Bass management redirection and LFE +10db?¿?¿

watermanpc

Active Member
Hi all, I would like to have some help understanding this issue given I feel more confused the more I read about it.

Simply put, when I adjust subwoofer LEVEL in the Avr and in the subwoofer's amp to read, let's say, 75db in the listening position, exactly, what am I calibrating?, I mean, is that LFE ONLY?. What about the redirected bass from other speakers?, how do the +10db boost of the LFE affects redirected bass?.

I suspect, that if I perform the above mentioned 75db level calibration at the listening position for the sub, that will be the LFE channel level ONLY, which already has the +10db boost, but all the redirected bass from other speakers (when set to small at any given frequency) will therefor, be listened at 65db (suposed both, the LFE and the redirected bass were mean to be at the same relative level) in the listening position. Is that correct?

I wonder this, because when I listen to a content with not much LFE ("U2 go home DTS" for instance), with the fronts set to LARGE AND subwoofer set to YES, I can hear much more bass than when I set all speakers to small and let the sub do the LFE+redirected bass. However, if I turn subwoofer level up by EXACTLY +10db in this last configuration, I then listen to pretty much the same level of bass that I did with the mains set to LARGE (ignore room modes and different frequency response of each speaker and sub). This leads me to believe that redirected bass from speakers is actually -10db lower than the specific LFE (.1) conten and thus, if I use bass management I will lose the redirected bass by 10db.

I own an onkyo 3008, and it has a setting for LFE for multi channel listening, DD, DTS, DTS HD, etc. called "LFE Level" that can be adjusted to: -infinite, -20db, -10db or 0db.

I wonder if, in order to let the LFE and redirected bass to play at the same level, it could be a good idea to set LFE Level to -10db and then increase subwoofer level from the actual -7.5db to +2.5db (so +10db) to compensate for the decreased LFE level but at the same time to increase the levels of the managed bass from other speakers.

I haven't done this test already, just because I'm not sure this is the way this all truly works so I would like to have some feedback from you guys before messing with the system, as the idea is to UNDERSTAND how this 10db boost of the LFE works and how it handles the managed bass.

thanks!
 

Mr Wolf

Well-known Member
Simply put, when I adjust subwoofer LEVEL in the Avr and in the subwoofer's amp to read, let's say, 75db in the listening position, exactly, what am I calibrating?, I mean, is that LFE ONLY?. What about the redirected bass from other speakers?, how do the +10db boost of the LFE affects redirected bass?.

The +10dB boost to the LFE channel is independent of the redirected bass for other speakers.

The diagram below should help your understanding. It depicts a processor's signal flow for a 5.1 system when all speakers are set to SMALL and a 60Hz bass management crossover setting is applied.

1650697826923.png


Ultimately the processor treats the subwoofer as a SINGLE speaker channel reproducing the sum of the LFE channel and redirected bass from the other speaker channels.

The calibration trim level applied to the subwoofer channel adds/subtracts voltage gain to/from the encoded signal level purely to adjust for the in-room voltage to SPL sensitivity of the subwoofer, just like it does for all the other speakers. It is therefore applied AFTER the redirected bass has been summed with the LFE channel signal.

Some AVRs/processors (inc. my own Yamaha AVR) also have an adjustable LFE output setting which can be set between 0dB (default) and -10dB. This can be used to attenuate the +10dB boost applied to the LFE channel in situations where the system lacks sufficient dynamic headroom in the subwoofer to cope with maximum +30dB dynamic peaks. In effect, the +10dB LFE boost level is adjustable down to 0dB.

Hopefully this answers your questions.
 
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watermanpc

Active Member
thanks for the reply!

I have been making some tests and as I suspected, all this works as you suggested and as I though in my previous post.

If I set my main speakers (jamo c605, great bass reproduction) to large, and frequency response aside, as I have quite a flat response from mains and sub, I have TONS of bass coming from the mains, bass that I guess is designed to be reproduced relative to that 75db at reference, as I calibrated the mains. However, if I then set the mains to small (80hz crossover, for instance, doesn't really matter), then I LOST most of these main speakers bass, because, as stated here, these redirected bass is lowered -10db with respect to the LFE bass which seems to be the one sounding in the LEVELS calibration in the AVR when adjusting the subwoofer level to 75db.

I find this totally CRAZY!!!:eek:

So, basically, when we set our speakers to small, we are effectively losing 10db of bass content coming from the speakers, which is SUPPOSED to be 10db up when using big, capable speakers set in large!!!!

This is definitely an issue, and I can't believe nothing seems to be disscussed about this.

As an example, here is a situation where this issue is breaking how the sound of a movie was designed to sound:

War of the worlds, pod emerge scene. There is a shot where the pod is filmed far while slowly standing up. At this point 2 bass sweeps take place, natively FROM THE CENTER CHANNEL!!!

Well, If you set your center channel to small, YOU WILL LOSE these sweeps!!, as they will be low by 10db from your sobwoofer. However, if you have a capable center channel, and set is as large, you will clearly hear and maybe feel these 2 sweeps, as they will be sounding at the intended level.

The workaround for this, would be setting LFE level to -10db, then adjust your Subwoofer level to +10db from whatever you previously had set. After testing with this configuration, in that scene (and consistently accross the board), the 2 sweeps from the alien pod sounded amazing from my Monolith, while the LFE effects stayed at the same level as always. I definitely could feel and listen to sooooo many more bass effects that were missing from the center and surround channels now!!

What truly puzzles me is, in 100% of the manuals, and general matter literature, it is said that we are supposed to run the system at LFE=0db and redirect speakers bass to subwoofer channel setting them to small, but this way, the problems aforementioned will take place and the content will N O T sound as intended...how is this possible?¿?¿?😳
 
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Mr Wolf

Well-known Member
This is definitely an issue, and I can't believe nothing seems to be disscussed about this.
That's simple. The reason is because there is not an issue and that you are mistaken.

The LFE track gets a 10dB boost because its content was deliberately reduced by 10dB at the mixing stage for dynamic range encoding purposes. So no redirected bass is being cut by 10dB and you don't lose anything at all by setting speakers to SMALL provided the subwoofer(s):

1) have no Low Pass Filter (LPF) cutting its signal feed down - subs should be set to "LFE mode" or, if they don't have one, their highest LPF setting which should be at least 120Hz

2) have sufficient extension/SPL output capability to reproduce the bass signals being sent to them without compression

3) have a sufficiently flat in-room response (no nulls which can eliminate some content)

4) are calibrated to a output level that matches the rest of the system.

You might find this old article from Anthony Grimani (who coined the phrase "bass management') useful. Extract below:

"The ratio of the LFE level relative to the level of the bass from main channels should NOT be adjusted in the AV controller. The ratio should be such that LFE signals are 10dB louder than signals of equivalent level in any other channel. A few early DTS music releases contained LFE channels that were 10dB louder than the industry standard. For this reason, some controllers include a DTS music mode that reduces the LFE channel by 10dB. There is no other logical reason to adjust the level of the LFE channel separately from the main channel bass. Doing so irreparably alters the mix intended by the sound engineer."

 
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watermanpc

Active Member
Well, to be honest, I still think there is something wrong with all this, otherwise, I find hard to explain this:

1- Five well capable big speakers (lets suppose 10hz dead flat in room response), all set in large plus a perfect subwoofer. Perfect amplification. You listen to a movie's sound. You get "75db of bass" from the 5 speakers when reproducing the non LFE content the mixing engineers decided to natively send to these channels + "75db of LFE bass" coming from the sub. All sounds great!

2- Five speakers set to small. Again, perfect subwoofer, perfect performance from it. You listen to a movie's sound. You get "65db of redirected bass"+ "75db of LFE bass" coming from the perfect subwoofer and thus, you are losing 10db of the redirected bass. This is NOT sounding as intended per "1".

This is a FACT, I empirically tested it.

"1" or "2" must be the "correct" way, but not both as 1 =/= 2

I suspect "1" is the correct way, as avoids the bass management workaround and so, is closer to the true sound design. With small speakers, the only way to achieve "1" is by lowering LFE by -10db and rising overall subwoofer level by +10db.
 
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Conrad

Moderator
The mistake you're making is that you're sending the same source level input to the L channel as large, and then to the LFE channel and expecting the same output. This isn't how content is recorded.

As @Mr Wolf explained, content is recorded 10dB down in the LFE channel and is then boosted at the processing stage. It's a common misunderstanding and something I've often thought we need a thread on. The LFE channel isn't 10dB louder than the other channels, it just has the capability to have 10dB greater peaks (115dB instead of 105dB). In effect it's 10dB more sensitive.

If someone (a sound engineer/mixer) wants to get a 100dB peak in the LFE channel and a corresponding 100dB peak in the C channel, then they know to send 90dB to the LFE and 100dB to C. The outcome is the same. If you're measuring using REW then you need to drop the dbfs value by 10dB for the LFE and you'll get a matching output.

Side note: you also need to be careful with the frequency range that you use to measure subs, as well as microphone sensitivity. A lot of SPL meters, and especially phone mics, aren't designed to record or be accurate below 100Hz. If you use a 500Hz test tone then your levels will be off because the LPF in the sub.

The diagram that Mr Wolf shared in his first response is pre the amplification stage. Usually the LFE would be sent to the sub amp and the other five channels would be sent to their respective amplification channel. If you didn't have bass management on then all channels would still be sent to their dedicated amplification channels and the LFE channel would, I think, be routed to the L/R channels as well. Still after boosting by 10dB.
 

watermanpc

Active Member
"The mistake you're making is that you're sending the same source level input to the L channel as large, and then to the LFE channel and expecting the same output. This isn't how content is recorded."

Sorry, but that's not what I'm saying nor expecting at all. You are mixing up LFE with redirected bass according to your statement. The key here is REDIRECTED BASS, not LFE. What I DO expect is the same level of bass coming from the sub when reproducing the L channel bass redirected content than the level I get when reproducing that content from the L channel natively (supposing perfect response and capability). Otherwise the reproduction will not be as intended.

LFE is in the disscussion just because is the reference level at which redirected bass seems to be lowered 10db AND the "content" the Avr's seem to use to calibrate the subwoofer's channel level when using the pink noise. Just forget about LFE for a moment.

"The LFE channel isn't 10dB louder than the other channels, it just has the capability to have 10dB greater peaks (115dB instead of 105dB). In effect it's 10dB more sensitive."

Yes, I know that. It has nothing to do with the fact that redirected bass is effectively 10db lower than LFE. I'm not talking about "peak capability" or "room/dynamic range", the key here is the relative difference between the calibrated subwoofer level (seems to be LFE) and the redirected bass from other channels, creating a disbalance between redirected and not redirected bass reproduction in room, so I can't see how is it relevant where in the chain/stage this takes place.

"If someone (a sound engineer/mixer) wants to get a 100dB peak in the LFE channel and a corresponding 100dB peak in the C channel, then they know to send 90dB to the LFE and 100dB to C."

That has nothing to do with what we are talking here. Again, you are refering to LFE while the point here is redirected bass. The fact is that, following your example, if a sound engineer wants 100db bass peak in the C channel, and I have a perfect C channel speaker in LARGE, I will get these 100db of bass out of it BUT, if I then configure the system to redirect that C channel bass to my subwoofer (for whatever reason, not capable C speaker for instance), and of course supposing I calibrated my subwoofer channel to the same 75db level as the rest of my speakers (as per the general literature about all this) then, that C channel bass the sound engineer wanted to be listened at 100db from the C channel will be reproduced at 90db from the subwoofer and NOT at 100db!.

Simple as that.

Again, this is empirical!, and I can reproduce this systematically.

Sorry if I'm not getting it, but I have the feeling that we are talking about different things, I mean, I understand what you both are saying, but I actually tested this and when I calibrate the system to 75db, in the case of the subwoofer speaker, it seems like the Avr's, in general, use the LFE level to make that calibration (not the redirected bass levels nor a mix of both), which turns out to obviously cut then the redirected bass from other speakers by 10db so I don't know how the extra room for the LFE content or the stage at which that "boost" is performed is of any relevence here.
 
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Conrad

Moderator
Ok, that's all fair, apologies if I misunderstood you.

Are you saying that, playing a 75dB 50Hz test tone through L with the speakers set to large measures 75dB, and that playing a 75dB 50Hz test tone through L with the speakers set to small measures 65dB in your room?
 

Conrad

Moderator
Oh, actually, have you calibrated your mains and your subs to the same level using L and LFE?

If so, that's the problem. The sub should be calibrated to 10dB louder than the main if you're using LFE to calibrate it.
 

watermanpc

Active Member
Ok, that's all fair, apologies if I misunderstood you.

Are you saying that, playing a 75dB 50Hz test tone through L with the speakers set to large measures 75dB, and that playing a 75dB 50Hz test tone through L with the speakers set to small measures 65dB in your room?

That's it!. LPF set to 120Hz by the way.

But that's how it MUST be according to the diagrams, that's why I'm truly amazed about this being such a poorly disscussed thing.
 

Conrad

Moderator
That's it!. LPF set to 120Hz by the way.

But that's how it MUST be according to the diagrams, that's why I'm truly amazed about this being such a poorly disscussed thing.
Then it's a levels issue, simple as that. Not sure if you saw this as I double posted:


Oh, actually, have you calibrated your mains and your subs to the same level using L and LFE?

If so, that's the problem. The sub should be calibrated to 10dB louder than the main if you're using LFE to calibrate it.
 

watermanpc

Active Member
Then it's a levels issue, simple as that. Not sure if you saw this as I double posted:


Oh, actually, have you calibrated your mains and your subs to the same level using L and LFE?

If so, that's the problem. The sub should be calibrated to 10dB louder than the main if you're using LFE to calibrate it.

That's interesting and the reason I asked in previous post about exactly what the pink noise in my onkyo 3008 was in terms of "LFE only", "redirected bass only", or "a mix of both"?, I don't know. My old Denon 2105 made the same thing so I guess pretty much all Avrs are using the same for calibration, whatever it is.

Apparently, and given that I lost exactly 10db when redirecting bass from other speakers, I would say it is the LFE only what is being calibrated when using the pink noise in the levels menu.

About calibrating 10db louder for the sub...well, if I do that, then the LFE effects will be CRAAAAZY strong. Granted, redirected bass will be at the same level as when not redirecting but as I said, LFE would be way overdone and clearly out of what was intended. To give you an idea, calibrated at 75db, my dsp1124p is already slightly reaching the clipping area in extreme bass scenes and my bk monolith is producing extremely strong deep bass in all movies so going +10db would push the sub beyond its limits 100% and would make the content sound extremely bass heavy.

So the only solution I can think of is doing the -10db LFE trick (thankfully the 3008 has that option) and then increasing the Subwoofer level +10db(and so incresing the redirected bass ONLY while keeping the LFE at the same level). This way, the LFE will still have that +10db extra dynamic range, while the redirected bass will still sound as loud as if not redirected and properly reproduced by good big speakers.

However, what puzzles me is the fact that this doesn't seem like a "common" topic and as far as I can tell, we are supposed to simply calibrate the sub channel at 75db too, same as the rest of speakers, wich will cause this issue for sure.


This article is old but still worth reading:-


Thanks, I remember reading it many years ago...will take another look and see what I could be missing although I don't think so as the reason I read it was actually this very same topic and after reading it I still wasn't unclear about this issue so....
 

Conrad

Moderator
And this is where the LFE track being recorded 10dB quieter comes back in to play.

About calibrating 10db louder for the sub...well, if I do that, then the LFE effects will be CRAAAAZY strong.
No, it won't. It has the capability to be, but that's not how content is mastered.

Granted, redirected bass will be at the same level as when not redirecting but as I said, LFE would be way overdone and clearly out of what was intended.
Again, no. it's recorded 10dB lower so that when the boost is applied it's back aligned with the bass in the other channels. But if someone wants a peak if 10dB above the main channels they it's available.

To give you an idea, calibrated at 75db, my dsp1124p is already slightly reaching the clipping area in extreme bass scenes and my bk monolith is producing extremely strong deep bass in all movies so going +10db would push the sub beyond its limits 100% and would make the content sound extremely bass heavy.

Can you sweep sub only on the L channel, LFE, and L only (full range) in REW? It does sound like there's an issue, but I suspect it's a levels issue.

So the only solution I can think of is doing the -10db LFE trick (thankfully the 3008 has that option) and then increasing the Subwoofer level +10db(and so incresing the redirected bass ONLY while keeping the LFE at the same level). This way, the LFE will still have that +10db extra dynamic range, while the redirected bass will still sound as loud as if not redirected and properly reproduced by good big speakers.
You could try that. It's possible you're getting a double boost somehow. I'd take the measurements first though.

However, what puzzles me is the fact that this doesn't seem like a "common" topic and as far as I can tell, we are supposed to simply calibrate the sub channel at 75db too, same as the rest of speakers, wich will cause this issue for sure.

Doesn't that suggest an issue with your chain, rather than some massive error in the way that redirected bass and LFE is managed in AVRs that nobody else has spotted :)
 

KMO

Active Member
some massive error in the way that redirected bass and LFE is managed in AVRs that nobody else has spotted :)
I certainly have seen individual bugs in AVRs, but they tend to be in niche cases.

For example, Denon AVRs that when receiving DSD over HDMI that seem decide to lower their normal LFE by 10dB automatically (to allow for SACD not having boosted .1 channel), but screw up and lower the redirected bass too.

But for the more common use cases - like playing Blu-rays - all this stuff works basically fine. There are some issues with arithmetic summing not quite working out the same as acoustic summing, but they're relatively small.

So the only solution I can think of is doing the -10db LFE trick (thankfully the 3008 has that option) and then increasing the Subwoofer level +10db(and so incresing the redirected bass ONLY while keeping the LFE at the same level).
No, that will just cock up the relative level of LFE and main channels.

Assuming you are getting a digital bitstream input to the AVR, there's no possibility of some other device having cocked up the data, so unless there's a mastering error on a particular disc (which can happen), the LFE level should normally be set to the default 0dB level, corresponding to how it was mixed.

From all your descriptions, it seems your subwoofer was too low - in effect, it should be "+10dB", yes. The bass redirection will lower main bass content by 10dB as it adds it into the "LFE" signal, knowing that the subwoofer is calibrated louder.

Before redirection: -30dBFS bass signal in L, corresponding to 75dB SPL volume
After redirection: -40dBFS bass signal in SW, corresponding to 75dB SPL volume

(The main channels are calibrated so 0dBFS = 105dB, and the sub is calibrated so 0dBFS = 115dB).

Apparently, and given that I lost exactly 10db when redirecting bass from other speakers, I would say it is the LFE only what is being calibrated when using the pink noise in the levels menu.
No, that makes no sense, does it? You're adjusting the subwoofer trim - the volume level of the subwoofer, which will be LFE and optionally redirected bass.

I'm still not actually clear how you're calibrating this - are you using built-in AVR test tones and an SPL meter? REW or similar?

You keep talking about "calibrating to 75dB", but calibrating WHAT to 75dB? Whether getting 75dB on an SPL meter is correct depends on whether the test tone playing is supposed to be 75dB. I suspect you're getting the test tone for the subwoofer wrong - the test tone is too hot, so you end up not turning up the subwoofer enough.

If you're doing sweeps in REW, using HDMI, so you can generate sweeps on any channel including LFE, then your sweeps need to be set to 10dB lower for LFE to get the same output. Running a sweep on L at -20dBFS should produce the same bass as running a sweep on LFE at -30dBFS.

I generally recommend doing all REW calibration just using main channel output, and just doing one extra check that the LFE matches, which it will if the LFE level is set correctly and working correctly in the AVR.

To give you an idea, calibrated at 75db, my dsp1124p is already slightly reaching the clipping area in extreme bass scenes and my bk monolith is producing extremely strong deep bass in all movies so going +10db would push the sub beyond its limits 100% and would make the content sound extremely bass heavy.

How loud are you trying to play here? I can believe that your single sub couldn't achieve full reference level - but if you're trying to run at up to -10dB of reference you should be fine - the sub should be capable of the 105dB theoretical maximum (at -10dB from reference) correctly-calibrated LFE would give you.
 

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