# BFD Input Level?



## allredp (Feb 7, 2007)

Hey Shacksters,

Just getting my BFD 1124 set up and ran into my first snag!

I'm following the BFD guide about setting the input level by getting the in/out blinking green and then playing U-571 at loud level (-30 on my RX1200 Yamaha AVR). Then I adjust the LFE level in the AVR, right? 

The problem is that I'm all the way backed off the input level (-20 on my AVR, which has a range of -20 - 0) and the BFD is clipping heavily! The red is pretty much on continously when the depth charges are going off. 

I've got the BFD chained between my AVR (sub out to the BFD #1) and the sub (BFD #1 output to the SVS PB12+/2).

Any help would be much appreciated! I'm anxious to fire up my freshly downloaded REW and start cranking out charts and graphs like the rest of you. 

Thanks in advance,
Phil


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## brucek (Apr 11, 2006)

Your receiver may have an unusually high output level. The solution is to switch the operating range of the BFD from -10dBV to +4dBu setting. The switches are on the rear of the BFD. One for each channel.
See if you can now turn up the trim level of the LFE and use as much of the input range as possible.

brucek


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## allredp (Feb 7, 2007)

Hey Bruce!

Much obliged on that help--I'll kick the kids off the xbox and try the +4 setting tonight. With only one sub I only need to do that for channel #1 and then gain it as much as possible without clipping as I set the input level, right? 

BTW, are there problems with using the +4 setting? Since the BFD Guide is pretty pointed about using the -10 setting, I'm assuming there are some negatives... 

To be painfully clear for a low-tech such as myself, I only have one sub--so am I using just one channel on the BFD, right? It doesn't matter whether I use #1 or #2, right? If this is so, then there will only be one set of LEDs jumping, right? 

This is deep tech for a history professor!

Thanks for the help, Bruce.

Phil


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## blue_max (Feb 22, 2007)

I hope the previous suggestion helped you. I would just say that a volume level of -30 does not seem particularly loud. I live in a ground floor flat, so obviously have to be neighbourly, but my maximum level is -18. Admittedly, that is pretty loud though. My thought was whether you have some settings active on your dvd player which may boost the LFE channel. Sometimes there are settings on amps for bass boost too, which are often buried in the settings.

Graham


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## allredp (Feb 7, 2007)

Hey Graham--I hear you on that volume level, but I think that my Yamaha (nearly 6 years old now) is just goofy on the numbers. I noticed that the next year's version volume went into the + regions, whereas mine just stops at 0. 

There are a few DVDs, like Star Wars II that I can boost to -26 or so without feeling fear about blowing things, but for the most part -30 is plenty. 

I should get my RS SPL out and check the decibles to see what the SPLs are. In fact, I'll do that tonight and report back. Maybe I'm just a wanny...

Cheers, 
Phil


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## brucek (Apr 11, 2006)

> With only one sub I only need to do that for channel #1 and then gain it as much as possible without clipping as I set the input level, right?


Yep...



> BTW, are there problems with using the +4 setting?


Well, any consumer (non-PRO) piece of equipment usually doesn't have the level required to operate in the +4dBu range that a PRO system would. The +4dBu selection will realize a slightly higher noise floor, that you can establish as a problem or not by simply pushing the switch and listening at the sub to see if it is objectionable. 
Then you would like to establish if your LFE out can produce enough level to use that range. If you could get a yellow LED on once in a while that would be optimum, but if not, at least be sure it is reasonable.
The -10dBv setting allows a maximum input level of +2dBV, which is ~1.26vRMS. The +4dBu setting allows a maximum input level of +16dBu, which is ~4.9vRMS. Quite a bit higher range.



> I only have one sub--so am I using just one channel on the BFD, right?


Yep..



> If this is so, then there will only be one set of LEDs jumping, right?


Yep... 

brucek


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## allredp (Feb 7, 2007)

Sweet--I'm listening/feeling WOW when the Pods emerge! Holy Cow, the storage door next to my PB12+/2 is making horrific noises! I thought I'd done irreparable harm to the sub by ramping up the LFE level!!! Turns out I just have to get some special weather-stripping or something...

Anyway, with the BFD set to +4 and my AVR LFE set to full gain (which is 0), I am getting some yellow on the peaks, with the extreme stuff getting a touch of red. I've used WOW, XMenIII, and U-571 to get the hottest LFE. BTW, the most LFE is in WOW--where the lasers are getting some slightly sustained red on the hottest parts.

Should I back my LFE down a notch or two? Or is having some red for a second ok?

Also, Bruce, you mentioned that the noise floor will increase with the +4 BFD setting, how do I test that? I'm not noticing any noise coming from the sub, but how would I test it? Would I put on a deliberately soft passage from a DVD and try to hear something from the sub? Sorry if this is a stupid question--I just want to understand.

Graham: I've tried to use the RS SPL for getting decible readings, but I'm a newb and don't know how to use the **** thing. When I set it at 80 (C fast) it tops out at 90, when I turn the range up to 100, then I get 109 at my seating position (about 15' away from the sub). What am I doing wrong? Anything? 

Now, on to the next steps to get REW running and filters loaded...

Thanks so much for the help!
Phil


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## blue_max (Feb 22, 2007)

Here's what I have learnt...

Firstly - remember this principle. You have now got the maximum signal from the LFE port of your amp into the bfd. The only things that will affect this now are the amps volume (which you have decided is as high as it's ever likely to go) and the actual volume on the sub's amp itself. The sub could be on zero volume or max and the bfd won't care. You need to balance the subs volume to match the other speakers.

The amp should have a test tone and either manually or automatically sweep to each speaker. This has a set volume of 75db (I think this is universal to all amps). Sit at your usual position and ideally use a tripod to mount the meter vertically (microphone at the top). Set it to the 70 range, c-weighted and slow. When the sound plays, you need to adjust the speaker volume via the amps channel adjustment. The needle needs to sweep past the middle and settle at +5 to reach 75db. When it comes to the sub, you need to adjust the sub's amp volume - it is not easy to measure, but see if you can it's sweep at the middle of +5. You then have your speakers balanced.

When you use REW, it's best to use the 80 scale as it gives more headroom.

Hope that helps.
Graham


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## brucek (Apr 11, 2006)

> Turns out I just have to get some special weather-stripping or something...


Everyone with a capable sub has this problem. Picture frames on walls are bad too. They rattle like crazy until you put a small piece of something behind the bottom part of the frame where it touches the wall. My fireplace doors are also bad. 



> Should I back my LFE down a notch or two? Or is having some red for a second ok?


Your OK. Leave it.



> you mentioned that the noise floor will increase with the +4 BFD setting, how do I test that?


This setting raises the entire input/output operating level of the BFD. Internally there's no real change. So if I feed a 1volt signal into the BFD, it will be 1volt (with no filtering) at the output, irregardless of the operating level switch.
But the -10dBV setting which has an operating input/ouput range of 0volts-1.25volts, would obviously be more sensitive to a very weak signal. If you have a strong output voltage swing from your receiver that clips this input, then you need to move to the next operating range. The test is whether you can make those LED's move in this higher range. You have satisfied this requirement. 

There will be a small increase in the noise floor at the +4dBu setting, but it likely isn't noticeable. Simply turn your receivers volume down to zero. With the BFD and sub on, switch between the low and high operating range. Notice any noise floor change? If it's not objectionable, you're good. Either way, you simply have too much signal for the -10dBV range....



> I've tried to use the RS SPL for getting decible readings, but I'm a newb and don't know how to use the **** thing


You'll have to learn. Only use slow setting and C-weight.
Re-read what blue-max said below. You need to use the Radio Shack SPL meter initially (before REW) to set up your speaker levels. It's more important that they're matched at the same level, than what that level is. You do this with the receivers internal test tones. You adjust the speaker trims to match the levels of all the speakers *except for the LFE sub trim that you've already set and shouldn't now touch)*. Its level is set with the sub amplifier volume. (I run my sub hot, as do many others and prefer the sub level higher than the rest. This is up to your ears)

brucek


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## allredp (Feb 7, 2007)

You guys are good!:clap: 

So, I'll get my 6 main/center/surrounds all matched tonight--I've done it before, but with the other tweaking I've done I should be sure. I won't mess with the LFE trim, as per Bruce's instruction. :whew: 

In line with Bruce's comment about meter reading, I'm assuming that with a digital RS meter I am just getting them all to have the same number--whatever it be. E.g. if my normal listening level on the AVR is -36 and I turn on the RS SPL to 70 range, C weight and slow, as the test tone sweeps through each of the channels (sans sub), I adjust their individual trims to all equal the same number (it might be 68 or 69 if I recall in my case). That makes sense. 

Graham's comment about the "needle" refers to an analog RS meter, right?

I can't wait to continue this tonight!

One more question for now: how does one calculate spl for extreme LFE? I hear people talk about getting 115db on a certain scene, or 112db on another, etc. Does the RS meter do that for you? If you could explain, I'd love to see what kind of numbers my PB12+/2 is cranking out for comparison! :flex: 

Thanks again!
Phil


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## lovingdvd (Jan 23, 2007)

Sounds like you have a Yamaha receiver?

At any rate as may have been covered I don't think you want to use the LFE -20 to 0 adjustment for LFE. Instead just use the general SUB level output.

Also as a side note - I use the opening scene in Start Wars III for the input level test. Right after the opening theme song and just before the first space ships are on screne there is very powerful bass that starts pounding in the sub.

Another scene I use to spot check the level is King Kong HD DVD I think around chapter 31-33 (somewhere in there). There are scenes when Kong is letting how huge grunts most of which is LFE. Nice!


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## allredp (Feb 7, 2007)

Yes, I have a Yamaha RX1200 AVR--which is great, but I don't like being stuck with only a 90hz x-over for the LFE! I'm also suspect of the 80 wpc when driving all channels--my Dahlquists are rated up to 250wpc and I don't think I'm giving them enough stuff to sing like they should.

So, I guess I spaced/didn't know there was an LFE trim in the Speaker setup menu with all the other channel stuff. I just worked through the menu and found the #10 menu (if I recall correctly) that is called LFE level.:duh: 

I'll look more closely at the earlier menus to see what you mean. Maybe that's the difference with my needing to use the +4 on the BFD instead of the usual/preferred -10.

I appreciate the demo insights also--I'll check those out soon. 

Thanks for that help!

-- Phil

PS I'll also check out the noise floor as per Bruce's directions--I think I missed that in his earlier post.:reading: 

Much obliged...


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## allredp (Feb 7, 2007)

lovingdvd said:


> Sounds like you have a Yamaha receiver?
> 
> At any rate as may have been covered I don't think you want to use the LFE -20 to 0 adjustment for LFE. Instead just use the general SUB level output.


So, last night I went back through my Yamaha menus and can't find any "sub out" other than the #10 menu option (-20 - 0). Am I missing something? onder:


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## lovingdvd (Jan 23, 2007)

allredp said:


> So, last night I went back through my Yamaha menus and can't find any "sub out" other than the #10 menu option (-20 - 0). Am I missing something? onder:


Yes you are missing something. In one of the set up menus you'll find input level controls. As you cycle through them you'll see options to add or subtract gain for the left front, center, right front, each surround, and finally the sub (which is the one you want to adjust for this).

Let me know if you still cannot find it and I'll go through my Yamaha menus to let you know where it is (although my model is different its likely in the same menu org).


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## allredp (Feb 7, 2007)

I thought that's where it would be also, but when I cycled through all the other speaker's -/+ it comes to "sub" but only allows me to select between "sub", "main", or "both". There's no -/+ option there!

This is the 1200 (Yamaha is out with the 1700 now) and so it might just be too old to have the LFE trim with the other speaker sets. 

As I mentioned earlier, this model also doesn't have a variable x-over point for LFE--it is stuck at 90hz only. Which really stinks, I think, because my mains are capable down to 30hz!

I'll have to upgrade at some point, of course...:spend:


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## Wayne A. Pflughaupt (Apr 13, 2006)

lovingdvd said:


> Yes you are missing something. In one of the set up menus you'll find input level controls. As you cycle through them you'll see options to add or subtract gain for the left front, center, right front, each surround, and finally the sub.


According to pg. 24 in the on-line RX-V1200 manual, the sub isn’t included in the rotation – just the main speakers. That leaves the LFE option in the menu as the only alternative. It’s supposed to only work with Dolby Digital, which makes you wonder what's going to happen to your sub level when you switch to music or Pro-Logic for TV shows. :huh: 

Regards,
Wayne


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## lovingdvd (Jan 23, 2007)

allredp said:


> I thought that's where it would be also, but when I cycled through all the other speaker's -/+ it comes to "sub" but only allows me to select between "sub", "main", or "both". There's no -/+ option there!
> 
> This is the 1200 (Yamaha is out with the 1700 now) and so it might just be too old to have the LFE trim with the other speaker sets.
> 
> ...


You are in the wrong menu. There's a sub menu somewhere called Levels. Forget LFE trim that is not what you are looking for. If you need further help finding it let me know I'm sure it is in your menus.


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## lovingdvd (Jan 23, 2007)

allredp - here is exactly where these controls are in my menu (Yamaha HTR-6090 which is basically a clone of the RX-V1700).

MANUAL - > 1. BASIC - > B. SP LEVEL

Within SP Level you should have all individual speakers in there. If not make sure your speaker set is configured to show that you have a subwoofer in the system. Let me know if this helps.


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## allredp (Feb 7, 2007)

ok, I've found the "level" button on my Yamaha 1200 remote. Here I can adjust the trim of all the peripheral speakers--center, sr/sl, rear center, and sub. 

Turns out this is the same trim as the #10 in my "menu" options. It was at 0, and backs down to -20, just like the #10.

So, mystery solved! 

However, like Wayne pointed out, there may be a serious issue when not in Dolby mode--though I haven't found this to be the case in listening to TV source material through my HTPC.

Thanks again for all the help!


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## lovingdvd (Jan 23, 2007)

*Oops! Had +4 -10dB switch in the wrong position!*

I made an interesting discovery today by accident. When I initially set things up I was sure to push the +4/-10dB switch IN so that it was set to -10dB.

HOWEVER, I didn't realize that there are actually TWO switched - one for input and one for output.

So I just realized that this whole time I've had the INPUT set to +4 db. The output was set to -10dB as expected.

This brings up the question - does this really matter? I'm assuming the answer is a resounding YES. If not, please let me know!

So my next step is to push the switch in for -10dB, and then bring my sub woofer output level in the receiver down accordingly.

My two main questions about this are:

1) Does it even matter (already asked above) if I was to just leave it the way it is? 

2) Will it be necessary for me to fire up REW again once I change the levels and recheck for peaks and the filters (basically recheck the calibration)? If changing the levels would not really affect that, that would be good news as it is a bit of a pain to drag out the PC and set up all my equipment to use REW.

Thanks!


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## brucek (Apr 11, 2006)

> HOWEVER, I didn't realize that there are actually TWO switched - one for input and one for output.


No. One for left channel, and one for right channel.



> Does it even matter (already asked above) if I was to just leave it the way it is?


Set it to -10dBV for each channel if you have a receiver where that matches the input level that feeds the BFD.



> Will it be necessary for me to fire up REW again


No, but be sure the RED LED(s) don't come on when playing loud levels. Just the Yellow LED(s) should come on when very loud passages are played. Adjust sub LFE output trim for this..

brucek


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## lovingdvd (Jan 23, 2007)

brucek said:


> Set it to -10dBV for each channel if you have a receiver where that matches the input level that feeds the BFD.


How do I know if my receiver matches the input level that feeds the BFD?



> Adjust sub LFE output trim for this..
> 
> brucek


But isn't it more than just the LFE trim? Adjusting LFE trim would not reduce the bass that is redirected to the sub for all other channels set to SMALL, correct?

In this case rather than adjusting the LFE trim I should use the general sub woofer line level output control (just like is available for all of the 5.1 channels, no?

Lastly, is there really any difference here? For example if I have the receiver sub woofer output set to +6dB for the sub when the switch is at +4dB, does it make a difference if I set the switch to -10dB but then raise the sub output 14dB to 20dB?

Come to think of it, the sub outout is already around 7dB with the switch at +4db. If I move the switch to -10dB I will have to basically pin the output control for the sub output at 20dB (which I believe is the max) and that may not even be quite sufficient. With this i mind perhaps I should leave the switch at +4dB? Thanks!


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## PeteD (Sep 9, 2006)

lovingdvd said:


> How do I know if my receiver matches the input level that feeds the BFD?


This is part of the whole balancing act of adjusting your receiver sub out level with your sub amp level and seeing if that produces clipping at the BFD. It is also a function of the boost or cuts that you put in as filters and you need to check for clipping of the BFD input and output (if you use any significant boost) to make sure you are optimized.

In my case, I am using boost to avoid operating the BFD at +4, because the noise floor is raised to an unsatisfactory level at +4 in my opinion with my setup. This is really a case by case evaluation that you need to perform. If you have a lot of really large cuts, you may want to add some boost in places and bring the input level (to the BFD) down. Of course, this assumes that you already have your sub amp maxed out, which boosts the signal after the BFD. Leaving headroom on the table there can cause problems with BFD input clipping.

Pete


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## brucek (Apr 11, 2006)

> If I move the switch to -10dB I will have to basically pin the output control for the sub output at 20dB (which I believe is the max) and that may not even be quite sufficient


The -10dBV setting is the most sensitive position, requiring less signal from the receiver...



> Adjusting LFE trim would not reduce the bass that is redirected to the sub for all other channels set to SMALL, correct?


LFE trim means receiver subwoofer output level (or whatever your model calls it).

brucek


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## lovingdvd (Jan 23, 2007)

PeteD said:


> In my case, I am using boost to avoid operating the BFD at +4,


I was under the impression that using filters that add boost is not advised. This may actually not be the case in your situation but I just wanted to make sure you were aware of that.



> because the noise floor is raised to an unsatisfactory level at +4 in my opinion with my setup.


Can you please describe what you mean by "noise floor" exactly? Do you mean what you hear out of the sub when there is sound (input) coming down the line (noise during silent scenes)? How can I check my noise floor?



> This is really a case by case evaluation that you need to perform. If you have a lot of really large cuts, you may want to add some boost in places and bring the input level (to the BFD) down. Of course, this assumes that you already have your sub amp maxed out, which boosts the signal after the BFD. Leaving headroom on the table there can cause problems with BFD input clipping.
> 
> Pete


I had always been advised here to turn up the sub woofer input level control at the sub, and then use cuts to bring everything down.


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## lovingdvd (Jan 23, 2007)

brucek said:


> The -10dBV setting is the most sensitive position, requiring less signal from the receiver...


Thanks. So is there any effective difference in how efficient my AV receiver is and/or how the sub sounds or its noise level if I have higher output at the receiver and lower input (+4db) at the BFD, versus lower output at the receiver and higher sensitivity (-10dB) at the sub?



> LFE trim means receiver subwoofer output level (or whatever your model calls it).
> 
> brucek


Thanks for clarifying. Just a heads up that on the Yamaha receivers (and likely others) there are two different level adjustments for the sub. There is the general sub output level which controls the output level for everything related to the sub (LFE + bass sent to the sub for all speakers marked Small), and then there is also a specific LFE trim that goes from -20dB to 0 dB, specifically for adjust LFE (.1) signals only. So it could be easy for someone new to BFD/REW to misunderstand what you mean when referring to this as LFE trim.


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## PeteD (Sep 9, 2006)

lovingdvd said:


> I was under the impression that using filters that add boost is not advised. This may actually not be the case in your situation but I just wanted to make sure you were aware of that.
> 
> 
> Can you please describe what you mean by "noise floor" exactly? Do you mean what you hear out of the sub when there is sound (input) coming down the line (noise during silent scenes)? How can I check my noise floor?


Noise floor is a lack of high signal to noise ratio, characterized in my case by audible noise in the system when the sound track is silent.

As brucek always recommends, if you can optimize your systems using only cuts, then do it. However, in some cases, the in-room response may necessitate such large cuts that there is not enough signal left at the back end - output of the BFD - to match the mains when the BFD starts to clip its input. In this situation, some people have successfully used the +4 operating level to prevent BFD clipping. I was able to do this, but because I had to have my receiver output cranked up so high (again because of some large cuts) - the noise floor in my sub and _mains _was not acceptable.

Now brucek correctly recommends using all cuts (remember a boost to part of a cut does not really count as boost) to maximize signal to noise ratio and dynamic range. However, in some situations (mine) this sacrifices general noise for the whole system and my system sounds much better with some substantial boost filters and the corresponding much lower noise floor associated with operating the BFD at -10. My system (a quad IB coupled with a receiver (H/K) that has a more gentle sub crossover that results in increased higher frequency output) is certainly not typical and brucek's mantra about avoiding boost should work for the vast majority of people. However, I firmly believe that if you need to consider operating the BFD at +4, you need to evaluate the noise floor of the overall system and consider using some boost filters instead.


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## goatfarm (Mar 31, 2007)

brucek said:


> LFE trim means receiver subwoofer output level (or whatever your model calls it).
> 
> brucek


LFE trim, at least on my receiver, is NOT the same as subwoofer output level. Rather it is a ratio or relationship between the LFE channel and the other five channels in a 5.1 configuration. It starts at zero (perfect +10 dB relationship) and goes down from there. There is a completely different adjustment for subwoofer output that is not related to the LFE channel. But I may be wrong here since this is my first post on this forum

I'm Greg. I love Home Theater. Been at it for years. Got a BFD, a corner sub and two powered towers. Would love to discuss the many ways to configure this system (I think I've tried them all).

All the best.:wave:


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## lovingdvd (Jan 23, 2007)

goatfarm said:


> LFE trim, at least on my receiver, is NOT the same as subwoofer output level. Rather it is a ratio or relationship between the LFE channel and the other five channels in a 5.1 configuration. It starts at zero (perfect +10 dB relationship) and goes down from there. There is a completely different adjustment for subwoofer output that is not related to the LFE channel. But I may be wrong here since this is my first post on this forum
> 
> I'm Greg. I love Home Theater. Been at it for years. Got a BFD, a corner sub and two powered towers. Would love to discuss the many ways to configure this system (I think I've tried them all).
> 
> All the best.:wave:


Yes this is what I've posted here recently. This is critical people understand this. Using the LFE level from -20dB to 0 on the Yamaha is NOT the proper adjustment for what setting BFD input level is like, and will mess up you sound pretty good - unless I guess all your speakers are set to Large. Otherwise you should use the general sub woofer output for this.


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## goatfarm (Mar 31, 2007)

I'm not even sure why receiver makers put an LFE level adjustment on their equipment since it just confuses people. As far as I can tell from all I've read it should always be left at zero anyway. That's what gives the proper balance between the LFE channel and the other 5/6/7. Even with all speakers set to large and no sub, adjusting it would definitely have an audible effect since the LFE channel would be rolled into them.


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## brucek (Apr 11, 2006)

> I'm not even sure why receiver makers put an LFE level adjustment on their equipment since it just confuses people.


Well exactly. The THX specification imposes restrictions on the LFE channel, setting its volume to +10dB compared to other channels and limiting its bandwidth. The fact that some receivers add an adjustment for this level seems unnecessary. My Bryston SP2 processor has a THX Ultra2 spec and has no such control. In fact, no processor I've ever owned has had this questionable feature. It appears to be a new affectation from manufacturers to attract button pushing.

I didn't mean to steer anyone astray with the LFE trim reference, I was of course referring to sub out level.

brucek


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