it must be re-encoded (properly folded down) to stereo before it will properly play back. In that process, the metadata in the "Atmos" stream is stripped away completely.


This isn't a new observation from me either, Dolby are aware of it (they refer to it as "LF build-up") hence the introduction of object-based bass management in the RMU. I still [generally] mix with speaker based management for HE (and generally in 7.1.4) because I don't know of consumer systems using object bass management. If/when that changes I may revise my strategy!
I agree with this point, and do exactly the same thing.
 

Andysu

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#17
So, soundmixer, audio2920 what is your imdb what movies have you mixed.
 
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Thread Starter #18
Well....not exactly. What it does do is render to the speaker layout you have. It does not downmix at all.
Yes, sorry, I get that. I think I was confusing the issue. The renderer *can* and does default to downmixing to create 5.1. It also applies this to the "5.1" of a 5.1.4. I guess for deliverables to maintain consistency with channel based variants?

You can render directly to 5.1 though, which is probably more like what would happen in a consumer unit. So mostly, you're right, I'm wrong :)

Addressing the first statement, Atmos treats panning to virtual positions the same way it treats panning to hard positions. If you get +6 when hard panning to an L/R position, Atmos will give you the same +6 for virtual spatial positions as well. It is not a channel-based system, so you don't get the reduction in power response to a virtual position like you do a channel-based one.
As above, agreed too.

This works down to 5.1.2, but not below that. If you are playing an Atmos track through a two-channel system, it must be re-encoded (properly folded down) to stereo before it will properly play back. In that process, the metadata in the "Atmos" stream is stripped away completely.
Sure, but this is just a downmix though. It's a 5.1.0 render followed by a standard Lt/Rt encoder or Lo/Ro downmixer.

We strayed off topic here (my bad) but none of this really affects the BM situation, which all exists post-render. Ha, interestingly though, the issue with BM is that it's a mono downmix of all speakers so doesn't maintain level regardless of pan :)

I have been thinking about mixes I've done in the past, and I would say that for a lot of the time the issue is negligible. I guess my "trigger" was doing one recently where that wasn't the case. When it's a problem, it's a real pain. I would say, it's always going to be more problematic on (a) mixes utilising multi-channel mic techniques, e.g. derived from ambisonics etc (b) music, particularly live music (c) stuff with lots of continuous low frequency; heavy ambiences which aren't hard panned and so on. It's clearly not going to be *such* an issue in a dialogue heavy piece set in the countryside, or even an action film where things may be massive, but largely directional. It'll still do it, but the discrepancy will be less.
 
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Thread Starter #19
So, soundmixer, audio2920 what is your imdb what movies have you mixed.
Ah you had to ask... :D Sorry, all things considered it's probably better not to give that out so easily. Not sure how "soundmixer" feels about it? (It would be hilarious if we knew each other and it's a small world so there's a definite chance, but let's not find out.)

Suffice to say my credits span low budget indies to top budget studio work - pretty much like everyone else.
 
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