Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 370 - AVS Forum
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Old 08-22-2014, 07:11 PM
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Originally Posted by HDgaming42 View Post
Hi guys,

I finally moved my sub to the back of the room following all the advice I got way back here, and I completed and placed my bass traps. Here are my results.

My Room Sim was unusual as it suggested the most ideal MLP to be in the dead center of the room. This was it's prediction:



My result (didn't save it) didn't look anything like that (even a 1" movement in Room Sim seems to destroy this particular prediction. I found the ideal sub placement and MLP to be with the MLP 105" into the room, center width.

Room Sim's version of this placement:



This is a bit jumbled, but stick with me if you will. Here is a comparison of no treatment (red) to two full height corner bass traps up front (green) with two tweaks*. More on that later.



Waterfalls:



purple instead of red for some reason--but corresponds to the All SPL above it.


After spending nearly a month's worth of "free time" (which wasn't a lot TBH) I guess I was hoping for a flatter response.

Here's what I found interesting and could use some advice on (actually, I'm soliciting all advice on anything you see here!!).

I have a set of double, solid core doors with air-tight gaskets to enter the room. It seems like that is messing with my response!



By opening the interior door I drop a peak by a number of dB, and raise a null. The door cavity is airtight (double wall construction all around). I've read that drilling holes between the doors to provide airflow into the wall cavities can help...but now I can't dig up that advice. I was worried this would short-circuit my soundproofing. Thoughts? Advice? Also of note, my rack's plexiglass door was creating havok, and I removed it to get to the point you see as "best result", no plexi-door and one door open.

Here's where I'm at utilizing best placement, no plexi-glass door and one door open. Also, two 7ft tall bass traps (corner chunk Roxul Safe N Sound) in the front two corners.



Where do I go from here?
Room Sim doesn't seem to be able to come up with a 2nd sub fix for this room. The back wall is problematic as it has those double doors, and a cubby for the equipment rack. There is really only four feet of treatable area on the back wall.

I'm open to all suggestions--really interested in your thoughts on drilling holes (how big, how many?) between the casing of the two double doors. Would love to be able to keep my (expensive!) plexi door for my rack too...

Feeling...defeated.

PS I tested pulling the traps away from the wall (they're free-standing) in 1" increments. I could see no benefit going beyond 1". I went all the way to 8", which was the maximum feasible in my room. My traps are faced with 6mil poly.
Bumping this for HD...hoping someone smarter than me has some good advice!

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Old 08-22-2014, 07:24 PM
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@hdgaming : The treatments seem to be making a small difference, but IIUC, you only have two bass traps, correct? Based on the waterfalls, which are showing severe bass ringing, you will need quite a few more traps to make a measurable difference. Remember, traps are most effective when they straddle a corner, not when they are placed flat on the wall. If you look at the pictures of my room (My Setup link in my sig), you will see that I use the intersection of the wall and the ceiling as spots for bass traps, as well as every available intersection of two walls, and even a ceiling cloud. It takes a ton of traps to fix a bad ringing problem--don't know if WAF is a factor, but a ton of traps is not always that visually attractive.

The frequency response is not terrible, but could be better. I have been using REW for years, and have NEVER used the room sim tool. Shows you what I think about that feature. IMO, additional subs are your best bet to improve frequency response, as well as "real" sub placement experiments (not the room sim).

I don't know what to say about the door. Personally, I would leave it alone. You have other options--more subs, better placement, more traps, room EQ, etc.
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Old 08-22-2014, 09:06 PM
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Jerry,

HDs waterfalls aren't scaled right, his lower limit is set to 25db. Should be more like 45 or 50....they'd look much better if they were scaled right.

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Old 08-22-2014, 09:15 PM
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Good catch, you are correct. HDGaming, how about some updated waterfalls? To be consistent with what we normally see, set the lower limit to 50Hz, and the time scale to 450 (not 500).
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Old 08-23-2014, 10:24 AM
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Quote:
Originally Posted by Alan P View Post
Bumping this for HD...hoping someone smarter than me has some good advice!
Quote:
Originally Posted by AustinJerry View Post
@hdgaming : The treatments seem to be making a small difference, but IIUC, you only have two bass traps, correct? Based on the waterfalls, which are showing severe bass ringing, you will need quite a few more traps to make a measurable difference.
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Originally Posted by Alan P View Post
Jerry,

HDs waterfalls aren't scaled right, his lower limit is set to 25db. Should be more like 45 or 50....they'd look much better if they were scaled right.
Thanks guys. Here are corrected waterfalls:

Before Treatment



After Treatment



Truthfully that looks MUCH better! I'm actually surprised the ringing isn't worse in a room with nothing in it but a subwoofer and two (four 1/2 height) bass traps.

It seems 50Hz is the lowest my traps are having a meaningful effect. That null in the 40s will have to be tackled with another sub I suppose? I could probably do ceiling/wall traps or a cloud trap...the rest of the room will be difficult. Hell, I'll take some pictures to show you guys what I'm working with--I appreciate the pics you've posted of your rooms. Let's me get an idea of what it takes!

Have a pretty packed weekend, so pics might not be right away. I'll be checking back for feedback regularly though.

Not sure this is of any use, but here's an after treatment Spectrogram, which I'm equally sure isn't scaled correctly.



EDIT: I just noticed that ringing got WORSE at 17Hz and 20Hz with treatment. Or maybe that's because of the open door...
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Old 08-23-2014, 10:40 AM
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I would focus on frequency response smoothness for now. The revised waterfalls don't look too bad. A suggestion on your measuring technique for the waterfalls. Ideally, you should aim for a measurement level that is approximately 40dB above your measured noise floor, which of most of us is around 50dB. If you look at the scale on the right of the spectrogram, you see a range of 39-79dB, which is the level of your measurements. I would aim for a peak of 90dB, and then use 50-100dB as the vertical scale on the Waterfall. As it is now, with such a low measurement level, the lower limit on the waterfall should be 40dB, which will alter how the graph looks significantly. Waterfalls are tricky to display, as well as to interpret.

And the tiny blip on the after waterfall at 20Hz should not cause any concern at all. It is probably not audible.
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Old 08-23-2014, 11:00 AM
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Quote:
Originally Posted by AustinJerry View Post
I would focus on frequency response smoothness for now. The revised waterfalls don't look too bad. A suggestion on your measuring technique for the waterfalls. Ideally, you should aim for a measurement level that is approximately 40dB above your measured noise floor, which of most of us is around 50dB. If you look at the scale on the right of the spectrogram, you see a range of 39-79dB, which is the level of your measurements. I would aim for a peak of 90dB, and then use 50-100dB as the vertical scale on the Waterfall. As it is now, with such a low measurement level, the lower limit on the waterfall should be 40dB, which will alter how the graph looks significantly. Waterfalls are tricky to display, as well as to interpret.

And the tiny blip on the after waterfall at 20Hz should not cause any concern at all. It is probably not audible.
Agree on all accounts

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Old 08-23-2014, 02:42 PM
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Quote:
Originally Posted by AustinJerry View Post
I would focus on frequency response smoothness for now. The revised waterfalls don't look too bad. A suggestion on your measuring technique for the waterfalls. Ideally, you should aim for a measurement level that is approximately 40dB above your measured noise floor, which of most of us is around 50dB. If you look at the scale on the right of the spectrogram, you see a range of 39-79dB, which is the level of your measurements. I would aim for a peak of 90dB, and then use 50-100dB as the vertical scale on the Waterfall. As it is now, with such a low measurement level, the lower limit on the waterfall should be 40dB, which will alter how the graph looks significantly. Waterfalls are tricky to display, as well as to interpret.

And the tiny blip on the after waterfall at 20Hz should not cause any concern at all. It is probably not audible.
Would I best go about enhancing my waterfalls by bumping my test tone to 90dB from the 75dB I have it at now?

Found a second to snap some pics of the room. WAF isn't too much of a factor here--the room is essentially my domain. I don't want things to look terrible, but finished traps look fine to me--the more the merrier. (I have yet to wrap my traps in cloth).

The walls are sealed, double drywall with green glue. I'm very reluctant to anchor anything to the walls and break that seal. Hence why I built my corner traps as free-standing (well, I tried just placing them in the corner but they collapsed as predicted).

The ceiling is double drywall, and suspended via clips and hat channel on de-coupled stringers. I'm not really sure how I would hang a cloud trap without throwing all that work away...

That said, I'm open to all suggestions. I also took a pic of the casing between the double doors. Found the reference:
Quote:
  1. Increased distance between doors will increase air pressure considerably when both doors are closed. To alleviate this pressure we recommend leaving a 1/4″-1/2″ space between the two door jambs. This 1/2″ space should be open entirely to the inside of the wall for the air pressure to enter the wall cavity when the doors are closed. All of our communicating door tests were completed with this gap in place.
http://www.soundisolationdoors.com/p...solation-door/


Seems like drilling holes shouldn't hurt if they're calling for a gap all the way around...
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Old 08-23-2014, 02:48 PM
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Okay, stupid question time...Any reason I should continue using my RS SPL meter for level setting, or can I switch over to REW's SPL meter? I have a CSL calibrated Umik-1, and I've added the factory sensitivity data.

I just got a new processor, and I have a friend who's willing to help me build some room treatment panels. it's finally time for me to get serious about measuring.
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Old 08-23-2014, 02:57 PM
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Okay, stupid question time...Any reason I should continue using my RS SPL meter for level setting, or can I switch over to REW's SPL meter? I have a CSL calibrated Umik-1, and I've added the factory sensitivity data.

I just got a new processor, and I have a friend who's willing to help me build some room treatment panels. it's finally time for me to get serious about measuring.
Just load the calibration file with the sensitivity parameter, play a test tone (the REW SPL calibration tone is a good one), adjust the AVR master volume until the REW SPL is showing 90dB on the mic at the MLP, then take the RS SPL and measure the tone by placing it next to the mic. If the RS SPL measures 90dB as well, then the sensitivity parameter in the mic's calibration file is working the way it should be. Going forward, there should be no need to use the RS SPL to calibrate the mic.

Also, note the AVR MV setting that produces the 90dB level. For future REW settings, simply choose the same MV setting and you should be good to go. For example, a MV setting of -11 produces 90dB at the MLP, with a 103dB headroom, every time.
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Old 08-23-2014, 03:02 PM
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Originally Posted by HDgaming42 View Post
Would I best go about enhancing my waterfalls by bumping my test tone to 90dB from the 75dB I have it at now?

Found a second to snap some pics of the room. WAF isn't too much of a factor here--the room is essentially my domain. I don't want things to look terrible, but finished traps look fine to me--the more the merrier. (I have yet to wrap my traps in cloth).

The walls are sealed, double drywall with green glue. I'm very reluctant to anchor anything to the walls and break that seal. Hence why I built my corner traps as free-standing (well, I tried just placing them in the corner but they collapsed as predicted).

You can re-post the waterfalls with the vertical axis of 40dB-90dB if you like. This will show a more accurate picture, given the relatively lower levels with which the measurements were taken. In the future, try and measure at 90dB, and use a 50-95dB vertical scale for the waterfall.

Thanks for the pictures. The room is rather small, but there is no reason you can't get excellent sound in a small room. What are the room measurements, by the way?

I'll repeat it again--in my opinion, the best way to smooth the frequency response would be a second sub, not additional treatments.
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Old 08-23-2014, 03:10 PM
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Quote:
Originally Posted by AustinJerry View Post
Just load the calibration file with the sensitivity parameter, play a test tone (the REW SPL calibration tone is a good one), adjust the AVR master volume until the REW SPL is showing 90dB on the mic at the MLP, then take the RS SPL and measure the tone by placing it next to the mic. If the RS SPL measures 90dB as well, then the sensitivity parameter in the mic's calibration file is working the way it should be. Going forward, there should be no need to use the RS SPL to calibrate the mic.

Also, note the AVR MV setting that produces the 90dB level. For future REW settings, simply choose the same MV setting and you should be good to go. For example, a MV setting of -11 produces 90dB at the MLP, with a 103dB headroom, every time.
I don't think I asked my question clearly enough. I'm actually talking about setting speaker trim levels. I find that my RS meter and mic match pretty well for the main channels, but have about a 5db spread on the sub. My assumption (and we know how dangerous those can be) is that the mic is more accurate, as I know it's been calibrated, and I have the sensitivity data. I just want to put the SPL meter away and start from scratch using just REW.

This is also important because I need to use SPL at the crossover point to set distance for my sub. I don't have any auto eq on my processor right now (it's coming, but I want to play now, not later ), and it would simplify everything if the RS meter can stay tucked away in it's drawer.

Does that make sense?
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Old 08-23-2014, 03:53 PM
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Once the mic is properly calibrated, it should be more accurate to set speaker trim levels than the RS SPL, especially at lower frequencies, if that is what you are asking.

But I am a bit confused. You start by talking about trims, and then you switch to talking about setting the sub delay. How are the sub trim and delay related?
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Old 08-23-2014, 04:43 PM
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Originally Posted by AustinJerry View Post
But I am a bit confused. You start by talking about trims, and then you switch to talking about setting the sub delay. How are the sub trim and delay related?
Sorry, I'm talking about multiple, barely related things in 1 post. The only way they are related is that I used SPL to set distance. I played a tone at the xover frequency through the center and sub, and set sub distance based on the highest SPL.
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Old 08-23-2014, 05:02 PM
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Sorry, I'm talking about multiple, barely related things in 1 post. The only way they are related is that I used SPL to set distance. I played a tone at the xover frequency through the center and sub, and set sub distance based on the highest SPL.
Not familiar with this procedure. The sub distance (really should be called delay) determines how well the sub integrates with the main speakers. In other words, it's a phase adjustment. Many of us play a frequency sweep 15-300Hz played through the center+sub(s), and observe the smoothness of the splice at the crossover point. The sub distance is adjusted gradually upwards or downwards, then re- measure, and continue adjusting until the splice at the crossover is flattest. If adjusting the distance for more than one sub, adjust the distance of both subs by the same amount, thus keeping the phase relationship between the subs unaltered.

Have you measured the flatness at the crossover frequency? Does it look good? If yes, then you have the delay set properly.
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Old 08-23-2014, 05:32 PM
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Not familiar with this procedure. The sub distance (really should be called delay) determines how well the sub integrates with the main speakers.
I'm using this procedure:

Subwoofer Distance Setting

Quote:
Originally Posted by AustinJerry View Post
Have you measured the flatness at the crossover frequency? Does it look good? If yes, then you have the delay set properly.
Hopefully, if I can get things to behave, I'll be posting some graphs today. I have a pretty terrible room (concrete floors, a world shape, and a huge window on the left hand side), and trying to find information on what to address, and how to address is a bit overwhelming. I'm hoping the experts in this thread can help me decide where to start, and what will be most impactful.

Last edited by Bluescale; 08-23-2014 at 06:55 PM. Reason: formatting of quotes
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Old 08-23-2014, 05:45 PM
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Quote:
Originally Posted by Bluescale View Post
I'm using this procedure:

Subwoofer Distance Setting

Have you measured the flatness at the crossover frequency? Does it look good? If yes, then you have the delay set properly.
Hopefully, if I can get things to behave, I'll be posting some graphs today. I have a pretty terrible room (concrete floors, a world shape, and a huge window on the left hand side), and trying to find information on what to address, and how to address is a bit overwhelming. I'm hoping the experts in this thread can help me decide where to start, and what will be most impactful.[/QUOTE]

It is quite possible that both procedures will yield the same results. It is interesting, because Craig John, who is in the link you provided, is the author of the procedure that I described, which is often referred to as the "Sub distance tweak". If you go to the Audyssey thread and search sub distance tweak, you will find the detailed write-up on the procedure.
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Old 08-23-2014, 06:25 PM
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I'm running into strange behavior. When I run a sweep of my sub alone, the SPL about 15db hotter than when I run a sweep using my main speaker + sub crossed over at 90hz. Is there any logical reason for that?
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Old 08-23-2014, 07:00 PM
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How are you isolating the sub? Are you turning off the mains, or are you selecting the LFE channel in HDMI?
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Old 08-23-2014, 07:33 PM
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How are you isolating the sub? Are you turning off the mains, or are you selecting the LFE channel in HDMI?
I'm selecting the LFE channel in REW. Should I do it the other way?
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Old 08-23-2014, 07:59 PM
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No. That's fine. My HDMI only supports two channels, so I can't do it that way. It's possible that the level difference has to do with the way you are measuring. Since I can't test it out, I can't be sure. The level discrepancy shouldn't affect your ability to analyze the frequency response. You are looking for flatness of the curve, not the overall level of the measurement.
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Old 08-23-2014, 08:23 PM
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In general, is it common for LFE to be 15dB hot?

I hope so, because this is driving me nuts. Level setting when I selected the sub channel from REW are so different than the level when I used my processor test tone. The other channels are similar between my processor and REW
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Old 08-23-2014, 09:34 PM
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Quote:
Originally Posted by Bluescale View Post
In general, is it common for LFE to be 15dB hot?

I hope so, because this is driving me nuts. Level setting when I selected the sub channel from REW are so different than the level when I used my processor test tone. The other channels are similar between my processor and REW
I am a little slow tonight for some reason. Check out this discussion:
Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs

As I said before, I don't use the HDMI4 setting to measure LFE, so I don't always remember that this channel has a 10dB boost applied to it. If you want to avoid this boost, then output to the left and right channels, and turn off the left and right speakers. Bass management routes the low frequencies to the subs, without the boost (assuming you are using an AVR with bass management, of course).

Sorry for the confusion.
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Old 08-23-2014, 09:36 PM
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^

To answer my own question, redirected bass from the mains is generally 10dB to 15dB quieter than a pure LEF signal:

LFE, subwoofers and interconnects explained
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Old 08-23-2014, 09:53 PM
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Or more accurately, the LFE channel has a 10dB boost. I think it is exactly 10dB, not 10-15dB.
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Old 08-23-2014, 10:35 PM
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Quote:
Originally Posted by AustinJerry View Post
Or more accurately, the LFE channel has a 10dB boost. I think it is exactly 10dB, not 10-15dB.
From the post I linked to (and I'm taking it on faith the OP know what he's talking about):

Quote:
Okay, what level should the subwoofer output be? If it were just the LFE track, then you'd expect it, as discussed above, to be 10dB lower than the other channels to fit the 10dB higher maximum LFE output.

But if the player is performing bass management, then the subwoofer output also has to contain redirected bass; this extra signal could push the signal back above its nominal limit. To prevent overloading their output, or the receiver's input, players with bass management conventionally lower the SW output by a further 5dB. (This 5dB value is specified by Dolby, see references). Sometimes this 5dB drop switches in and out depending on whether bass management is being performed (ie if any speakers are set to SMALL).

The final SW output will typically be:
SW = LFE
or:
SW = Lower5dB(LFE + Lower10dB(Redirected bass)) = Lower5dB(LFE) + Lower15dB(Redirected bass)
So, in those two cases the SW output from the player will be respectively 10dB or 15dB lower than the other channels. A receiver should offer the ability to specifically boost the SW input on its multichannel analogue interface to compensate.
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Old 08-23-2014, 10:51 PM
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Although going back and reading that, it seems to say the opposite of what I'm experiencing. I'm starting to feel kind of dense here, and I don't know if it's me or if my processor is doing something weird .
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Old 08-24-2014, 01:08 AM
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Originally Posted by HDgaming42 View Post
I just noticed that ringing got WORSE at 17Hz and 20Hz with treatment. Or maybe that's because of the open door...
Most likely just a measuring artefact (probably noise). The important information in the graph is that the overall shape of the ridges became steeper (less ringing) and more rounded (lower Q).
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Old 08-24-2014, 01:28 AM
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To clarify.... If you select channel 4 as the output then bass management is not relevant as REW is effectively the LFE channel in this case. If you sent output to channel 1 and channel 4 then the sub will see the LFE channel (+10dB) and the redirected bass from channel 1.
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Old 08-24-2014, 04:45 AM
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Originally Posted by Bluescale View Post
Although going back and reading that, it seems to say the opposite of what I'm experiencing. I'm starting to feel kind of dense here, and I don't know if it's me or if my processor is doing something weird .
My understanding is that the LFE channel in movie soundtracks on DVDs and BDs is recorded on the disc at a level 10dB below what one might expect it to be. This is because the peak LFE output is designed to be 125dbA, while the peak audio in all of the other channels is designed to be 115 dbA. By recording the LFE channel 10dB lower, it is given 10dB of headroom in the recorded audio channel. The amplifying electornics is designed to compensate by amplifying the LFE channel by those missing 10dB. (Historical note: some early DVD DTS soundtracks were accidentally mixed without that 10dB LFE decrease, causing lots of confusion.)

When you provide an audio signal over HDMI from a computer using REW, though, all of the channels are sent audio signals with the same digital amplitude, including the LFE channel. The LFE channel's signal hasn't been decreased by the expected 10dB. As a result, it comes out of the speakers 10dB louder than it should. I.e. it's the same "mistake" that was made in early DTS recording mixes.
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