LPF of LFE Revisited - AVS | Home Theater Discussions And Reviews
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Old 03-08-2009, 03:05 PM - Thread Starter
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Just wondering if anyone has found any decent discussion or articles regarding this setting. Or if anyone can relate their specific personal experience when experimenting with this setting.

The usual recommendation for this setting is to set it to 120Hz as the LFE channel can contain info as high as that, but that if this creates any subwoofer localization issues, it can be lowered. Interestingly, though, if I am not mistaken, ONKYO, one of the first manufacturers to include this setting, defaults it to 80Hz. Also, if I am not mistaken, it is my understanding that Audyssey (or the like) does not alter this setting and that it is intended to be set manually.

I'm wondering if, maybe, the setting might address cancellation/phase issues between the LFE channel and the main channels when there is some overlap there and similar or identical content is encoded in both places. In other words, with the typical 80Hz main channel low-pass and an LFE low-pass of 120Hz, there would be an overlap between the sub's and the main speakers' output from 80Hz to 120Hz. Because of the different distances of the speakers relative to the sub, and because of the room's very different acoustic affect upon each speaker and the sub, the relative phasing of each speaker and the sub is in many cases different. If similar or identical material is encoded in both the LFE channel and the main channel(s) somewhere in this 80Hz to 120Hz range, there is a potential for some cancellation to occur.

Most receivers in the past could not separately low-pass the LFE channel and it was usually truncated at the receiver's crossover setting. Because the 80Hz crossover was so ubiquitously used (ala THX), and because the LFE channel (supposedly) has a digital brick-wall at 120Hz (as opposed to a roll-off), most engineers (supposedly) begin rolling off the LFE channel around 80Hz, anyway. So, I do not know how much of an issue this may be. But I have yet to see a definitive explanation (surprise) of this setting's use from any of the manufacturers who are obviously including this option for a reason. So, I wonder if there is more to this setting than meets the "ear".

Anyone?

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Old 03-08-2009, 03:48 PM
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I've often wondered about this myself. In effect, maybe the 120hz setting is compensating for a not so steep low pass used during mixdown in the THX standard. It would seem to me that it may be used as an aural 'cue' of sorts where the beginning of a percussive effect where localization might be preffered. As the reproduction decreases in frequency, the effect would then 'blend' into the LFE/LP mix. Just a thought.
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Old 03-08-2009, 05:26 PM
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Page 73 of the Onkyo 606 user manual says the following:

Low-Pass Filter for the LFE Channel
With this setting, you can specify the cutoff frequency of the LFE channel's low-pass filter (LPF), which can be used to filter out unwanted hum. The LPF only applies to
sources that use the LFE channel.


It also says:
This setting is not set automatically by the Automatic Speaker Setup function (see page 38).

Tha default on my Onkyo 606 is 120Hz and I've left it there.
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Old 03-08-2009, 05:37 PM - Thread Starter
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Quote:
Originally Posted by ajstan99 View Post

Page 73 of the Onkyo 606 user manual says the following:

Low-Pass Filter for the LFE Channel
With this setting, you can specify the cutoff frequency of the LFE channel’s low-pass filter (LPF), which can be used to filter out unwanted hum. The LPF only applies to
sources that use the LFE channel.

Yeah. I am not sure what "hum" they mean, though. I knew that this is what the ONKYO manual says and was going to mention that in my post, as well. I think some have speculated that the "hum" it refers to might be related to a 60Hz electrical hum. But if the "hum" they refer to is electrically induced, you would think you would want to tackle that directly instead of lowering the low-pass of the LFE channel. I am not sure if other manufacturers' manuals state this as a reason to lower the setting or not.


Quote:
Originally Posted by ajstan99 View Post

The default on my Onkyo 606 is 120Hz and I've left it there.

I also had an inkling that this might be the case with the newest ONKYOs. I think that older models defaulted it to 80Hz.

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Old 11-12-2009, 10:11 AM
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I thought I'd revive this thread in case someone has more information on the topic. I was searching for more in-depth information. I have an Integra DHC 9.9 and the manual is very vague. The working under that setting is almost identical to that mentioned about the Onkyo, no surprise.

Any idea on the pros and cons of going from say 80 to the max of 120Hz?

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Old 08-17-2012, 12:07 AM
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Guys, I need to know something (I know what the LPF of LFE setting does):

What if my AVR (Denon 2808) DOES NOT have a LPF of LFE setting? What will happen with the LFE content from 80Hz and up? Will I lose it or does it mean that when a AVR does not have the LPF of LFE option it sends all the LFE signal by default to the subwoofer without a upper filter?
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