To bass manage or not to bass manage

[minister]

hi Minister,

From your posts, it sounds like you may be confusing bass management (bass re-direct) with the LFE channel as Dolby defines it.
Bass management should be employed in small rooms with smaller monitors for all the reasons explained by Pascal. This is part of the rooms monitor system and should not be turned off ever. The room should be pinked and tuned with bass management engaged. Bass management, simply put, is an attempt to emulate a large full range speaker system with smaller transducers. The goal is, the flattest most accurate monitoring you can achieve in that space.

If you have larger, full range speakers (whatever that might mean to you) then bass management may not be required. But if you are in a small room you should use it.

Your problem quoted above, sounds more like a room dependent problem or a miscalibrated system. As Pascal pointed out, room modes may have been excited by low end coming from different point sources and causing a build up of low energy at mix position.

hey eric!
wow, why do you think that i am confusing bass redirect with the LFE channel? i thought i explained the difference. apparently, i am not making myself clear, and it could be because i am tired.

the mistake i described was made because i was not all that familiar with 5.1 ... why would you think it was a room dependent problem? i simply did not send anything to an LFE (channel) in my first mix (because i was hearing it being redirected and wasn't aware that theater would not re-direct). so nothing was in the LFE channel going into the SUB woofer when i went to the theater. had nothing to do with a room problem. it was operator ignorance, not a room issue. once i shut redirect off, it worked fine in my room and the theater.

i have larger (down to 35Hz) fronts...(genelec 1032) not quite full range...and a small 22Wx15.5Dx11H room. i have cal'd my 192, RTA'd my ROOM and Pinked Monitor path (with an RTA & SPL). it is all good, spot on. so i don't use bass re-direct unless i am doing a DVD mix, or checking for bumps. and my mixes translate fine to a dub stage and theater. my broadcast mixes also translate fine. but apparently, my writing does not. that said, are you suggesting that i should be using bass redirect?

[georgia]

fwiw I wrote an article for MIX mag on bass management and the use of LFE material. It's about 2 years ago.. I'll try to dig it up for you guys.

cheers
geo

[audiobrad]

Hey Tom,
Isn't this fun?!!! At the risk of totally pissing you off, I might suggest that your system might be miscalibrated. Before you start teeing up balls and whacking them my way, hear me out. One of our first 5.1 projects was for the Omni Theater. Our room was "spot on" also. But when we played a test mix in the theater - the low end was way off (I can't remember which way - but it was embarassing). So I consumed everything Tomlinson Holman wrote and all the pdfs on the Dolby website. To make a long story short, I somehow had managed to flatten my room, but have the sub set up wrong. Since fixing that, our mixes have translated very well in theaters (so far). Our room is small too, but if your room is free of nasty low-end resonances and your system is calibrated properly, I can't think of any good reason why you're mix would sound "big and boomy" in your room (regardless of how you directed the bass) and not sound close in the theater.

That being said, I think sending the rocket to the LFE is appropriate simply for headroom reasons. Afterall, the only reason the "boom track" even exists is to buy 10 more dB of headroom in the track. If my thinking is on here (and I'm sure someone will correct me if its not), if it weren't for headroom issues, we probably wouldn't have an LFE track. We'd all just send as much boom as we needed into the main channels and we'd have crossovers in the theater to route the lowest stuff to the sub.

It's also possible the theater you played back in was out of cal (I've seen that before).

In the end, our bass management will be staying on - whether it's for DVD or theater. You may have more options with the 1032's.

Goodnight.
Brad

[abluesky]

long day of mixing.... brain tired...

i agree with what pascal said, it is what i understand.

brad, i am not jousting you about. i did not confuse the LFE channel with the SUB as part of a monitor system. if you think i was making comments to you via a moving target, that was not my intention. yes, your monitor system crosses over at 80Hz, i think my genelec system will crossover there when engaged too. and then, yes, i was talking about the LFE channel (not the SUB monitor, or where the crossover for it vis a vis the georgia satellites, not YOU, georgia , but the band) as dolby defined it. i can see how you would think i might be confusing you with this because i left it dangling out there.... sorry for not making that absolutely clear.

you were seeming to make a point about never turning off the bass redirect even if you were sending a mix to a dub stage. i was trying to say that that is a mistake. one mistake being that once you are in an environment where there is no bass management, and you weren't careful about what and how you sent things to the LFE channel, your mix might me missing some lows. if content in a bass redirected system is merely sent to the satellites (like you sort of mix 5.0), the low end might sound perfectly fine. but if you took that to a non bass redirected system, it would not play back the same. that would be something to definitely watch out for when mixing in a bass re-directed system for something destined for the cinema. let me give you an example. one of my first mistakes was mixing a rocket launch with bass redirect on. sounded big and boomy in my room. (a small room btw.) but then i took that mix to a theater as a test. what happened to the low end? in the bass re-directed system, all frequency content that was in the channels going to the satillite was being played in the room. i didn't think to send any to the LFE as the bass redirected system was telling me, all systems go (or so i thought). but in the theater, nothing was being redirected. rather than leaving redirect on, i shut it off and bussed some filtered low end from the rocket launch sound i had to the LFE and then i was in business. and maybe you wouldn't do that, (i am saying ONE might) but i did.

i can see how a blue sky (or maybe your m&k's???) can only function with bass re-direct always engaged given how far the satellites go down...and they function great like that as a system...so what to do in that situation is a little unclear to me...what to do with the stuff between 80 & 120?...my LFE output on my 192 would go where, in this system, if i knew i was going to a stage and then a theater in SR•D with a 20-120 range LFE channel?? i guess let the blue sky (which i know is an excellent system) do it's thing, make judgments based on that and then, it ought to translate to the dub facility just fine? just trust that it is being represented properly between the sat's and the sub? (which it may be, i just ask.) is that what people are doing?

another question, again, not a hostile one, for pascal, or anyone else who understands this, completely related to the above: if there is going to be THX or other bass redirected system in a theater, and dolby defines the LFE as <120Hz, how do you deal with the content between 80-120? if the crossover of the system is 80, then i'd guess you would simply have to know that before hand and mix that way. right? or no? again, trust that the sat's and sub represent it just as well as a discreet system.

The LFE Channel in a bass-managed system is not affected by the bass-management electronics and crossover network (at least not in a properly designed bass-managed system). Our systems sum the bass-managed LF channel information (post crossover), with the discrete LFE channel, which then goes to the direct subwoofer input. For our monitoring systems we typically use an 80Hz crossover between SAT and SUB, but the LFE channel has a 120Hz LP Filter (per Dolby specs). So the LFE channel's bandwidth has nothing to do with the bass-management crossover network and therefore nothing is missing.

With regard to how a mix sounds on a bass-managed system, as compared to a non-bass-managed system: If the bass-managed system is calibrated correctly, and the speakers that you are comparing the system to are also full-range, then it should be very similar and translate well (room acoustics and other 'things' all being relatively equal). If your mix sounds bass heavy in the smaller room, that could be because of room modes & other acoustic issues (sub placement etc), and / or there could be an issue with regard to calibration. Conversely, there could also be problems with the playback system in theater you are comparing it to, such as not having good LF extension.

In general, our users have told us that they have had a great deal of successes taking a mix that was created on our bass-managed systems and then moving it to a dub-stage / movie theater.

I hope that helps...

Cheers!

[Eric L]

Not to keep beating on the dead horse, but in response to why I said that here are some of your statements that confused me...

if you employ bass re-direct and send things into the Lfe, then you won't be monitoring how it will playback in a theater.

This is not true, if the bass managed system is properly calibrated.

bass re-direct is a monitor (or controller) thing. by, sending to the LFE, i mean mixing in PT. so, yes, "in a sense", i am "bass managing" some content of my mixes by sending some sounds out to an LFE bus and setting up a hipass filter to make sure it goes into the output for the sub.

This is not what "bass management" means. It is completely independent of the LFE track. So, no, all you are doing is sending info to the LFE.

in film mixing, you turn off bass re-direct. you don't LOSE anything by doing that, as long as you can monitor the content of your mix accurately. as far as making your own decisions, if you were set up for a theatrical, you would not by using bass re-direct on a dub stage. so, it is a mistake to be listening to it in your room with bass re-direct engaged and make judgments about it as it will not play back that way.

This is confusing. If your room and monitor system requires bass management to be "full range" then you lose all the low end once you defeat bass management, due to the frequency range limitations of the other speakers. You may keep info sent discretely to the LFE, but the low end carried by the other tracks will be missing. You will not be able to monitor the content accurately without bass management on a system that requires it.

so what to do in that situation is a little unclear to me...what to do with the stuff between 80 & 120?...my LFE output on my 192 would go where, in this system, if i knew i was going to a stage and then a theater in SR•D with a 20-120 range LFE channel??

Your LFE output from your 192 would go to the LFE input of your monitoring system, which would have a +10dB boost. This would then be sent to the subwoofer. If your system is not bass managed, then it would go directly to the sub, which would still need a +10dB gain adjustment (as per Dolby's spec) But then the sub would be for the discrete LFE only. On some bass managed systems, 120 hz could still come from a satellite speaker depending on the system, but on others that would be routed to the sub. So the 80 to 120 hz content would be "managed" accordingly as per the system specs. But if it is meant to be an LFE "effect", then you would send that content to the discreet LFE track. It depends on the effect.

another question, again, not a hostile one, for pascal, or anyone else who understands this, completely related to the above: if there is going to be THX or other bass redirected system in a theater, and dolby defines the LFE as <120Hz, how do you deal with the content between 80-120? if the crossover of the system is 80, then i'd guess you would simply have to know that before hand and mix that way. right? or no? again, trust that the sat's and sub represent it just as well as a discreet system.

Again, the LFE has nothing to do with system cross overs. Theatrical speaker systems have multiple crossovers. Usually divided into three ranges...low, mid and high. Crossover points vary by manufacture, but are usually around 80 to 120hz for low to mid and 1k to 2k for mid to high. LFE is independent of these, and sent only to the subs.

the mistake i described was made because i was not all that familiar with 5.1 ... why would you think it was a room dependent problem? i simply did not send anything to an LFE (channel) in my first mix (because i was hearing it being redirected and wasn't aware that theater would not re-direct). so nothing was in the LFE channel going into the SUB woofer when i went to the theater. had nothing to do with a room problem. it was operator ignorance, not a room issue. once i shut redirect off, it worked fine in my room and the theater.

This is what confuses me most. I don't understand how defeating bass management in your room, fixed the lack of low end in the theatre. If the speakers require bass management (ie they are not full range), then defeating the BM will not allow you to monitor frequencies below the range of the satellites, thus causing more problems. If there is nothing in the LFE, then any low end you hear in your room is coming from the other speakers. If you go to the theatre (with full range speakers) and that low end is missing, and you still have nothing in the LFE, then where was that low end info coming from in your room?

This is why I thought it may be a product of the room. If you hear the low end on your non full range speakers, it should be also be there on the theatres full range speakers, regardless of what is or isn't on the LFE track.

i have larger (down to 35Hz) fronts...(genelec 1032) not quite full range...and a small 22Wx15.5Dx11H room. i have cal'd my 192, RTA'd my ROOM and Pinked Monitor path (with an RTA & SPL). it is all good, spot on. so i don't use bass re-direct unless i am doing a DVD mix, or checking for bumps. and my mixes translate fine to a dub stage and theater

My intent was not to question your room, nor your mixing abilities. I was just confused by your comments, and in the name of clarity, I thought I would speak up. If nothing else, to make sure I understand this correctly. If you do not use bass management, and your genies go full range (as you have described) then your mixes will translate fine in theatres. However, I think it is not the right advice to suggest that the original poster should defeat his bass management. I believe that this will cause more problems for him if his speakers need it.

[minister]

morning fellas.

ok. i get it now. i can see how you would be confused by some of my posts. i wasn't as confused as you thought, but i see where i was wrong. i was wrong to suggest that bass re-direct be defeated in a system that needs it, even though i don't use it when it is not needed -- and i wasn't clear about that advice. i am clear now about how a system such as blue sky would handle the LFE channel. (i am sure that the mixes translate, otherwise, people wouldn't use them. i certainly wasn't criticizing this system or any other system like it.) hopefully my muddling helped someone be clear about a few things here.

a question about that. in a bass-redirected system such as a blue sky, where is the information from the LFE channel that is above 80Hz? in the the SUB or the satellites? i would think it would have to be distributed. did i just answer my own question? that was what my question was in one of my posts that i am still curious about.

the reason that i had a problem with that mix, i found out, was that their system did not have full range fronts, nor, were their crossovers setup right. the mains had a rolloff starting at 50Hz, so all that stuff at 40 was disappearing. when i remixed putting information in the LFE channel (where it wasn't before) then the mix sounded fine in their room. thing was, both versions, bass re-directed (no LFE info) and bass not re-directed (LFE info) sounded fine to me in my room.

brad, thanks for the suggestion. yeah, early on, it is confusing on how to set things up when you haven't done it before and you are getting info out of books and articles rather than having a trained technician show you how to set it up. i did it once. and then i did again. cause it wasn't right. when i made some changes in the winter, i checked it again. with bass re-direct on and with it off. it is fine. this was the only time i had this problem, and as i said, i just found out it was their room. i have heard my mixes in several different venues and mix rooms, and they translate as i expect.

[1150Post]

fwiw I wrote an article for MIX mag on bass management and the use of LFE material. It's about 2 years ago.. I'll try to dig it up for you guys.

cheers
geo

Would love to read it...

Brad McIlvaine

[abluesky]

morning fellas.

ok. i get it now. i can see how you would be confused by some of my posts. i wasn't as confused as you thought, but i see where i was wrong. i was wrong to suggest that bass re-direct be defeated in a system that needs it, even though i don't use it when it is not needed -- and i wasn't clear about that advice. i am clear now about how a system such as blue sky would handle the LFE channel. (i am sure that the mixes translate, otherwise, people wouldn't use them. i certainly wasn't criticizing this system or any other system like it.) hopefully my muddling helped someone be clear about a few things here.

a question about that. in a bass-redirected system such as a blue sky, where is the information from the LFE channel that is above 80Hz? in the the SUB or the satellites? i would think it would have to be in the sub, otherwise, it would get re-directed to the sub. did i just answer my own question? that was what my question was in one of my posts that i am still curious about.

The LFE channel is not affected by the bass-management electronics / system crossover and the LFE channel is reproduced, in its entirety, by the subwoofer(s).

Here is a link to a signal flow diagram that shows how our BMC works.
www.audiodesignlabs.com/signal1.jpg

Cheers!

[audiobrad]

It's a whole bass management/LFE seminar in one thread! I'm going to print this thing out for future reference. (Hope I have enough paper).

Brad
over and out

[Rick Sanchez]

The block diagram helped me understand the Blue Sky system. Thanks for that.

Now, in most systems (bass managed or not), where is the low pass filter (for the LFE channel) in the chain. Does it vary from system to system or is the filtering done on the actual program material before it leaves the dubbing stage? From the looks of the blue sky diagram, you can choose whether or not you want to use the 24db / oct 120Hz Low Pass filter. Is this filter built in to the system?