Boundary Gain Compression (BGC) - AVS Forum
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post #1 of 40 Old 01-22-2008, 08:23 AM - Thread Starter
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Does anyone use THX Boundary Gain Compression (BGC) and is this recommended?

I sit 4 1/2 feet from back walls and 6 feet from each side wall and wasn't sure if this would be recommended in this configuration.

What are the pros and cons?
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post #2 of 40 Old 01-22-2008, 08:48 AM
 
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THX boundary gain compensation applies a specific EQ filter that rolls off the bass to alleviate the over-exaggerated low end response that takes place when a subwoofer is placed close to a wall or a boundary.

Since you have placed your subwoofer away from the room boundaries it would not necessitate the use of this feature. It will consume amplifier power to flatten the response which also means that driver excursion will increase (or decrease depending on the EQ cut involved).

--Regards,
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post #3 of 40 Old 01-22-2008, 09:01 AM - Thread Starter
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my subwoofer front faces back wall 5 inches and the side wall is 1 foot away. Will this make a difference?
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post #4 of 40 Old 01-22-2008, 09:10 AM
 
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I thought that sounded familiar, THX (BGC). (Boom) is a horrible sound to hear on a film soundtrack rather than a nice natural smooth response. Doesn’t it reduce the frequency around the 60Hz region?

Why a simple parametric EQ can do the same task. I keep the main sub bass for LFE.1 reproduction located beneath the TV with the centre channel placed above it.





http://www.thx.com/technologies/bgc.html
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post #5 of 40 Old 01-22-2008, 11:27 AM
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Seems to fly directly in the face of the idea of a house curve. Are there any published specs of the shelving this applies? That's all it is.
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post #6 of 40 Old 04-11-2008, 08:08 PM
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I have an 805. There are settings for BGC which can be enabled only if you select that you have a "THX Subwoofer". WTH is a THX subwoofer and how does this affect what the AVR is doing (processing) to the signal?
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post #7 of 40 Old 04-12-2008, 03:12 AM
 
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A subwoofer that is THX-certified is sealed and has a target slope that matches a second-order roll-off below resonance (12 dB per octave).

Hope that helps.

Kind regards ,
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post #8 of 40 Old 04-13-2008, 12:09 PM
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The "C" in BGC is compensation, not compression.

Looking at it closer, it's just a shelving filter. It's too generalized to be even considered a valid feature for most rooms/subs. In general you need some rise in the low end to compensate for human hearing insensitivity in the low end (Fletcher/Munson curves). I have a sealed sub (IB) and even with room gain it doesn't need to be shelved down.

Sorry but this is just another dumb THX feature. I really like re-eq and the timbre matching/decorrelation features are usually helpful but this one falls somewhere in the dubious to useless section.
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post #9 of 40 Old 02-21-2010, 12:17 PM
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Man, my set-up thrives on boundary gain....
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post #10 of 40 Old 02-21-2010, 12:33 PM
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Quote:
Originally Posted by croseiv View Post

Man, my set-up thrives on boundary gain....

Two-year old thread bump for that?!
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post #11 of 40 Old 02-21-2010, 12:36 PM
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Originally Posted by croseiv View Post

Man, my set-up thrives on boundary gain....

Whose doesn't? That's why a corner is always the first place to try a sub.
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post #12 of 40 Old 01-25-2011, 03:34 AM
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Quote:
Originally Posted by Jesse S View Post
The "C" in BGC is compensation, not compression.

Looking at it closer, it's just a shelving filter. It's too generalized to be even considered a valid feature for most rooms/subs. In general you need some rise in the low end to compensate for human hearing insensitivity in the low end (Fletcher/Munson curves). I have a sealed sub (IB) and even with room gain it doesn't need to be shelved down.

Sorry but this is just another dumb THX feature. I really like re-eq and the timbre matching/decorrelation features are usually helpful but this one falls somewhere in the dubious to useless section.
What exactly does Re-EQ do? I recently got a new Onkyo receiver (TX-NR708), upgrading from my HTiB HT-S6100 receiver, and I saw this feature. I tried it out and it made the sound just sound weird. What is its purpose? Dynamic EQ I always use though. Its brief description by Onkyo seems a little shaky but it seems to do the right thing. Maybe I need a word of advice on that too. One thing that does concern me about it though is that DTS 96/24 sound displays instead as regular DTS (16 bit) with it on...

Also, what receivers have timbre matching features? I didn't see any on mine. That would be really good for merging my Logitech Z-5500 speakers as the Front Wides and Highs for Audyssey DSX.

Finally, umm, I can take a guess but better to ask - what is decorrelation? Thanks.
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post #13 of 40 Old 01-25-2011, 03:44 AM
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I'm still not so clear on this functionality. It seems like it would actually do more harm than good. I don't have a THX subwoofer but from its general purpose, I don't see how that matters. I sit 10" from the back wall and 9.25' from the TV and fronts (which are against the front wall). Also, my two subwoofers are pretty much up against the wall (1-5" off). The approximate size of the room is 1,945 cubic feet. From the official brief description I read, it's recommended for 10' away from the screen in a room 2,000 square feet. That just about fits the bill but it probably less relevant. So anybody have any further ideas?

Also, is Loudness Plus worth to put on? It sounds to me like something that messes with the true nature of whatever possible mixture. It sounds to me like unbalanced added volume to surround speakers and dynamic compression which might work but, I just find the principle of that retarded. Is this something else? Thanks again!
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post #14 of 40 Old 01-25-2011, 07:31 AM
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Quote:
Originally Posted by Typhoon859 View Post

I'm still not so clear on this functionality. It seems like it would actually do more harm than good. I don't have a THX subwoofer but from its general purpose, I don't see how that matters. I sit 10" from the back wall and 9.25' from the TV and fronts (which are against the front wall). Also, my two subwoofers are pretty much up against the wall (1-5" off). The approximate size of the room is 1,945 cubic feet. From the official brief description I read, it's recommended for 10' away from the screen in a room 2,000 square feet. That just about fits the bill but it probably less relevant. So anybody have any further ideas?

Also, is Loudness Plus worth to put on? It sounds to me like something that messes with the true nature of whatever possible mixture. It sounds to me like unbalanced added volume to surround speakers and dynamic compression which might work but, I just find the principle of that retarded. Is this something else? Thanks again!

You're sitting in the middle of the room? Seat should be 38% of the room length from the back wall. http://www.realtraps.com/art_room-setup.htm
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post #15 of 40 Old 01-25-2011, 07:42 AM
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Originally Posted by bsoko2 View Post

You're sitting in the middle of the room? Seat should be 38% of the room length from the back wall. http://www.realtraps.com/art_room-setup.htm

That looks absolutely ridiculous, lol. Nobody that has a regular bedroom/living room or something would have such a layout because that takes up so much space - leaves little for other stuff. For a studio, yeah, maybe. Otherwise...

Anyway, where did you get that I sit in the middle of the room from? I wrote that I sit 10" from the back wall, lol.
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post #16 of 40 Old 01-25-2011, 09:45 AM
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Quote:
Originally Posted by Typhoon859 View Post

That looks absolutely ridiculous, lol. Nobody that has a regular bedroom/living room or something would have such a layout because that takes up so much space - leaves little for other stuff. For a studio, yeah, maybe. Otherwise...

Anyway, where did you get that I sit in the middle of the room from? I wrote that I sit 10" from the back wall, lol.

Right, 10" is not 10'!
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post #17 of 40 Old 01-25-2011, 01:49 PM
 
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Quote:
Originally Posted by JBLsound4645 View Post

I thought that sounded familiar, THX (BGC). (Boom) is a horrible sound to hear on a film soundtrack rather than a nice natural smooth response. Doesn't it reduce the frequency around the 60Hz region?

Why a simple parametric EQ can do the same task. I keep the main sub bass for LFE.1 reproduction located beneath the TV with the centre channel placed above it.





http://www.thx.com/technologies/bgc.html

Now that's a hell of a sub. But I too have wondered about the use of Boundary Gain Compensation. And more recently I've been wondering if the loudness plus feature does anything at all?
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post #18 of 40 Old 01-25-2011, 02:16 PM
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Now that's a hell of a sub.

Especially considering it's sitting under the new 2012 96" tube prototype display.

Stephen.

Chances are very good that I was drinking when I posted the above.

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post #19 of 40 Old 01-25-2011, 02:19 PM
 
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Especially considering it's sitting under the new 2012 96" tube prototype display.

No need to be mean bro.
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post #20 of 40 Old 01-25-2011, 02:21 PM
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No need to be mean bro.

It's just JBLsound's room. He went batty a long time ago.

Stephen.

Chances are very good that I was drinking when I posted the above.

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post #21 of 40 Old 01-26-2011, 01:00 PM
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Lol, guys?..

It's beginning to seem to me that nobody is 100% quite sure. Dumb feature XD Every time I see it it'll still bother me though, along with the other things I mentioned...
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post #22 of 40 Old 01-01-2013, 09:01 AM
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Doesn't the Audyssey calibration EQ the whole system anyway for flat frequency response in the seating positions?
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post #23 of 40 Old 01-01-2013, 09:30 AM
 
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Originally Posted by Blackdevil77 View Post

Doesn't the Audyssey calibration EQ the whole system anyway for flat frequency response in the seating positions?

Until one does a personally recorded RTA frequency sweep, good or bad, one will never know what kind of job Audyssey has done as each room adds it's own flavor to the SPL/Frequency graph.

(There's dreams and then there's dreams of dreams.)

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post #24 of 40 Old 01-02-2013, 12:35 PM
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Quote:
Originally Posted by Typhoon859 View Post

I'm still not so clear on this functionality. It seems like it would actually do more harm than good. I don't have a THX subwoofer but from its general purpose, I don't see how that matters. I sit 10" from the back wall and 9.25' from the TV and fronts (which are against the front wall). Also, my two subwoofers are pretty much up against the wall (1-5" off). The approximate size of the room is 1,945 cubic feet. From the official brief description I read, it's recommended for 10' away from the screen in a room 2,000 square feet. That just about fits the bill but it probably less relevant. So anybody have any further ideas?


Also, is Loudness Plus worth to put on? It sounds to me like something that messes with the true nature of whatever possible mixture. It sounds to me like unbalanced added volume to surround speakers and dynamic compression which might work but, I just find the principle of that retarded. Is this something else? Thanks again!

IDK much about loudness plus. To the extent it's really a "loudness" feature, it is intended to give you the perceived spectral balance that you'd have listening at "reference" (known for movies, utterly unknowable for music) when you listen quieter than that. As you turn down, the equal loudness curves demonstrate that the bass and high treble get subjectively quieter faster. SO at -20 dB from reference, the midrange sounds great but the bass sounds like it's been turened down 40 dB compared to midrange) and the very highs are slimilarly slighted. Compensating for that is an okay thing, but whether you need or like the partiular implementation is entirely up to you to decide and IMO, while I like what the Audyssey version does, I cannot bring myself to tell somwebody who hates it that they're "wrong."

To the extent its intended to control dynamics, it does indeed do some compression (and raise low levels into audibilty in a way different from a classical compressor) and that can be useful if you're listening quietly or have music strictly for background. Some of these things are pretty doggone transparent, at least at "lighter" settings, to my ears. But there are rare times when I can hear Audyssey's Cynamic VOlume "pumping" just like an old school compressor, and when at its heavier-duty settings, it dies affect apparent spectral abalance. If it's a minor change and allows me to watch a movie without my SO freaking out over the loud parts (DynVol on "day") it's reasonable compromise. But if I'm watching.listening seriously, at closer to reference levels, I leave the dynamic processing off . . . . It's great in appropriate cases for making the too-quiet audible and keeping huge explosions from causing divorce papers to appear at your doorstep, though.
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post #25 of 40 Old 03-27-2014, 06:46 AM
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Hey guys just figured I'd share some info since I just added $14,000 worth of "THX Ultra 2" gear to my home theater...

THX BGC has no affect on my twin subs

THX.loudness plus has no effect either

My new THX certified or Snake Oil cable as some haters call it produces 10 more db using the THX test tone pink noise and an SPL meter
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post #26 of 40 Old 04-02-2014, 08:52 AM
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Originally Posted by MKSniper View Post

Hey guys just figured I'd share some info since I just added $14,000 worth of "THX Ultra 2" gear to my home theater...

THX BGC has no affect on my twin subs

THX.loudness plus has no effect either

My new THX certified or Snake Oil cable as some haters call it produces 10 more db using the THX test tone pink noise and an SPL meter
That's quite a claim.

Can you detail your test equipment and metholodogy, the original cables and the new cables being tested, whether the connections are the same (have you swapped from RCA to something else), etc...
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post #27 of 40 Old 04-02-2014, 06:39 PM
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My equipment is all THX Ultra 2 certified except for the display, my test equipment is the SPL meter application for IOS, and the RCA cables are an $8 mediabridge and a $89 Monster Uni directional RCA.

The monster cable gives 10 more DB at every listening position with the SPL meter app. And I finally figured out how to use BGC. The manual from my sub amp says to turn it off and use the receiver but it disables it, BGC is amazing! If your room configuration is built for it, the best way to test it is with a bass heavy song instead of a movie and turn the BGC on and off. My situation actually thrives from BGC. Whether it's video games or a movie my couch moves across the floor now and the sub woofers don't sound Boomy anymore.
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post #28 of 40 Old 07-28-2014, 07:57 AM
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Quote:
Originally Posted by goneten View Post
A subwoofer that is THX-certified is sealed and has a target slope that matches a second-order roll-off below resonance (12 dB per octave).

Hope that helps.

Kind regards ,
That sounds potentially helpful. I don't understand it though, could you provide detail? What is a "second-order roll-off below resonance"? I think I understand you to mean that selecting for "THX Sub" rolls off or cuts dBs, but it would be helpful for me to have it spelled out, such as: 1-10 Hz cut by 36 dB, 10-20 Hz cut by 24 dB, etc. -- which probably does not even get close to what it does, but that is why I need it spelled out.

Also, not sure of the use of "resonance" there -- how is resonance established? If it refers to your specific room where dBs are bolstered by room characteristics, how does your processor know that info?

Thanks -- don't know if any of that makes sense to anyone, just trying to reach a point where it makes sense to me.....
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post #29 of 40 Old 07-28-2014, 08:16 AM
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Originally Posted by Emaych View Post
That sounds potentially helpful. I don't understand it though, could you provide detail? What is a "second-order roll-off below resonance"? I think I understand you to mean that selecting for "THX Sub" rolls off or cuts dBs, but it would be helpful for me to have it spelled out, such as: 1-10 Hz cut by 36 dB, 10-20 Hz cut by 24 dB, etc. -- which probably does not even get close to what it does, but that is why I need it spelled out.

Also, not sure of the use of "resonance" there -- how is resonance established? If it refers to your specific room where dBs are bolstered by room characteristics, how does your processor know that info?

Thanks -- don't know if any of that makes sense to anyone, just trying to reach a point where it makes sense to me.....
I didn't understand any of that stuff either but the best solution I've found is good ole trial and error, put in a movie with some good bass, (Avatar is a good reference) and turn the BGC on and off while moving from seat to seat until every position sounds the same. If your using a sub amp make sure it's set to THX ON / BGC ON, otherwise you won't be able to control the BGC using your receiver remote and will have to make adjustments by hand, hope that helps. My sub amp manual says to turn BGC off for it to work, I think it was a typo because OFF doesn't work lol, I called Klipsch and voiced my thoughts on their outdated user manual and told them that BGC has to be on in order to control it using the receiver. It's the same as the THX setting and being able to control the subs level using that receiver instead of the Gain knob on the sub amp.
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post #30 of 40 Old 07-28-2014, 08:25 AM
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Some of these settings are inactive, depending on what other modes are enabled in your receiver.
It's best to use a measurement mic and software like REW to see what's really going on.
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