Understanding LFE, crossover frequency, and bass management - Page 2 - AVS Forum
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post #31 of 49 Old 07-22-2013, 01:56 PM
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No, this is not correct. Almost every AVR routes the LFE channel to the main channels when specifically configured as having NO SUB connected.

If this is not desired, an AVR can be tricked into dropping the LFE channel by leaving it configured as having a subwoofer connected and simply not connecting one.


I don't think an AVR routes LFE to mains if they are set to large and subwoofer is set to none. It simply does not playback LFE if subwoofer is set to none in the settings.
LFE is a low line level signal; whereas all the speakers use high level inputs. Do you have any source to back up your comments?

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post #32 of 49 Old 07-22-2013, 01:59 PM
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Quote:
Originally Posted by braveheart123 View Post

I don't think an AVR routes LFE to mains if they are set to large and subwoofer is set to none.
Sure it does.

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Originally Posted by braveheart123 View Post

Do you have any source to back up your comments?
Yeah. Me. wink.gif

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post #33 of 49 Old 07-22-2013, 03:39 PM
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Originally Posted by braveheart123 View Post

I don't think an AVR routes LFE to mains if they are set to large and subwoofer is set to none. It simply does not playback LFE if subwoofer is set to none in the settings.
LFE is a low line level signal; whereas all the speakers use high level inputs. Do you have any source to back up your comments?

I believe you are wrong too. Lets say you have large full range fronts like klipsch rf-7s but no sub yet, say like a 5.0 system for HT. So based on your theory the LFE is just lost completely. I don't believe so, I believe its routed to your fronts set to large, now whether they can fully reproduce the signal depends on your speakers. But there are some true full range floorstanding speakers such as the rf-7s which extend to 30 hz.
And signal processing is done in the AVR, before amplification. Such as LFE assignment, HP and LP filtering, and crossover frequencies.....so that high level speaker output theory is bunk.
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post #34 of 49 Old 07-23-2013, 12:42 AM
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LFE does not end at 30Hz and bass radiators of RF-7s will struggle badly reproducing Pulse lab scene or FOTP crash scene at reference volume, but you and sivadselim are very right; I was wrong and stand corrected.

Here is the source; the flow chart explains it all.

http://audaud.com/2004/04/component-reviews-part-4-of-4-2/

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post #35 of 49 Old 07-23-2013, 05:38 AM
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Hey that's cool, we're all learning here. It's productive discussion, not arguing.
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post #36 of 49 Old 07-23-2013, 06:09 AM
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post #37 of 49 Old 07-23-2013, 06:06 PM
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Quote:
Originally Posted by braveheart123 View Post

Here is the source; the flow chart explains it all.

http://audaud.com/2004/04/component-reviews-part-4-of-4-2/

Well, honestly, Lexicon's bass management scheme is more elaborate and flexible than the bass management that is available in most conventional AVRs. They can usually do what most conventional AVRs can do and then some more. I wouldn't be surprised if they include the ability to actually discard the LFE channel completely when configured as having NO SUB connected. They also might allow you to redirect the LFE to other LARGE speakers in addition to just the front R/L LARGE speakers. As well as the ability to reroute the bass from SMALL channels to not only the subwoofer but also to the R/L (and even center) LARGE speaker channels. Etc..

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post #38 of 49 Old 08-13-2014, 11:02 AM
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Thanks for this thread and it's answers, I now have a better a understanding on how lfe works in regards to the crossover

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post #39 of 49 Old 09-18-2014, 09:06 AM
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Originally Posted by PeterAlt View Post


Another question.... Why would studios mix LFE into any of the full range channels (in addition to the LFE channel)? Is this duplicate information for backward compatibility with the 5.0 DPL systems? Or is this not duplicate information and intented to create effects by manipulating the positioning of multiple low frequency effects at a given time?
I am a film re-recording mixer and can answer your questions.

For Theatrical releases, Dolby digital, 5.1, 7.1, SDDS, etc

Main LCR. -20db fs /0db VU = 85db spl
Surrounds -20db fs /0db VU = 82db spl
LFE -20db fs / 0db VU =90db spl.

We do not mix Low Frequency Effects in to the mains. It is either a direct buss to channel 6 or an aux send to a sub-harmonic synthesizer bussed to channel 6. In some cases an additional sub synth is used on a second send bussed to the mains as an additional effect. However, this is not standard. Generally the .1 channel is not used to extend the frequency response of the mains but as an effect, although many music mixes use it quite liberally. The mains on a mix stage are full range and not bass managed. Channel 6/ LFE has already been low pass filtered at 120hz / 24db per octave.

Other formats.

IMAX. 5.0 no sub. All channels 85db spl. All channels bass managed.

Dolby ATMOS. All channels other than sub 85db spl. Surround objects are bass managed to surround subs. Scalable speaker array. 128 channels. ( too much to explain here )


It has become standard policy to do home theater mixes from the theatrical Stems ( Dx, Mx, Fx, Bg, Foley ). Essentially monitoring at 80db in small Nearfield speakers ( Genelec, Dyn audio ). Mains and surrounds calibrated equally to 80db. This is generally a mastering job for dialog clarity and to retain the impact and original intent of the mix in the home environment.

I have surely left a bit out but hopefully this helps.
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post #40 of 49 Old 09-18-2014, 03:25 PM
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Quote:
Originally Posted by sivadselim View Post
Quote:Originally Posted by braveheart123

LFE is never routed to the mains even if the sub is not hooked up; one rather loses all the LFE effects if a subwoofer is not in business.


No, this is not correct. Almost every AVR routes the LFE channel to the main channels when specifically configured as having NO SUB connected.

If this is not desired, an AVR can be "tricked" into dropping the LFE channel by leaving it configured as having a subwoofer connected but simply not connecting one.
My Marantz SR8500 does not reroute the LFE to the main channel. I only found this out while playing Starwars with a sub I borrowed, I heard bass in new places. I ran some tests and I soon found out theLFE channel is lost with out a sub for me.
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post #41 of 49 Old 09-19-2014, 01:24 PM
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Originally Posted by Blacklightning View Post
My Marantz SR8500 does not reroute the LFE to the main channel. I only found this out while playing Starwars with a sub I borrowed, I heard bass in new places. I ran some tests and I soon found out theLFE channel is lost with out a sub for me.
Yeah? How did you confirm this?

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post #42 of 49 Old 09-19-2014, 01:47 PM
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Originally Posted by Blacklightning View Post
My Marantz SR8500 does not reroute the LFE to the main channel. I only found this out while playing Starwars with a sub I borrowed, I heard bass in new places. I ran some tests and I soon found out theLFE channel is lost with out a sub for me.
The LFE was sent to your speakers..they were just incapable of reproducing content that low.
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post #43 of 49 Old 09-19-2014, 02:28 PM
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Originally Posted by sivadselim View Post
Yeah? How did you confirm this?
I hooked up one of my amps to the LFE channel and fed the signal to my main speaker.

In starwars all of the Star destroyer rumble in space are ONLY in the main speaker, the LFE is dead silent at this point. In the very first explosion in A new hope the LFE gets an extra lower but not super low 40-60hz information that is not in the main channel. The main channel sounds the same if I turn the sub off and play with and without the LFE channel. Now if I hook up one tower to the LFE channel and the other to the Right channel the two speakers play different things in the explostions and this does not get summed if I setup my system to no sub. And the difference is not that the LFE plays louder (which it does for most) it was playing completing different information.

I spent hours double and triple checking. I was a little pissed as I spent many years just running full range with no sub.

I would of never noticed but I have watched starwars over 100 times and as I watched with a sub for the first time I was noticing sounds (new notes) Low and high at different points in the movies that were not there before. Star Wars (blyray) is mixed differently then a lot of other movies. Parts with heavy bass are NOT in the LFE like large ship fly bys or blast doors closing. The LFE is only used for explotions and the full band is used (up to 120hz). The rear channel is never used for music or rain or enviroment. The rear channel is only used for lasers, falling objects,and small sounds (1% of the movie). The side channels are used 90% of the time as music is a big part of the movie.

Disclaimer: this is only for Starwars 4,5,and 6 I did not check 1,2,3.

Quote:
Originally Posted by Alan P View Post
The LFE was sent to your speakers..they were just incapable of reproducing content that low.
First, my speaker could play lower than the Sub that I had at the time but it was not the really low bass that was missing. The sub had a filter around 30hz and the driver did not move below 16hz. It was just a cheap sub.

Last edited by Blacklightning; 09-19-2014 at 02:42 PM.
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post #44 of 49 Old 09-19-2014, 02:49 PM
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And how does this...

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Originally Posted by Blacklightning View Post
I hooked up one of my amps to the LFE channel and fed the signal to my main speaker.

In starwars all of the Star destroyer rumble in space are ONLY in the main speaker, the LFE is dead silent at this point. In the very first explosion in A new hope the LFE gets an extra lower but not super low 40-60hz information that is not in the main channel. The main channel sounds the same if I turn the sub off and play with and without the LFE channel. Now if I hook up one tower to the LFE channel and the other to the Right channel the two speakers play different things in the explostions and this does not get summed if I setup my system to no sub. And the difference is not that the LFE plays louder (which it does for most) it was playing completing different information.

I spent hours double and triple checking. I was a little pissed as I spent many years just running full range with no sub.

I would of never noticed but I have watched starwars over 100 times and as I watched with a sub for the first time I was noticing sounds (new notes) Low and high at different points in the movies that were not there before. Star Wars (blyray) is mixed differently then a lot of other movies. Parts with heavy bass are NOT in the LFE like large ship fly bys or blast doors closing. The LFE is only used for explotions and the full band is used (up to 120hz). The rear channel is never used for music or rain or enviroment. The rear channel is only used for lasers, falling objects,and small sounds (1% of the movie). The side channels are used 90% of the time as music is a big part of the movie.

Disclaimer: this is only for Starwars 4,5,and 6 I did not check 1,2,3.
...prove this??

Quote:
Originally Posted by Blacklightning View Post
My Marantz SR8500 does not reroute the LFE to the main channel. I only found this out while playing Starwars with a sub I borrowed, I heard bass in new places. I ran some tests and I soon found out theLFE channel is lost with out a sub for me.
You proved that there is discrete info during Star Wars sent to the LFE channel (as is the case with most movies), you did nothing to prove that the LFE channel does not get added to the FR/L channels when the AVR is set to NO SUB.

Quote:
I was a little pissed as I spent many years just running full range with no sub.
Pissed at yourself, I'm assuming.
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post #45 of 49 Old 09-19-2014, 03:21 PM
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Blacklightning,

It is possible that it doesn't work properly but I would seriously doubt it. Almost everything does this (reroutes the LFE channel) properly. It is required for Dolby certification. Was the soundtrack you were listening to Dolby or DTS? I guess it is possible that it could properly reroute the LFE with Dolby material but not DTS.

To definitively prove that the LFE channel is (or isn't) being rerouted properly, you need something that is encoded solely in the LFE channel. The "Low Frequency Sweep, LFE" track on the AVIA calibration DVD is a track that works well for this.

I think you should send your SR8500 to me for further testing.

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post #46 of 49 Old 09-19-2014, 03:25 PM
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Originally Posted by Alan P View Post
And how does this...



...prove this??



You proved that there is discrete info during Star Wars sent to the LFE channel (as is the case with most movies), you did nothing to prove that the LFE channel does not get added to the FR/L channels when the AVR is set to NO SUB.



Pissed at yourself, I'm assuming.
Okay I will try and find a test DVD tonight that plays tones into each speaker and the LFE channel. Then I will set my system to no Sub and the LFE should be heard in the R/L speakers if you are correct.

Does that make sense?
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post #47 of 49 Old 09-19-2014, 03:59 PM
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Okay I will try and find a test DVD tonight that plays tones into each speaker and the LFE channel. Then I will set my system to no Sub and the LFE should be heard in the R/L speakers if you are correct.

Does that make sense?
Yes, provided there is something there that is truly encoded in the LFE channel and the LFE channel, only. Be aware that some calibration DVDs rely upon bass-managed bass that is encoded in the main (and SMALL) channels to calibrate the subwoofer.

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post #48 of 49 Old 09-21-2014, 12:23 PM
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Quote:
Originally Posted by sivadselim View Post
Yes, provided there is something there that is truly encoded in the LFE channel and the LFE channel, only. Be aware that some calibration DVDs rely upon bass-managed bass that is encoded in the main (and SMALL) channels to calibrate the subwoofer.
Well, I did the test and my receiver was not sending the LFE channel to the main speakers but as I was checking all my settings in all of my menus I found a LFE section that was not in my Speaker setup. And in this section I'm able to turn the LFE off, 0db, or -10dB when no subwoofer is connected. Mine was set to off, and if I change it to 0dB the LFE IS played in the mains at full volume and -10dB will play it softer to keep are speakers from getting damage at high volumes.

So you were right, my receiver does have the ability to play the LFE channel in the mains. I wish I know about this setting when I got my Marantz.
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post #49 of 49 Old 09-22-2014, 08:48 AM
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Sivadselim is (as usual) correct on all counts.

Basically a summary below:

A small setting means that speaker channel is being bass managed. It has nothing to do with physical speaker size.

A large (aka full band) setting means that speaker channel is sent a full-range signal.

For any speaker channel being bass managed, the AVR applies a high pass filter (usually 12 dB/octave) to that channel at the specified crossover frequency. It sends a duplicate signal for that channel to the subwoofer and applies a low pass filter (usually 24 dB/octave) at the specified crossover frequency. Thus forming a digital crossover. The asymmetry of the high/low pass slopes is rooted in THX protocol and is the subject for a separate discussion.

If the mains are set to large (full-band), there is normally an option which appears under the subwoofer menu called LFE+mains aka double bass, aka extra bass. When enabled, this sends a duplicate signal for the mains to the subwoofer, despite the fact the mains are already running on full range. This duplicate signal is then low-passed (usually 24 dB/octave) at the crossover frequency specified for the mains (if the AVR allows variable crossovers for each channel). If the AVR only offers one crossover for all channels, this duplicate signal is low passed at the crossover frequency for any other channels set to small.

The LFE (.1) channel is sent only sent to the subwoofer, if one is specified in the system. If a subwoofer is not specified in the system, the mains are automatically forced to large/full-range and the LFE channel is then directed to the mains. The LFE channel is never lost, even if there is no subwoofer specified.

The LPF for the LFE channel (if the AVR has this menu option) is the low pass filter frequency applied to the LFE channel. It should be set to 120 Hz. There is little channel content in the LFE channel >80 Hz, but occasionally we see something in the 100-100 Hz range.

For those experimenting with bass management, the Flight of the Phoenix sandstorm plane barrel roll bass effect (time stamp 15:38 about 4 seconds long at ~30 Hz) is exclusive to the LFE channel (at least it is on the older 480p DVD DTS track). I suspect that hasn't changed on the Blu-ray DTS HD-MA, but someone can confirm. That bass effect will be outputted by the subwoofer only if one is specified in the system. If one is not specified in the system, the mains will be forced to large/full-band and the bass effect will then be outputted from the mains.

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