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#191400 - 01/10/08 01:50 AM Questions about bass management
autoboy Offline
veteran

Registered: 12/04/06
Posts: 118
Loc: Palo Alto, California
I was advised to set my m60s to 60hz, my VP100 to 90hz, and my QS8s to 90 hz. But after reading this article, it has me concerned that I should set my system to 90hz all the way around (I don't have 80hz option).

The article basically says that "In the majority of surround sound processors and receivers, FULL RANGE copies of all channels set to "Small" are combined together with the LFE channel, and the sum is low-passed. Think about that. Strictly speaking, any* such processor with a sub/sat crossover frequency set lower than 120 Hz is "discarding" the upper end of the LFE channel. THX units are NOT exempt from this. With the standard THX 80 Hz 4th order crossover, the top of the LFE channel gets chucked."

So if I set my mains to 60 hz and the center to 90, I have a gaping hole b/w 60 and 90 hz on the center, and any LFE is cut off at 60, which is quite a bit of LFE considering LFE goes to 120. What should I do and why are so many people using multiple crossovers. This site has proven in the past to be very accurate.

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#191432 - 01/10/08 10:37 AM Re: Questions about bass management [Re: autoboy]
Ajax Online   content
axiomite

Registered: 12/30/03
Posts: 6246
Loc: Cleveland, Ohio
Interesting question. I hope someone who knows can offer answers to the following (obviously I'm not that "someone" )

1. In a processor/receiver, are full range copies of all channels which are set to "Small" combined together with the LFE channel? Rather than "full range copies" of all channels being combined with the LFE channel, I have assumed that only the info below the crossover point set for each speaker was combined with the LFE channel and sent to the subwoofer.

2. If this summation (full range speaker copies/LFE) is actually low-passed, assuming you're using different crossover points for each speaker (mains at 60Hz, center at 80Hz, surrounds at 100Hz, etc.), which crossover point is used to low-pass the combined signal?

I know little about how the internals of a processor/receiver work, but I would've thought the info from the speakers below the set crossover point (say 80Hz), would be combined with all the info in the LFE channel, and sent to the subwoofer without the need for any more low-passing, or, if more low-passing was necessary, low-passed at a higher frequency (say 120Hz). LFE does stand for LOW frequency effects doesn't it?

Regardless, the article goes on to say:

"Don't panic. This has been going on since day one, and virtually nobody has noticed . . . with good reason......THX looked at an inordinate number of modern 5.1 soundtracks and guess what they found in the LFE channel: not much at all in the region of 80 Hz - 120 Hz, making their original choice of 80Hz rather fortuitous. Dolby Digital's LFE channel has a digital brick wall at 120 Hz, not a roll-off, so content creators almost always roll-off their stuff, usually somewhere around 80 Hz. Therefore, chucking the top band of the LFE is no big deal....."

OK, now I'm really confused.
_________________________
Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton

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#191437 - 01/10/08 11:50 AM Re: Questions about bass management [Re: Ajax]
autoboy Offline
veteran

Registered: 12/04/06
Posts: 118
Loc: Palo Alto, California
Yeah, you're telling me! And you have at least 5000 posts on audio forums. I have maybe 250 total. This has confused me since the first time I ever played with different crossovers for my mains. I wanted all the LFE b/w 90 and 60 to go to my mains because my SVS PB12-NSD is not so great at higher frequencies. I studied this for awhile and was never happy with the answers that I was supposed to blindly follow. I've been around long enough to know that consensus does not always mean correctness.

So far, I regard this website as being highly accurate technically. Their article on 1080p vs 1080i was very accurate and clear. I'm pretty well studied on deinterlacing and even I learned a few things over and above my own knowledge, and I never found any thing false. Then again, video and audio are two different realms...


Edited by autoboy (01/10/08 11:59 AM)

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#191440 - 01/10/08 11:57 AM Re: Questions about bass management [Re: Ajax]
jakeman Offline
aficionado

Registered: 10/03/05
Posts: 851
Loc: Toronto
Good post Jack. Keep in mind that that article was written over 5 years ago and processors have come a long way. Most recent AVRs that I know of include the full LFE. Even the article acknowledged it,

"...low-pass a copy of each main channel at the various frequencies I want and sum that with the full LFE channel?". Possible, yes, and if fact there are some SSP models which do this, but at a price: doing so inherently results in frequency response aberrations due to phase issues."

Autoboy, unless you have an older receiver/processor you should be OK.

And even with an older receiver there are often greater benefits depending on the speaker and room from crossing below if you have capable speakers. I still adhere to the principle that best results are usually obtained by crossing at 1/2 octave above where the speaker output is -3db because of the slope of the filters. Nowadays, I'm seeing more gear with variable slope settings ie 12db, 18db or 24db which allows better blending with the speakers at more crossover points.

The latter part of the quote is what bothers me in that there are people who suggest not only phase issues but intermodulation distortion is introduced in the summation. I have never been able to get a clear answer on that one. At the end of the day I've never detected audible artifacts from the summation so I suppose that is all that matters.
_________________________
John

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#191444 - 01/10/08 12:08 PM Re: Questions about bass management [Re: jakeman]
autoboy Offline
veteran

Registered: 12/04/06
Posts: 118
Loc: Palo Alto, California
My receiver is from 2002 or so. I have a Onkyo 875 on the way. This is where I first heard of the problem. Their review of the 805 states that different crossovers are bad and that even the Onkyo does not process it completely right.

"The crossover frequency can be set independently for each pair of speakers, the soundtrack's bass can be sent to both the main speakers and a subwoofer ("Double Bass" they call it), and the LFE channel can be low-passed at a different frequency from the rest of the bass being sent to the subwoofer . . . all of which we vehemently maintain are bad ideas, and we back that up in our essay on the subject: Miscellaneous Ramblings on Sub Crossover Frequencies. It is no fault to the product's performance, but it questions Onkyo's marketing decision to give the people what they think they want even though it may mean they hang themselves with it (unawares as they may be)."

This whole issue has me so confused...

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#191446 - 01/10/08 12:16 PM Re: Questions about bass management [Re: autoboy]
EFalardeau Offline
connoisseur

Registered: 08/27/07
Posts: 3270
Loc: Laval, Quebec, Canada
Actually, Onkyo recommends to leave those options off by default.
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#191447 - 01/10/08 12:19 PM Re: Questions about bass management [Re: EFalardeau]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17739
Loc: NoVA
Hmm... I thought that I was getting around this with my H/K by setting (all in the receiver, mind you) my mains to 60 Hz, my center to 100, my surrounds to 120, and the sub to 120. I figured that with that last setting, it limits the sub to receiving/outputting nothing above 120Hz from the other channels, and if I set it lower than that, I would have the dreaded hole. Am I wrong?
_________________________
I didn't do it, no one saw me, you can't prove anything.

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#191448 - 01/10/08 12:51 PM Re: Questions about bass management [Re: Ken.C]
Mojo Offline
connoisseur

Registered: 01/21/07
Posts: 3292
I am soooooo confused.

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#191451 - 01/10/08 01:16 PM Re: Questions about bass management [Re: Mojo]
Ajax Online   content
axiomite

Registered: 12/30/03
Posts: 6246
Loc: Cleveland, Ohio
 Originally Posted By: Mojo
I am soooooo confused.

It's Unanimous!!!!! \:\)

 Originally Posted By: autoboy
Yeah, you're telling me! And you have at least 5000 posts on audio forums. I have maybe 250 total.

Just a quick word about post counts. I recommend you don't put too much stock in them. It ain't the quantity, it's the quality. Just cuz I've got 5000 posts doesn't mean I've learned anything or, more importantly, that any of those 5000 posts have contained anything worth ingesting. In fact, there are a several forum members who would say none of mine have contained anything worth remembering. (I just wanted to get that in before they did )

 Originally Posted By: autoboy

So far, I regard this website as being highly accurate technically.

Well folks, we've fooled another one. ;\)
_________________________
Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton

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#191455 - 01/10/08 01:34 PM Re: Questions about bass management [Re: autoboy]
ihifi Offline
local

Registered: 10/06/06
Posts: 280
Loc: CT
My understaing is that the "LPF of LFE" only funtctions on the dedicated LFE channel, which normally should be set to 120hz, and it has no bearing on the redirected bass content, which depends on what HPF setting you apply on the other speakers.

John
_________________________
John
Our HT


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