Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 432 - AVS Forum
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post #12931 of 12959 Old Yesterday, 12:18 PM
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^
looks good to me

is it a deliberate target curve? it looks like -6dB from 1kHz to 20kHz and a few dB rise below that
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post #12932 of 12959 Old Yesterday, 12:20 PM
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Originally Posted by SherazNJ View Post
jerry,
I used to blocking technique just to see which one is causing the high reflection and if the material is useful. So I placed the panel right on top of center speaker half way out and took reading. Spike was still there. Then I moved the panel all they way forward on top of the speaker. Took the reading and behold. All spikes gone. See the attached image. This confirms that the material can absorb. Also since the spike didn't go away when panel was half covering, it shows that the reflection is coming from ceiling further down (I think).
I had a pesky reflection that was bouncing off the ceiling, and then off the back wall to the MLP. When you have a multiple-surface reflection, you are no longer dealing with the first point of reflection, so do what Jim recommends--move the panel around until you find the source. It always feels good when you narrow down a reflection, doesn't it?

Don't forget the back wall. The ceiling and back wall treatments provided the most improvement for me, with the side wall treatments only producing marginal improvement.
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post #12933 of 12959 Old Yesterday, 12:24 PM
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Originally Posted by GibsonES300 View Post
I've been working through this thread while trying to improve my room and system with REW and MiniDSP.

I would love some feedback about where I am so far.

Magnepan 1.7, DWM woofer, Rythmik F15HP

I appreciate any and all feedback.
Where you are depends on what your goals are.

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post #12934 of 12959 Old Yesterday, 12:24 PM
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Originally Posted by GibsonES300 View Post
I've been working through this thread while trying to improve my room and system with REW and MiniDSP.

I would love some feedback about where I am so far.

Magnepan 1.7, DWM woofer, Rythmik F15HP

I appreciate any and all feedback.
Welcome to the thread. Looks quite good, as the d00d says. Nice work. Please describe how you are using the MiniDSP, i.e. what MiniDSP do you have, what channels it is used on, what plug-in you are using etc. I am interested because I just finished my own MiniDSP project to time-align four subs using a 2x4 box.
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post #12935 of 12959 Old Yesterday, 12:25 PM
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Shouldn't that go in the miniDSP thread?

Downloadable FREE demo discs:
http://www.avsforum.com/t/1475769/de...ently-authored 

Did you really need to quote that entire post in your reply?
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post #12936 of 12959 Old Yesterday, 12:36 PM
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The target curve was deliberate. It just sounds nice to me.

I'm using a 2x4 unbalanced MiniDSP. It's running the 2.1 plugin and handling the hand-off between the 1.7's and Rythmik. I've been pretty pleased with how it works. I may look into the new Dirac unit they're releasing to get these results on the rest of my channels. My only gripe with the 2x4 is the .9V limit on the output.

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post #12937 of 12959 Old Yesterday, 12:40 PM
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Quote:
Originally Posted by AustinJerry View Post
If you find the source of the reflection, but the treatment isn't effective enough to get it below -20dB, either get more effective treatments, or be happy with the way it is.
Which one is considered an effective material? Guide points out R-30 pink stuff. I don't assume they come in panels?
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post #12938 of 12959 Old Yesterday, 01:05 PM
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Originally Posted by SherazNJ View Post
Which one is considered an effective material? Guide points out R-30 pink stuff. I don't assume they come in panels?
I dont mean to present riddles, but what material is best depends on:

1) The space available
2) Down to what frequency your trying to absorb
3) The size of the surface

Pink Fluffy is best in the sense that it absorbs the lowest when there is enough available space (12"+).

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post #12939 of 12959 Old Yesterday, 01:28 PM
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Originally Posted by jim19611961 View Post
I dont mean to present riddles, but what material is best depends on:

1) The space available
2) Down to what frequency your trying to absorb
3) The size of the surface

Pink Fluffy is best in the sense that it absorbs the lowest when there is enough available space (12"+).
Thx for that. I was disputing in my mind weather the stuff I have is effective since I saw spikes going down but not much. Then at one point, it took out the whole spike (see image at 19.20m). So then it seems like that it is working. I just don't understand why I'd see some spikes reducing to only a few dbs (like 3-4db)????? I thought that its the material but then some spikes are completely gone below -20. I'm all confused about these materials Why would they take out small spike and now whole? Could it be also the angle wave is interacting with panel?
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post #12940 of 12959 Old Yesterday, 01:52 PM
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Originally Posted by SherazNJ View Post
Thx for that. I was disputing in my mind weather the stuff I have is effective since I saw spikes going down but not much. Then at one point, it took out the whole spike (see image at 19.20m). So then it seems like that it is working. I just don't understand why I'd see some spikes reducing to only a few dbs (like 3-4db)????? I thought that its the material but then some spikes are completely gone below -20. I'm all confused about these materials Why would they take out small spike and now whole? Could it be also the angle wave is interacting with panel?
Dont confuse absorption with reflection. Using panels as per the blocking method inherantly has very high angles involved. Your panel, in such a case, is redirecting (reflecting) the sounds away from one place to another at least as much as its absorbing anything.

The other thing involved is that a panel on a wall is much further from the source than a blocking panel at the speaker. At the wall, the sound has had some time to spread out, requiring you cover a larger surface area for effectiveness, particularly as the frequency in question is lower.

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post #12941 of 12959 Old Yesterday, 03:36 PM
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Originally Posted by jim19611961 View Post
Dont confuse absorption with reflection. Using panels as per the blocking method inherantly has very high angles involved. Your panel, in such a case, is redirecting (reflecting) the sounds away from one place to another at least as much as its absorbing anything.

The other thing involved is that a panel on a wall is much further from the source than a blocking panel at the speaker. At the wall, the sound has had some time to spread out, requiring you cover a larger surface area for effectiveness, particularly as the frequency in question is lower.
Ah that makes a lot more sense now. Each time I was moving panels, I could see up/downs changing.

So guys, here is the before and After. I still couldn't get rid of reflection around 4-4/12 . What do you guys think?
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post #12942 of 12959 Old Yesterday, 04:39 PM
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Ah that makes a lot more sense now. Each time I was moving panels, I could see up/downs changing.

So guys, here is the before and After. I still couldn't get rid of reflection around 4-4/12 . What do you guys think?
Floor?

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post #12943 of 12959 Old Yesterday, 06:02 PM
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Floor?
I have basic carpet on floor. Will be putting blackest black carpet later. As of now no panels on floor but I did test by putting three panels off floor. I didn't cover area of center speaker from speaker to next 6 feet. May be that's causing it.

Another point I wanted to ask is how one can determine determine if too much reflection is absorbed? I have read in many places that we do want some reflection to keep room alive. So does that mean that we can leave some reflection above -20? Or it means to leave reflections below -20 and anything above is BADDDDDDD?
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post #12944 of 12959 Old Yesterday, 06:41 PM
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So when you tried the blocking technique, there was no direction that alleviated that massive early reflection? That is really nasty.
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post #12945 of 12959 Old Yesterday, 06:43 PM
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Originally Posted by SherazNJ View Post
I have basic carpet on floor. Will be putting blackest black carpet later. As of now no panels on floor but I did test by putting three panels off floor. I didn't cover area of center speaker from speaker to next 6 feet. May be that's causing it.

Another point I wanted to ask is how one can determine determine if too much reflection is absorbed? I have read in many places that we do want some reflection to keep room alive. So does that mean that we can leave some reflection above -20? Or it means to leave reflections below -20 and anything above is BADDDDDDD?
You may be over-thinking this. You need to identify the major reflections, find a treatment that eliminates the reflection, and then sit back and decide whether the room sounds better or not.
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post #12946 of 12959 Old Yesterday, 11:08 PM
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So when you tried the blocking technique, there was no direction that alleviated that massive early reflection? That is really nasty.
I watched "Into The Storm" today. What a great movie to test the system. I am very happy with how bass responded. Very good indeed. Can't say the same for speakers yet.

Jerry, when I covered center speaker from top by placing the panel on top of it, it eliminated every single reflection but covering ceiling is not helping so far. That's why I'm constantly questioning my material. Can someone please share a good material to use? Jim said that pink stuff (R-30) are good for low bass. What is an effective material I can use?
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post #12947 of 12959 Old Today, 03:15 AM
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Originally Posted by SherazNJ View Post
Another point I wanted to ask is how one can determine determine if too much reflection is absorbed? I have read in many places that we do want some reflection to keep room alive. So does that mean that we can leave some reflection above -20? Or it means to leave reflections below -20 and anything above is BADDDDDDD?
An unfiltered ETC doesn't tell you what frequencies make up the reflection. Furthermore lower frequency reflections don't show up as sharp spikes so there's a mismatch in how high and low frequencies get represented in the graph. A spectrogram is probably a better way of looking at reflections both in time and frequency spectrum.

Anyway, probably more important is acoustical symmetry. Make sure first strong reflections from the left and right speaker arrive at the same time. This can remove a lot of ambiguous localization cues.

If this is fixed then I would move on to eliminating very early reflections <2ms. Plants, furniture, coffee tables, chairs with high backs, equipment racks between the speakers, floor reflection, etc.

Markus

"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole

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post #12948 of 12959 Old Today, 09:58 AM
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Anyway, probably more important is acoustical symmetry. Make sure first strong reflections from the left and right speaker arrive at the same time. This can remove a lot of ambiguous localization cues.
How do we know if left and right speakers arrive at the same time?

[/QUOTE]
If this is fixed then I would move on to eliminating very early reflections <2ms. Plants, furniture, coffee tables, chairs with high backs, equipment racks between the speakers, floor reflection, etc.[/QUOTE]

I was constantly looking at impulse graph with 50ms. 2ms woowww. That's a very small time period. Changing limit to 3ms, I hardly see any reflection for center speaker (that is if I understand it correctly). All the images I'm attaching are speakers only (no sub). Center doesn't seem to have spikes. The only one I see is at 240u which is a time frame where its decaying from 0. Left speakers seems to be doing ok as well. Right one though has two major spikes. Is my understanding correct?

thx
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post #12949 of 12959 Old Today, 10:07 AM
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I covered first reflection point on ceiling. Took before and after reading and see absolutely no difference. Am I reading the graph wrong? If not then seems like the material I'm using is useless. The material I'm using is 4" Thick Roxul Mineral Wool Acoustical Board. I put that 4" in a wood panel (wood is used only to provide borders to hold the material).

I installed the panels by first measuring distance from center speaker and MLP. Then divided into half and from that point installed three panels (2 feet wide x 4 feet long). So basically there is 6 feet of area covered.

Red = With Absorber panels
Blue = Without Absorber panels.
[Sorry for the quote, I really just copied it for a reference/reply point because I had a relevant $0.01 to add.]

Instead of arranging the panels in a 6'x4' pattern, you should try a 12'x2' pattern across the room at the same half-way distance as now. I found that to be much more effective here, sonically and measurably, with a 7.1 setup (or 7.2 etc., who knows what's what re that type of designation these days, the point being there are "lots" of speakers). I know it's a real pain to move stuff around on the ceiling...

Also mount the panels ~one panel-thickness away from the ceiling, at least leave a space you can easily get your hand into; this will increase the absorption effect of the panels. 4" should be plenty thick, I use 3" panels (for now) on the ceiling and it is good, I saved the 4" panels for "something else" (for now they're semi-randomly hung on the wall in non-effective places that doesn't look bad i.e. wall storage). My panels are some type of Roxul rockwool, I forget exactly right now but the good type of their brand anyway. It's soft like fiberglass, not any type of "board".
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post #12950 of 12959 Old Today, 10:22 AM
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How do we know if left and right speakers arrive at the same time?
If this is fixed then I would move on to eliminating very early reflections <2ms. Plants, furniture, coffee tables, chairs with high backs, equipment racks between the speakers, floor reflection, etc.[/QUOTE]

I was constantly looking at impulse graph with 50ms. 2ms woowww. That's a very small time period. Changing limit to 3ms, I hardly see any reflection for center speaker (that is if I understand it correctly). All the images I'm attaching are speakers only (no sub). Center doesn't seem to have spikes. The only one I see is at 240u which is a time frame where its decaying from 0. Left speakers seems to be doing ok as well. Right one though has two major spikes. Is my understanding correct?

thx[/QUOTE]

You can observe symmetry by taking measurements of both speakers and then using the REW Overlay function to view both measurements at the same time. It helps if the two measurements are different colors.

Yes, left and center look decent, right has a couple of issues.
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post #12951 of 12959 Old Today, 10:37 AM
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[Sorry for the quote, I really just copied it for a reference/reply point because I had a relevant $0.01 to add.]

Instead of arranging the panels in a 6'x4' pattern, you should try a 12'x2' pattern across the room at the same half-way distance as now. I found that to be much more effective here, sonically and measurably, with a 7.1 setup (or 7.2 etc., who knows what's what re that type of designation these days, the point being there are "lots" of speakers). I know it's a real pain to move stuff around on the ceiling...

Also mount the panels ~one panel-thickness away from the ceiling, at least leave a space you can easily get your hand into; this will increase the absorption effect of the panels. 4" should be plenty thick, I use 3" panels (for now) on the ceiling and it is good, I saved the 4" panels for "something else" (for now they're semi-randomly hung on the wall in non-effective places that doesn't look bad i.e. wall storage). My panels are some type of Roxul rockwool, I forget exactly right now but the good type of their brand anyway. It's soft like fiberglass, not any type of "board".
Oh boy. Changing the direction is a big pain for sure. Its not only changing but also making holes and putting the holders in there. My panels are easily lower than 1 inch from ceiling. Your description of material matches mine as well. I don't know though which one is good and which one is bad. When I bought them, they came 4 panels wrapped together and each is 2x4 with 4" thickness. They are not stiff like 703 fiberglass board but not completely fluffy as well.
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post #12952 of 12959 Old Today, 10:40 AM
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Hi everyone, I hope you're all having a nice Xmas holiday.

I just wanted to post a quick update.

First of all, thanks again for the guide, it's such a fantastic resource and a great time saver.

Because I'm doing tests at the moment with my 3311 to be ready to calibrate properly when my X7200W arrives in the next couple of weeks, I'm not going to waste your time with interim measurements.

As I'm expecting XT32 to be much better than XT, it's also more efficient to see how the new Audissey can improve things.

What I've done until now is optimize my sub placement, speakers crossovers and check the effect of various pieces of furniture.

Unfortunately my room is quite small so although it is dedicated (and entirely black velvet covered) I don't have much flexibility for speaker placement or room treatment.

I used REW to decide between left corner or between FL and C for the sub (latter was much better) and also to find the best distance from the front wall for the sub. I settled for about 3 inches. I also used it to optimize the crossover for the front and centre speakers (I settled for 60Hz/small for the front and 80Hz for the centre, vs the 40Hz large/60Hz small Audissey default).

Just doing this was invaluable!

I then tried to see how I could tame some dips I had between 100Hz and 200hz on the centre speaker and it looks like they are completely connected to my recliners which feet are about 3 ft from the centre speaker when extended. That's probably going to be my biggest issue, as XT doesn't do much about it. I'm hoping XT32 will do a better job. The dips almost entirely disappear if I fold the recliners, but that's not a very realistic use.


The other issue I'm going to have to deal with is some ringing revealed by the waterfall graph but again I want to see what XT32 does with the X7200W before wasting your time with this.

The last thing I did is generate a 90 degrees file from my standard 0 degrees one following the steps outlined here: http://johnr.hifizine.com/2014/09/ho...ibration-file/. The only thing that's not needed is the last columns of zeros (phase data, not in the original calibration file and apparently not needed for REW). Also I did a few measurements for each position as I noticed that sometimes there is one measurement that is kind of astray. You don't want to use that one for either the A or M measurement.

As the 90 degrees vs 0 degrees mostly has an effect above 10KHz, I chose to position the Umik at about 1ft from the tweeter of my left front speaker, at exactly the same height as the tweeter centre (80 cm). That way the measurements were more consistent for the range above 10KHz. I had set the 3311 to direct to disable the sub and any audio processing.

Overall that was very easy, very straightforward and very efficient. I'm mainly posting this as it's a good way to generate this file for those who don't have it. As you can see it makes a BIG difference (up to 5dB) over 10KHz, and it's quite significant (up to 2-3 dB) between 1.5KHz and 5kHz.

That's the only graph I'm going to attach for now, as I'd rather save your collective wisdom and energy for when I get measurements with my X7200W, in a few weeks at most.

As the method linked above doesn't touch the calibration file below 1000Hz, I set the cursor there, so you can see the effect of the new calibration file over the default when the Umik is used at 90 degrees.

I used the same file names as in the linked article. A is the measurement with the default 0 degrees calibration file with the mike at 0 degrees, M is the measurement at 90 degrees with no calibration file (with the tip of the mike in exactly the same position as in A), and V is the verification measurement using the newly generated 90 degrees calibration file, exact same microphone position as in M.

Thanks again for all the help present in the guide, it really allows to hit the ground running. I'll post more as soon as the X7200W is here.
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post #12953 of 12959 Old Today, 10:46 AM
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Quote:
Originally Posted by AustinJerry

You can observe symmetry by taking measurements of both speakers and then using the REW Overlay function to view both measurements at the same time. It helps if the two measurements are different colors.

Yes, left and center look decent, right has a couple of issues.
I was looking for this overlay function withing Impulse response (like water fall has in its control panel). couldn't find so I was switching back and for to see the difference . Don't I feel so stupid now . Overlay (the name literally tells us) should have been the 2nd choice.

Anyway, now that I know of such function exists, here is the overlay of Left and Right. Definitely not very arriving at same time.
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post #12954 of 12959 Old Today, 12:31 PM
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@ Manni01,

Not quite sure I understood your mic placement. For typical REW measurements, your mic should be in the MLP at ear height. Is that where you placed it? And do the measurements include the sub? The low end looks pretty anemic.
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Originally Posted by SherazNJ View Post
I was looking for this overlay function withing Impulse response (like water fall has in its control panel). couldn't find so I was switching back and for to see the difference . Don't I feel so stupid now . Overlay (the name literally tells us) should have been the 2nd choice.

Anyway, now that I know of such function exists, here is the overlay of Left and Right. Definitely not very arriving at same time.
Why is the horizontal scale so narrow? Typically the scale should go to 40ms.
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@ Manni01,

Not quite sure I understood your mic placement. For typical REW measurements, your mic should be in the MLP at ear height. Is that where you placed it? And do the measurements include the sub? The low end looks pretty anemic.
This measurement was done at the FL speaker to generate the 90 degrees calibration file that I didn't have. The sub was not active. As I said in my post, I'm waiting for the X7200W to provide measurements from MLP at ear height as I don't want to waste your time with my 3311 which is to be replaced. I'm expecting XT32 on the 7200 to solve a lot of the problems I'm seeing with the 3311/XT.
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OK, I understand now. While I firmly believe XT32 does a better job than XT, it will be interested what it does for your listening room. I hope it meets your expectations.
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My understanding is that XT32 does a better job in the low end and less unneeded corrections in the high end, which is what my listening room needs.
I'm sure it won't solve everything but that way we'll see what we can do about the problems that remain (I'm sure it's won't be perfect given the imperfection of my room, speakers, MLP etc).
I'll post proper measurements from MLP as soon as I get the X7200W in.
You might want to add a link to the procedure for the 90 degrees calibration file in the guide as it's a fast, easy and economical way to generate a fairly accurate one from the standard 0 degrees calibration file.
One thing I forgot to report is that I checked the levels of all my speakers post Audissey and my SPL meter (a Panasonic SH-8000, analog vu-meter in slow) reported around 75dB for all the speakers, while REW with the Umik-1 reported a bit higher, around 77-78dB. I guess this is an acceptable margin of error, so I decided to keep the Audissey levels for now and not to touch the sensitivity parameter in the calibration file. What do you think?
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Originally Posted by AustinJerry View Post
Why is the horizontal scale so narrow? Typically the scale should go to 40ms.
Because everybody here pointed out here that the most critical is < 2ms. So I decided to handle that first and its much easier to see it when scale is narrowed down to 3/4 ms.
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