Are movie and TV sound mixes accurate as it relates to bass and LFE going to the sub? - AVS Forum
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post #1 of 13 Old 03-28-2012, 07:45 AM - Thread Starter
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A while back, I entertained getting musical accurate subs to intergrate into my mains and a more home theater sub to handle the LFEs.

Skipping the whole issue of subs sounding accurate or not, what I came across was a comment by a respected subwoofer guy that mixes weren't what they were suppose to be. For instance, LFE was often put into the main channels which makes it impossible to keep them seperate and undergo the same bass management stuff that redirect bass would encounter.

So my question (more curiosity than anything else) are LFE signals always put correctly in the LFE channel or do they often wind up in the other 5/6/7/9/11 channels?

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post #2 of 13 Old 03-28-2012, 07:58 AM
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Quote:
Originally Posted by JimP View Post

A while back, I entertained getting musical accurate subs to intergrate into my mains and a more home theater sub to handle the LFEs.

Skipping the whole issue of subs sounding accurate or not, what I came across was a comment by a respected subwoofer guy that mixes weren't what they were suppose to be. For instance, LFE was often put into the main channels which makes it impossible to keep them seperate and undergo the same bass management stuff that redirect bass would encounter.

So my question (more curiosity than anything else) are LFE signals always put correctly in the LFE channel or do they often wind up in the other 5/6/7/9/11 channels?

IMO the LFE channel is for whatever the mixers and producer/director choose to put there so what is there is correct by definition. The existence of the LFE channel does not prevent use of the full range of the other channels so there will or may be low frequency content in those other channels. AFAIK the mixing stages have flat response to 20 Hz or below in the front three channels at least.

It appears that in many movies that have significant content below 20 Hz that content resides in channels other than LFE. If that's the way the mixers mixed it I would hesitate to call it wrong. Maybe different from what somebody else would do but we're talking about artistic decisions not technical requirements.
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post #3 of 13 Old 03-28-2012, 08:27 AM
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LFE is designed to play 10dB louder than full range channels. That assures effects such as explosions will always be louder. So, if a low frequency is put in a full range channel, it's just deep bass, not LFE. As for the comment by the "respected subwoofer guy", I don't know what he means.
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post #4 of 13 Old 03-28-2012, 08:41 AM
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The LFE channel is a specifically encoded channel. There can be plenty of low frequency content in the other channels, though, and there often is. But that is not "LFE"; it's simply "low-frequency info that is encoded in the other channels".

When an AVR is configured as having a subwoofer, the LFE channel info is routed in its entirety to the AVR's subwoofer pre-out. The low frequency info present in any other channel is subject to the bass management configuration of the AVR. If a channel is set to SMALL (or is being 'crossed-over') then any frequencies below that channel's crossover setting will also be sent to the AVR's subwoofer pre-out.

Certain low frequency content is often mixed simultaneously into both the LFE channel and another channel (or channels) in order to provide some coherency to the mix as well as some directionality to the effects. Very rarely will all the low frequency information in any particular effect be mixed solely into the LFE channel. It is almost always shared or spread across the LFE channel and some other channels. How any particular low-frequency information will be reproduced upon reproduction, no matter where it is encoded, depends upon the end-user's bass management configuration.

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post #5 of 13 Old 03-28-2012, 08:50 AM
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http://www.dolby.com/uploadedFiles/z...nal/38_LFE.pdf
It's an older document, (2000), but it explains the LFE channel, what can be recorded in it, as well as what the subwoofer output can contain.

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post #6 of 13 Old 03-28-2012, 11:23 AM
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The ".1" is a discrete channel. What was intentionally encoded is there.

The rest of "low level" frequencies are redirected accordingly based on your speakers, AVR and how you personally set up "bass management".
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post #7 of 13 Old 03-28-2012, 02:53 PM - Thread Starter
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Craig......thanks for the pdf.

It pretty much explains what I was told.

I think part of the problem is that we all equate LFE to subwoofer channel and that's not really how it works.

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post #8 of 13 Old 03-28-2012, 06:16 PM
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Sorry, but I still don't understand what point the "respected subwoofer guy" was trying to make in the original post.
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post #9 of 13 Old 03-28-2012, 10:09 PM - Thread Starter
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Point was that LFE isn't only in the subwoofer channel and that bass isn't only in the main channels.

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post #10 of 13 Old 03-29-2012, 08:21 AM
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^^
Hopefully, you can see from the posts in this thread that his point is without merit.

By definition, LFE is only in the .1 channel. The audio mixer may put complementary bass in full range channels to help with directionality. I don't see how that creates any problems, which is the suggestion in the OP. And, I don't know that anyone has ever suggested bass is only in the main channels in a 5.1 system.
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post #11 of 13 Old 03-29-2012, 09:24 AM
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Quote:
Originally Posted by JimP View Post

Point was that LFE isn't only in the subwoofer channel and that bass isn't only in the main channels.

The LFE channel is a discretely encoded channel and if you have a subwoofer connected to an AVR and configured conventionally then the LFE channel IS only present in the subwoofer channel.

You seem to be confused about the distinction between the LFE channel bass and any bass that might be encoded in any of the other channels. If you are using the term "LFE" to refer to anything except the actual LFE channel, itself, you are not using the term correctly.

It also seems you might not be fully grasping the difference between where the bass in any of the channels, including the LFE channel, is encoded at production versus where it can and might be produced upon reproduction.

Whether it is bass encoded specifically in the LFE channel or bass that is encoded in any of the other channels, it is ALL "bass" and where you reproduce that bass is dependent upon how you configure your AVR.

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post #12 of 13 Old 03-29-2012, 10:29 PM
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Quote:
Originally Posted by JimP View Post

Skipping the whole issue of subs sounding accurate or not, what I came across was a comment by a respected subwoofer guy that mixes weren't what they were suppose to be. For instance, LFE was often put into the main channels which makes it impossible to keep them seperate and undergo the same bass management stuff that redirect bass would encounter.

So my question (more curiosity than anything else) are LFE signals always put correctly in the LFE channel

Some idiots mix high-energy effects at single digit frequencies into the screen channels. If not redirected to a sub-woofer in the best case they get lost and in the worst case they run the speakers out to their mechanical limits and break them.

4 10 inch drivers running their voice coil formers into their motor back plates at the same time make a loud, scary, and expensive sounding noise.
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post #13 of 13 Old 03-30-2012, 10:39 AM
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Originally Posted by Drew Eckhardt View Post

Some idiots.............

Well, I don't know if that is a fair assessment or not. I wish we had more participants from this technical side of the industry participating in these forums. Maybe they could shed some light on the rationale in this respect.

I do know that they are supposed to mix for full-range channels. And are not supposed to bass manage the mix, although I am sure that, to some degree, this has to be done.

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