Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 241 - AVS Forum
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post #7201 of 11036 Old 11-29-2013, 11:11 AM
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Another newb question: using an HDMI audio output, what is the easiest way to get a single-channel signal, all that REW apparently allows me to choose at a time, into the front R and L channels at the same time? I'm following Jerry's instructions for the readings he suggests taking in his document. Since I use external amps, I could use a Y-cable from a single preamp output into two amp inputs, but I'm guessing there's a neater way that I'm just not thinking about. Thanks.

What a fabulous program REW is! I'm really enjoying it, haven't done anything serious yet, playing around to become accustomed to its features. Even its room simulation seems very good, generally matches what I can hear and what my "playing around" measurements show. Gives an idea of what could be made better without a lot of moving gear/seats around, I imagine.

I suppose one more thing of curiosity is do most of you point your microphone straight up when measuring, like for Audyssey? My UMIK-1 is only "calibrated" for straight-on measurements, but above ~25Hz there's not much diff here in readings between straight up and straight-on*, 2.4dB at worst in only a couple of small ranges, and usually much less, but I'd like to do it like most others here so I can follow your results and corrective actions. I have read of apparently experienced "acousticians" doing it either way, but then I don't know what kind of environment or purpose they're doing it for, like if it's for a recording booth or studio, or a home living room etc.

*Edit: which I guess doesn't mean much because there's no "calibration" for straight up
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post #7202 of 11036 Old 11-29-2013, 11:48 AM
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^^ Whether it is a Radio Shack SPL or a Behringer EMC8000 for REW, I always point the mic toward the speaker, keeping the diaphragm in the same position. Except for subs, then it does not matter.
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post #7203 of 11036 Old 11-29-2013, 12:59 PM
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^ Thanks.

I don't know if you do this, but one of Jerry's suggestions is a reading of front L + R + sub(s). If you were doing that, would you point the mike towards the middle of the speakers i.e. probably straight ahead? I was hoping you'd say "point the mike straight up", so then I wouldn't have to ask that last part... smile.gif
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post #7204 of 11036 Old 11-29-2013, 01:59 PM
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Quote:
Originally Posted by cfraser View Post

Another newb question: using an HDMI audio output, what is the easiest way to get a single-channel signal, all that REW apparently allows me to choose at a time, into the front R and L channels at the same time? I'm following Jerry's instructions for the readings he suggests taking in his document. Since I use external amps, I could use a Y-cable from a single preamp output into two amp inputs, but I'm guessing there's a neater way that I'm just not thinking about. Thanks.

What a fabulous program REW is! I'm really enjoying it, haven't done anything serious yet, playing around to become accustomed to its features. Even its room simulation seems very good, generally matches what I can hear and what my "playing around" measurements show. Gives an idea of what could be made better without a lot of moving gear/seats around, I imagine.

I suppose one more thing of curiosity is do most of you point your microphone straight up when measuring, like for Audyssey? My UMIK-1 is only "calibrated" for straight-on measurements, but above ~25Hz there's not much diff here in readings between straight up and straight-on*, 2.4dB at worst in only a couple of small ranges, and usually much less, but I'd like to do it like most others here so I can follow your results and corrective actions. I have read of apparently experienced "acousticians" doing it either way, but then I don't know what kind of environment or purpose they're doing it for, like if it's for a recording booth or studio, or a home living room etc.

*Edit: which I guess doesn't mean much because there's no "calibration" for straight up

 

Not sure I am understanding the question.  To output a signal to one channel, say the left speaker, simply choose HDMI 1 in the Output drop-down on the Preferences screen.  Am I misunderstanding your question?

 

The REW measurement mic should be pointed towards the ceiling for the typical room response frequency measurements.  If you purchased the mic from Cross Spectrum Labs, you would have a 90-degree calibration file.  If you didn't purchase from CSL, then you only have a zero-degree calibration file, but don't worry, the differences between the two has been shown to be minor.  Regardless, point the mic towards the ceiling.

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post #7205 of 11036 Old 11-29-2013, 05:19 PM
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^ Thanks Jerry. Funny about that mike pointing thing, different opinions/methods, I guess that's just the way it is. I did compare the two pointings and didn't think it would make much diff from what I could see based on my limited measurements, but wanted to see what the other guys did. Cross Spectrum Labs didn't have any UMIK-1s at the time, no ETA, and the "other" calibrated mike you recommended (forget the name) they don't ship outside the U.S. so I went straight to miniDSP. Been putting off using REW long enough, so steamed ahead even if not in the preferred way.

What I was getting at is I want to do the measurements where you say to measure the left and right speakers and the sub simultaneously. My problem is I don't see an obvious way to get an HDMI audio signal into both the front L and R channels at the same time using REW. I could use a Y-cable to split the L (say) preamp out to the L and R amp inputs. What if I was using the internal amps? There must be another way... Sorry if I seem a dolt about this but it's not something I've ever done before, or even thought of doing (I always play stereo sources on my stereo system, which has a Mono switch, for mono LPs etc.). I was just thinking while typing this that I think I have a sound mode that will take a Center channel signal and output it on all channels. That could work if it does what I think, I would just leave the amps for all the channels except the front L and R turned off.

What do you do? Or am *I* mistaking what measurement I think you said to do?
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post #7206 of 11036 Old 11-29-2013, 06:02 PM
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Quote:
Originally Posted by cfraser View Post

I don't know if you do this, but one of Jerry's suggestions is a reading of front L + R + sub(s). If you were doing that, would you point the mike towards the middle of the speakers i.e. probably straight ahead? I was hoping you'd say "point the mike straight up", so then I wouldn't have to ask that last part... smile.gif
I never measure more than one speaker at a time. Not sure what I'd be looking for.
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post #7207 of 11036 Old 11-29-2013, 06:23 PM
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Originally Posted by cfraser View Post

^ Thanks Jerry. Funny about that mike pointing thing, different opinions/methods, I guess that's just the way it is. I did compare the two pointings and didn't think it would make much diff from what I could see based on my limited measurements, but wanted to see what the other guys did. Cross Spectrum Labs didn't have any UMIK-1s at the time, no ETA, and the "other" calibrated mike you recommended (forget the name) they don't ship outside the U.S. so I went straight to miniDSP. Been putting off using REW long enough, so steamed ahead even if not in the preferred way.

What I was getting at is I want to do the measurements where you say to measure the left and right speakers and the sub simultaneously. My problem is I don't see an obvious way to get an HDMI audio signal into both the front L and R channels at the same time using REW. I could use a Y-cable to split the L (say) preamp out to the L and R amp inputs. What if I was using the internal amps? There must be another way... Sorry if I seem a dolt about this but it's not something I've ever done before, or even thought of doing (I always play stereo sources on my stereo system, which has a Mono switch, for mono LPs etc.). I was just thinking while typing this that I think I have a sound mode that will take a Center channel signal and output it on all channels. That could work if it does what I think, I would just leave the amps for all the channels except the front L and R turned off.

What do you do? Or am *I* mistaking what measurement I think you said to do?

 

Open the Preferences screen:

 

 

In the "Timing Reference Output" drop-down, select "HDMI Out 2".  This will output a signal to both HDMI Out 1 (the left channel) and HDMI Out 2 (the right channel) simultaneously.

 

Remember, measuring left+right+subs is really only valid for the low frequencies (300Hz and below).  For full-range measurements up to 20KHz, it is better to measure left+subs and right+subs independently.

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post #7208 of 11036 Old 11-30-2013, 12:43 AM
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Originally Posted by Roger Dressler View Post

I never measure more than one speaker at a time. Not sure what I'd be looking for.

You'd looking for smoothness of frequency response around the crossover frequency and below. Getting L+R+sub right is probably more important than getting single speakers right because for low frequencies L+R+sub is what we listen to most of the time especially if content is music.

Markus

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post #7209 of 11036 Old 11-30-2013, 12:50 AM
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You'd looking for smoothness of frequency response around the crossover frequency and below. Getting L+R+sub right is probably more important than getting single speakers right because for low frequencies L+R+sub is what we listen to most of the time especially if content is music.
Cannot the main/sub splice smoothness be determined one channel at a time?
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post #7210 of 11036 Old 11-30-2013, 12:59 AM
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Cannot the main/sub splice smoothness be determined one channel at a time?

It can IF the measurements were made with a timing reference (so they can be summed in magnitude and phase) but this is exactly what the USB mic/HDMI REW setup is missing. Exacly the reason why I don't use it.

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post #7211 of 11036 Old 11-30-2013, 01:13 AM
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It can IF the measurements were made with a timing reference (so they can be summed in magnitude and phase) but this is exactly what the USB mic/HDMI REW setup is missing. Exactly the reason why I don't use it.
What has timing got to do with it? The main/sub relationship is not varying once it is set. Why would I want to sum anything?
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post #7212 of 11036 Old 11-30-2013, 01:36 AM
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What has timing got to do with it? The main/sub relationship is not varying once it is set. Why would I want to sum anything?

Without a timing reference REW doesn't know about the real delay of the measured system(s). There can be varying delays within the computer and sound card. Having a timing reference eliminates any errors caused by such varying delays.

Phase response of mains and sub within the crossover region varies. So even if the magnitude responses of the slopes match, the summed response won't be flat. That's why you want to look at summed responses and optimize them.

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post #7213 of 11036 Old 11-30-2013, 01:41 AM
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If I'm treating the sub and the main as one complete "speaker," there is no need to sum anything. The summing happens acoustically, just as in real use.
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post #7214 of 11036 Old 11-30-2013, 01:50 AM
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Originally Posted by Roger Dressler View Post

If I'm treating the sub and the main as one complete "speaker," there is no need to sum anything. The summing happens acoustically, just as in real use.

First you have to create that "one" sub/satellite speaker (in fact multiple "one" speakers: L+sub, C+sub, R+sub, etc). How do you do that?

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post #7215 of 11036 Old 11-30-2013, 01:58 AM
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First you have to create that "one" sub/satellite speaker (in fact multiple "one" speakers: L+sub, C+sub, R+sub, etc). How do you do that?
Bass management.
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post #7216 of 11036 Old 11-30-2013, 02:06 AM
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Bass management.

If we were in a free field then simply matching slopes of sub and satellites would give optimal results. But we use our speakers in rooms and those speakers no longer sum the way they do in a free field. That's where optimizing single and summed acoustical responses comes in.

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post #7217 of 11036 Old 11-30-2013, 02:43 AM
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If we were in a free field then simply matching slopes of sub and satellites would give optimal results. But we use our speakers in rooms and those speakers no longer sum the way they do in a free field. That's where optimizing single and summed acoustical responses comes in.
I do not care about the individual contributions of the sub and the main (unless I am troubleshooting). I care about them as in real use, operating together, in my room. So that's how I measure. I like to keep things simple. smile.gif
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post #7218 of 11036 Old 11-30-2013, 02:49 AM
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Originally Posted by Roger Dressler View Post

I do not care about the individual contributions of the sub and the main (unless I am troubleshooting). I care about them as in real use, operating together, in my room.

So do I.
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I like to keep things simple. smile.gif

I like to keep things simple as possible but complex as necessary.

Markus

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post #7219 of 11036 Old 11-30-2013, 08:59 AM
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Thanks for the help/advice guys. I had no idea what the Timing Reference Output was for exactly, but now I know of two uses for it...never would have thought one use was for a second HDMI audio signal. I take it from one of Markus' comments that it's not much good for an actual timing reference with HDMI, but that would probably be beyond my requirements and even my REW expectations at this stage.

I am not trying to get any "exact" results from the measurements. I just want to see what the room problems are, get enough info to move or set up the sub(s) and (secondarily) the mains better, and to see what acoustic treatments I could do within my budget/space confines.

I have a very tight setup in this modest room (12'x18'x9' high), tight in that there's not a lot of room to move many system components and still maintain both a proper HD viewing distance to the 60" display, but also (and more importantly for me) maintain a decent sound field at the MLP (mine) for both music and movies.

I listen in the mains' near field (barely) which I seem to prefer, and the other arrangement-confounding issue is my mains are Maggies (I like the stereo music sound field/stage) which absolutely must be far from walls (especially front wall) or they're IMO almost pointless. When you draw a map of all these space requirements there's a very limited envelope of placement. But using REW to actually measure, there may (probably will) be an arrangement and/or treatment that sacrifices a bit here and gains a lot there = overall improvement without being too "fussy" and inconvenient to live with.

Firstly I am going to sort the sub(s). I think I am having difficulty wrapping my head around using either one or two subs with SubEQ HT. I actually prefer it with one sub at this point, so clearly I need to get some hard data to better integrate the second sub because I have lots of connection/setup/placement options for the subs at least, and going by ear and simple SPL measurements has not been enough for optimal setup.
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post #7220 of 11036 Old 11-30-2013, 10:28 AM
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When you draw a map of all these space requirements there's a very limited envelope of placement.
Can you draw a map of your room and post it? (If you've already done so, can you link to it?)

Sanjay
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post #7221 of 11036 Old 11-30-2013, 11:10 AM
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I have a very tight setup in this modest room (12'x18'x9' high)

Firstly I am going to sort the sub(s). I think I am having difficulty wrapping my head around using either one or two subs with SubEQ HT. I actually prefer it with one sub at this point, so clearly I need to get some hard data to better integrate the second sub because I have lots of connection/setup/placement options for the subs at least, and going by ear and simple SPL measurements has not been enough for optimal setup.
Is your room enclosed or with openings? My sealed room is 1' smaller in each dimension (11.5, 17, 8) and was quite horrible for bass quality with a single sub, regardless of where I put it. I sit in the middle wrt the side walls, and 10' from front wall.

Even though I went for the Hsu quad pack, which works wonders, from a response perspective I could have got the same results with a pair, one front and one back. The corners are occupied so they are 1/4 away from the side walls. I'll be interested to see what you find with REW in your room.

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post #7222 of 11036 Old 11-30-2013, 12:45 PM
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^ Sanjay: let me do an up-to-date (computer) drawing instead of scanning my paper scrawls. I could use that anyway, right now, and reference it in my future REW measurement notes area if/when I move anything.

Roger: I agree about the one sub. The "one" I'm speaking of is an SVS PC13-Ultra. The other week (before I got the UMIK mike) I did the "sub crawl" again with that sub in the MLP, and even though the sub is in the "best" place as far as I could tell and balancing compromises (i.e. not via REW), the bass is crazy different all over the room. As expected. To be honest, I'm the only one who cares and I sit at the MLP (which makes it the MLP).

Both subs are in diagonally opposite corners of the room; not exactly the corners, about 2' along the wall in, and about 1' out. I have had both these subs for numerous years. I'm not a bass freak, but it would be nice to use the big sub most effectively, and to integrate the second sub only if it actually helps (since it's there...). From what I've read, you can do a good job with two subs if set up properly, three subs by some accounts, but returns diminish after that in our size of room. My "second" sub was bought mainly for music, when DVDs were just starting getting going, and it's kinda useless much below 30Hz (unmeasured, only by ear = unreliable). Point is it's not identical to the first sub, and has a lesser low end. Both subs are used sealed, which I generally prefer, but the SVS one can be put back to ported if helpful.

The room is not sealed. There is a regular-width open doorway near one back corner, and a much wider open entranceway on the same wall at the front end (yeah, soon I will ask about that, in the correction phase).

I sit (the MLP) in the middle wrt the side walls, and 11' from the front wall.

I have not done any REW measurements with subs yet.
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post #7223 of 11036 Old 12-02-2013, 01:22 PM
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^^ If I had a pair of dissimilar subs, based on my measurements, I'd put the better sub in front and the lesser one in the rear, where the contribution < 30 Hz is not of much value.

I have seen rooms where the opposite arrangement would be the better choice -- it depends on the room and seating position. So we'll just stand by until your data is available.
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post #7224 of 11036 Old 12-02-2013, 02:38 PM
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^ Sorry, didn't expect you to be so anxiously waiting. smile.gif Here's the layout with just the layers showing the speakers. The "big" sub is the one at the front, the "small" one is the one in the back. I can turn on other layers to show more stuff (furniture, TV, seats, rack/gear, etc.) if that helps. Mostly I just needed the other stuff shown for my own needs I think.
HTRoom-Speakers.jpg 121k .jpg file

Since I said the room was kind of "tight", I guess you need the whole pic. Surround speakers are mounted on the walls and the center is on an ~1' high stand.
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Been spending the last few days doing sub movements and measurements trying to address a huge spike in the FR right @30Hz. Apparently, that's the resonant frequency of a lot of stuff in my room. I can feel the half wall vibrating sympathetically. Is there anything I can do about that besides swaddle it with 10ft of rockwool?

As I walk around the room I can "hear" a null in the 30-40 Hz range. Ideally, I would place a sub right there? Unfortunately, I cannot because it's dead center in the room.

Is there any good information about the tradeoffs between addressing decay time vs flatter FR? As I was moving the sub there was clearly a place where the FR is flatter but the waterfall was worse.
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post #7226 of 11036 Old 12-03-2013, 07:38 AM
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Been spending the last few days doing sub movements and measurements trying to address a huge spike in the FR right @30Hz. Apparently, that's the resonant frequency of a lot of stuff in my room. I can feel the half wall vibrating sympathetically. Is there anything I can do about that besides swaddle it with 10ft of rockwool?

As I walk around the room I can "hear" a null in the 30-40 Hz range. Ideally, I would place a sub right there? Unfortunately, I cannot because it's dead center in the room.

Is there any good information about the tradeoffs between addressing decay time vs flatter FR? As I was moving the sub there was clearly a place where the FR is flatter but the waterfall was worse.

What are your room dimensions?

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post #7227 of 11036 Old 12-03-2013, 07:48 AM
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Originally Posted by jim19611961 View Post

What are your room dimensions?

Approx 28x28x9 (ignoring the drop ceiling). It's an odd shape so not completely square. IIRC sdurani said one of the modes will be in the 40-50Hz range so I thought I would be able to address the spike at 30Hz through sub placement.
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post #7228 of 11036 Old 12-03-2013, 08:03 AM
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Quote:
Originally Posted by artur9 View Post

Approx 28x28x9 (ignoring the drop ceiling). It's an odd shape so not completely square. IIRC sdurani said one of the modes will be in the 40-50Hz range so I thought I would be able to address the spike at 30Hz through sub placement.

http://www.mh-audio.nl/sg.asp

This ^^^^ will calculate your room modes.

With the width and length being the same, your going to have your work cut out for you. Looks to me like 60hz will be the biggest issue given you have axial modes for L W H at 60, 60 and 62hz. And again around 120hz.

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post #7229 of 11036 Old 12-03-2013, 06:28 PM
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Been a while since we've had some charts.

This is the result of moving one of my subs around. I have 3, two passives and an Outlaw M-8. Previously, I found that the M-8 best smoothed response by being right behind the MLP. Sadly, the MLP is right at a null. I thought putting the sub along the left hand wall at the null might have salubrious effect.

What do you all think?

Here's FR.


And here are the waterfalls for the above measurements.

BEFORE:

AFTER:

And here is the waterfall without the M-8.

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post #7230 of 11036 Old 12-03-2013, 08:15 PM
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"Before" and "after" what?  Moving around?  "After" looks clearly better.

 

I think the Outlaw is making a positive contribution to the overall frequency response,  With the exception of 30Hz, the waterfalls don't look bad at all.

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