The wonderful world of LFE

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jimfisheye

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These days I have to clarify that when I'm talking about surround sound systems I don't mean a soundbar, which confuses a lot of people. That should say enough about the majority of the population.
That's what bugs me about "Atmos" getting the marketing treatment. A soundbar cannot reproduce full surround program. It can only do movie soundtrack or sports broadcasts where the "surround" content is only reflections or lo-fi fx foley. It actually kind of shines for that for TV watching. I'd recommend it. Surround music is mutilated. Sorry folks but if you have a soundbar you're not only not listening to surround pretty much at all, you don't even have a good way to listen to mono or stereo in hi-fi. And you sure as hell aren't listening to 3D surround!:D I wouldn't recommend it for music at all. Not even stereo listening. Literally everything but the C channel is being ricochet off your walls and ceiling!

The wireless stuff is band limited bluetooth and not suitable for music as mentioned. There's also no reason for this obstacle. You can serve lossless 5.1 surround over an average wi-fi connection from any NAS. Or you can use any phone or tablet as a remote control via a home wi-fi network. There's no reason to try moving the mountain.

Except this was supposed to be about LFe talk...

I probably agree with the idea of using the Lfe in a mix as extension for the lowest octave and approaching with caution. I think it should be cleaned up and isolated for sure! Don't just double mix elements to the Lfe and leave the crossover in your monitor system to lo pass it! FFS...
The big fronts, no sub array with speaker managed Lfe channel to the front mains may not be the most popular surround speaker array but they're out there. A full range Lfe signal with no lo pass mixed into the fronts will alter the hell out of a mix! And then there are the encoded formats that can apparently go wild from this.
 

Owen Smith

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Big fronts in a 5.0 system with no sub is exactly my setup, I just don't have room for a sub. I have Castle Harlechs as my fronts, they're about 25 years old. I have a Castle Keep centre and Castle Richmond 3 rears. If I replaced any of them I'd have to replace the lot to get a matched system, Castle went bust over a decade ago and although the brand still exists it's a Chinese front selling different speakers with a "British" badge on them.

I find I have to tell my AV amp and Oppo 95 that I have a sub, so that the LFE channel is thrown away. If I have the LFE mixed into the fronts the bass from the Castle Harlechs is completely overwhelming.
 
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jimfisheye

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All the permutations of possible wrongs with all this really gets interesting.

It starts on some older mixing board layouts. (It's even copied in some DAW plugins.) There's a send to Lfe on the channel. The 4.0 or 5.0 goes to the mix bus assignment. So unless you insert some eq on that Lfe master, you're sending full range. And you're also doubling. But you were mixing into a subwoofer that only reproduced the low end. Usually it had a passive crossover to make sure of that. And then the mains you were using didn't have great sub bass response. So that double signal sent to both sort of split to the right place.

Now, people are supposed to look at the tools and figure it out. And some people do just that! Just pointing out how and when some of the weirdness could have started.

Then you get the consumer system weirdness.
People don't understand the 10db offset in the Lfe channel calibration. Or even what speaker management is. Sometimes it's called bass management and then someone thinks "No, I don't want to add extra bass." and ends up listening to everything really altered.

The high top + sub array is so popular that people speculate that the signals in the wires for 5.1 have any and all bass in the Lfe channel. Then they refuse to turn bass management on and miss all the bass content from all the mains channels.
 

ssully

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That approach to surround mixing is at least 20 years old, I have some 5.1 DVD-As mixed that way eg. Metallica Black Album on at least some tracks. The mixers seem to think on a cheap sound bar plus satellites the soundbar or center speaker will have better bass response so put the bass guitar in it, and put the song in left and right to get a stereo image on the satellites. I don't understand why they don't just let bass management sort these things out.
Situating the bass guitar -- and vocals and parts of drumkits -- largely in the center of the phantom image was a common mixing strategy in stereo long before surround existed. A phantom center consists of content that is shared by the left and right channels. DAW and audio editing software exploits this when the user wants to 'extract vocals' or 'extract center ' from stereo content. I've used that strategy to extract bass guitar parts from stereo recordings, to aid learning them. When they're mixed to a center (or LFE) channel in a 5.1 mix, it's even easier, of course.

Event here, though, IME the bass parts are not necessarily *only* in a single channel -- they're in the front left and right too, for example, at lower level.
 

ssully

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I am extremely happy with the output from my 3 x 12 inch powered subs for both music and movies. I have placed them so that the bass seems to be equal no matter where you sit in the room. One is in the front facing the seating and the other two are closer to the back wall facing the back wall. I have them plugged into the LFE output on the AVR and I have all the speakers set to small with a 50 hz crossover point within the AVR. I have the limiter on the subs also set to 100hz just to limit anything that is specifically sent to the LFE.
This reflects a common confusion of subwoofer out vs LFE channel.

The 'subwoofer out' of your AVR is not equivalent to the LFE channel. Nor is the 'input' jack of a subwoofer. LFE goes through these jacks, but so does bass-managed bass from other channels.

The only time that sub out/in == LFE is when you aren't using any bass management. This would be if you have 5 'full range' speakers + sub.

In either situation, there are usually two low pass filter points for LFE content.
The first filter to LFE content is the 'LPF for LFE' control of the AVR (which does NOT filter bass managed content -- that is filtered by the 'crossover' setting of the AVR).
The second filter point is typically in the subwoofer itself, its own variable crossover control for lowpassing the signal (the 'limiter' you mention), that goes from ~30 Hz to ~200Hz, or to 'none' (which removes the filter). This of course affects any signal that is coming in to the subwoofer, be it LFE alone , or bass-managed bass + LFE, or bass managed content alone (when the source has no LFE).
 

ssully

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Not all systems are properly set up, that's for sure. And as we see neither are the recordings we buy all 'properly' mixed.

Some might bristle at 'properly mixed'. I had film-based mixer dude basically scream at me on another forum that unlike for film, for music surround mixes *THERE ARE NO RULES, SO STOP ASKING WHY* . However, other information (such as Neil provided above) indicates there are industry *recommendations*, and I persist in being curious as to why mixers make this choice (full range LFE).


Someone ask Steven Wilson?
 

EricKalet

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Not all systems are alike, you know this.
Exactly why 120hz LPF setting is ideal for all systems. Let the subwoofer get all the recorded information that is being sent to it. Too many people confuse the LPF as a roll off or crossover. That's why it doesn't matter what system/speakers/etc... you have.
Screen Shot 2021-07-18 at 7.48.41 PM.png
 

Guy Robinson

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This reflects a common confusion of subwoofer out vs LFE channel.

The 'subwoofer out' of your AVR is not equivalent to the LFE channel. Nor is the 'input' jack of a subwoofer. LFE goes through these jacks, but so does bass-managed bass from other channels.

The only time that sub out/in == LFE is when you aren't using any bass management. This would be if you have 5 'full range' speakers + sub.

In either situation, there are usually two low pass filter points for LFE content.
The first filter to LFE content is the 'LPF for LFE' control of the AVR (which does NOT filter bass managed content -- that is filtered by the 'crossover' setting of the AVR).
The second filter point is typically in the subwoofer itself, its own variable crossover control for lowpassing the signal (the 'limiter' you mention), that goes from ~30 Hz to ~200Hz, or to 'none' (which removes the filter). This of course affects any signal that is coming in to the subwoofer, be it LFE alone , or bass-managed bass + LFE, or bass managed content alone (when the source has no LFE).
I believe what you are saying is how I have mine setup. Anyway it sounds fantastic so to me that's all that matters.
 

kfbkfb

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Might also be helpful, Dolby Labs assisted with this article (I still wish that the LFE content was included in the DD x.1 to [original] Dolby Surround downmix).


Kirk Bayne
 

ssully

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Exactly why 120hz LPF setting is ideal for all systems. Let the subwoofer get all the recorded information that is being sent to it. Too many people confuse the LPF as a roll off or crossover. That's why it doesn't matter what system/speakers/etc... you have.
View attachment 69178

Except, we know that there is X.1 material authored with content far beyond 120 Hz in its LFE. Audyssey here is citing film-to-DVD industry standard, specifically for Dolby and DTS audio tracks. This standard is not being adopted consistently in the music-only, DVDA/SACD/BluRay releases we buy.

And it's telling that LPF for LFE settings have options that look like this, copied from a typical Denon AVR manual:

80Hz / 90Hz / 100Hz / 110Hz / 120Hz (Default) / 150Hz / 200Hz / 250Hz
 

EricKalet

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Except, we know that there is X.1 material authored with content far beyond 120 Hz in its LFE. Audyssey here is citing film-to-DVD industry standard, specifically for Dolby and DTS audio tracks. This standard is not being adopted consistently in the music-only, DVDA/SACD/BluRay releases we buy.

And it's telling that LPF for LFE settings have options that look like this, copied from a typical Denon AVR manual:

80Hz / 90Hz / 100Hz / 110Hz / 120Hz (Default) / 150Hz / 200Hz / 250Hz
I'm curious as to what content has been authored in which the LFE has information beyond 120hz.

According to The Recording Academy's Producers & Engineers Wing - Recommendations For Surround Sound Production:
4.6.1 "Filtering the LFE Channel The subwoofer is often the most inaccurately configured component in the typical home theater system. Bass management schemes in consumer receivers vary widely, and most employ filtering after the summation of main channel and LFE information. A mixer who is not monitoring through a bass managed system can inadvertently create a mix that plays back with phase cancellation problems or even the entire loss of some low frequency information. Even in cinemas with fixed installations done by professionals, the sub can be poorly set up. As a result, it is our recommendation that the LFE channel should be low-pass filtered at 80 - 120Hz. This should be considered even if the project is destined for release on SA-CD or DVD-Audio, despite the fact that the spec does not require such filtering. Because the optimum frequency to be used is program-dependent, such filtering should be done by ear; simply experiment with different frequencies while listening carefully. In most cases, selecting a frequency between 80 and 100Hz will produce the best results. Use the steepest filter available (24dB/octave or higher), and choose one that maintains the most accurate phase correlation. While monitoring during mixing through a bass managed system is imperative, if low pass filtering of the LFE channel is not possible or desired, it can be printed full range and the job left to the mastering engineer."

(http://www2.grammy.com/pdfs/recording_academy/producers_and_engineers/5_1_rec.pdf)
 

ssully

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I'm curious as to what content has been authored in which the LFE has information beyond 120hz.
Did you not see the first post in this very thread?

Pick a mix from that list that has a YES in its last column. (Consider picking one released after 2004 -- the year your pdf dates from). Analyze/listen to the LFE in isolation, though a full range speaker/headphone. Tell us what you find.
 
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EricKalet

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Did you not see the first post in this very thread?

Pick a mix from that list that has a YES in its last column. (Consider picking one released after 2004 -- the year your pdf dates from). Analyze/listen to the LFE in isolation, though a full range speaker/headphone. Tell us what you find.
So then to your point and mine --

setting the LPF to 120hz as recommended - keeps the low frequencies in the .1 channel up to 120hz going to the sub and then setting your crossovers to 40 or 50 or 60 or 80 or 100 or 120 or whatever for your speakers will keep those frequencies either going to your sub (the lower) or to your speakers (the higher). So setting crossover at 80 means 80 and lower goes to Sub and 81 and higher goes to speakers, etc, etc. Setting the LPF to anything lower than 120 means losing information that could be present in the LFE channel. If your equipment has capability of setting LPF higher than 120hz then the risk is going to be the ability to locate the sub.

Content with full frequencies in the .1 will be bass managed.

Problem solved 100%.
 

AYanguas

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Content with full frequencies in the .1 will be bass managed.

Problem solved 100%.
Is this true?

I always thought that Bass Management applies only to the main channels. But NOT to the .1 LFE channel.

You will have a LPF for LFE channel, usually recommnded to 120Hz, that limits the high frequency for the LFE channel going to the Subwoofer speaker.

If a LFE (.1) channel contains frequency above 120 Hz it will be lost, first because of the eventual setting of LPF for LFE in the AVR, and second because the Subwoofer speaker will not reproduce the high frequencies.

Special surround mixes 6.0 (like Chesky's system) that have 6 full band channels is another thing, requirig a full band speaker for the sixth channel.
 

EricKalet

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Is this true?

I always thought that Bass Management applies only to the main channels. But NOT to the .1 LFE channel.

You will have a LPF for LFE channel, usually recommnded to 120Hz, that limits the high frequency for the LFE channel going to the Subwoofer speaker.

If a LFE (.1) channel contains frequency above 120 Hz it will be lost, first because of the eventual setting of LPF for LFE in the AVR, and second because the Subwoofer speaker will not reproduce the high frequencies.

Special surround mixes 6.0 (like Chesky's system) that have 6 full band channels is another thing, requirig a full band speaker for the sixth channel.
I think you may have answered your own question 😊 The LPF would filter out the frequencies above 120hz in the .1 content channel, so it wouldn’t matter if bass management is only being applied to the mains. Bass management for the mains, assuming set at 80hz would roll off 80 and below to the sub and 81 or higher to the mains. And to your point as well the sub would not reproduce the higher frequencies.
 
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