# REW interpretation



## rpsamuel (Apr 16, 2011)

Hi,
I just now ran some REW tests on my home theater. Here are few graphs. I am not sure what to look ofr? Does this look normal, does anyone see an area I should focus to fix?

Thanks


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## shinksma (Aug 12, 2010)

(Massive delurk - sorry I've been AWOL...)

What you have there looks very spurious - I think if your FR truly varies from about 20dB to above 70dB then your room/system must be quite odd.

Also, you should probably post your graphs in accordance with the forum guidelines:

http://www.hometheatershack.com/forums/rew-forum/934-please-read-posting-graph.html

And finally, your measurements show that you are using a target SPL of about 52dB - that is too low for most measurements to register properly.

You probably want to review the REW instructions and re-run your tests. You should end up with a much flatter/smoother curve that bobs and floats around 50 to 80db.

Also, from my own experience I found it best to start with just the "boring" Freq Response curves and leave the Waterfall stuff to later. Otherwise you are trying to master too many new things at once and can't get your head wrapped around it all.

Just my two cents worth.

shinksma (hopefully not back to lurking)


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## rpsamuel (Apr 16, 2011)

Thanks for the input. I did the sub only this morning and hope this is in the framework of REW. I currently have Emotive UMC-1 and it runs EMO-Q to equalize. The system has a 12 band equalizer for each of the speakers.
The bands are 22, 28,35,44,56,72,89,114,141,180 and 224. I am going to get the filter readings from REQ and set it up in UMC-1. What eq filter can I use. 

I looked at BFD 1124P and I think this equalizer in UMC-1 probably does the same.

Thanks


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## shinksma (Aug 12, 2010)

OK, that looks a lot better, although you should set your graph axis limits to match the forum requirements/desirements, as noted in the link I gave you:

For a subwoofer:

VERTICAL = 45dB-105dB
HORIZONTAL = 15Hz-200Hz

That way we all interpret deviations that appear visually a certain size consistently. You can also set the target curve to more closely match what you are measuring, to provide a visual indication of what you might wish to adjust. Your axis marker values seem quite tiny in the image - maybe that gets better when you update your graph limits, or maybe that is just how it looks in the latest version of REW.

I can't comment on the EQ capabilities of the UMC-1, but your current response is fairly flat, and the null at 66-ish Hz is probably not recoverable (rooms have nodes that just swallow energy, there is usually no point in fighting them).

I assume you plugged directly into your SW, since you don't have the typical AVR cross-over drop-off at 80Hz (or wherever you set it).

You might want to run the signal through the AVR/SW combo, just to see what effect your AVR's cross-over is having. The FR in the graph you posted that is above the cross-over frequency is less relevant, since it will be filtered away from the SW.

A slight tweak upward (a boost of 3dB, width of 5Hz maybe) at 40Hz could be attempted, but I wouldn't cry if this is the final result - that is a good response curve, IMHO.

Now, rinse and repeat for main speakers (using the graph limit suggestions for full-range scan).

shinksma


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## rpsamuel (Apr 16, 2011)

Thanks for your inputs. I really appreciate it. Here is a curve through the sub with the front left & right for 20-200. It looks pretty good. I adjusted the 11 band eq that came with the system to flatten thing . I hope this looks good. Any comments? I am debating if I should get the BFD 1124 or can I use the graphic eq that came with the system. Do you thin in your opinion the BFD will makw this look and sound better.
Thanks.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Looks good - not much the BFD can do to improve that. :T

Regards,
Wayne


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## rpsamuel (Apr 16, 2011)

Thanks Wayne. Thats what I thought.


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## rpsamuel (Apr 16, 2011)

I ran the sweep from 40 to 15KHz with sub, left and right speakers. This is in graph 1. The second one shows the calibration files super imposed.

1. In the first graph I see a lot of jagged edge after 100HZ. What could cause that.
2. In the second graph note that the mike plot is inverse of my outputs. What am I doing to cause that?

Appreciate your input.

Thanks


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## JohnM (Apr 11, 2006)

rpsamuel said:


> 1. In the first graph I see a lot of jagged edge after 100HZ. What could cause that.


That is comb filtering, the effect of the direct sound summing with delayed signals reflected from the room's surfaces. At frequencies where the reflected signal is 180 degrees out of phase with the direct signal you get a cancellation and a notch in the response.



> 2. In the second graph note that the mike plot is inverse of my outputs. What am I doing to cause that?


You have saved a room measurement as a soundcard calibration, you need to clear it and then either track down the proper soundcard calibration file or do a new soudncard loopback calibration.


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## rpsamuel (Apr 16, 2011)

Based on your experience is it pretty normal? Should I correct it using some filters? Any thoughts?

Thanks


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## shinksma (Aug 12, 2010)

rpsamuel said:


> Based on your experience is it pretty normal? Should I correct it using some filters? Any thoughts?
> 
> Thanks


As JohnM mentioned, the black dotted-line graph is what REW thinks is your soundcard calibration file. It should never look like that - it should be almost flat (well within +/- 1 dB) across most of the frequency range, only varying significantly below 20 Hz and above 20kHz maybe, if it is a good soundcard. See the sample graphs in the REW online help files.

Because it is so jaggedy, JohnM's suggestion that it is a room measurement accidentally saved as a soundcard calibration seems likely. Or it is some other weird way of mis-measuring - perhaps you have the Monitor setting enabled on your soundcard, and you have a feedback situation messing it up. Whatever the source, it is a bad file and needs to be replaced.

You need to review the procedure for making and saving the soundcard calibration before you do anything else. Or, delete the soundcard calibration file and let REW assume your soundcard has perfect response - that would be a more accurate statement than using that file you have now.

By using the wrong file, REW is completely mis-interpreting the room measurements, and what you are seeing cannot be trusted at all.

And JohnM: continued thanks for the REW tool. Without it we wouldn't be here, and our audio environment would be worse for it.

shinksma


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## rpsamuel (Apr 16, 2011)

John,
First thank you for your wonderful gift to us the software. The software is facinating in what it does and encourages me to learn. As you can see I am in the learning process. I appreciate your input and Wayne who has been very kind in giving his thoughts.
Regards
Roderic


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## JohnM (Apr 11, 2006)

Difficult to say until you post a plot with the correct soundcard cal and a 45 to 105dB SPL axis range. Why did you start your sweep so high by the way, 40Hz?


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## rpsamuel (Apr 16, 2011)

Gentlemen, I calibrated the sound card and these are the new plots. Your comments please. 
I do not have a parametric equalizer. I have a graphic EQ for every speaker. For the sub the frequncy of the bands are 22, 28,35,44,56,72,89,114,141,180 and 224.

I greatly appreciate your input.
Thanks


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## JohnM (Apr 11, 2006)

Looks very good. We aim to use a 45 to 105dB range for visual consistency between plots, the span on your graphs is a little wider so they look a little flatter than they would using our usual range, but look very good in any case. If you have more than one seat it is a good idea to measure at each, otherwise an improvement at the main seat may be coming at the expense of a degradation at another and a compromise setting may be better.


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## JohnM (Apr 11, 2006)

As a PS, there is an odd dip in the soundcard cal at 1kHz, looks like some EQ was active. Any deviation from flat in the soundcard cal is reflected in the measurement, ordinarily the soundcard cal would be flat to within about 0.1dB outside the upper and lower roll-offs.


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## rpsamuel (Apr 16, 2011)

Thanks. How do I get the default scale after I played with it?


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## JohnM (Apr 11, 2006)

Click the graph "Limits" button, top right of the graph next to the Controls button.


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## rpsamuel (Apr 16, 2011)

Here is the new graphs with filters applied. Your comments will be very helpful. Thanks


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## JohnM (Apr 11, 2006)

Looks good - how does it sound?


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## rpsamuel (Apr 16, 2011)

Thats the problem. Since the changes are minimal and it happens in the sub area, I am not sure how to test or have a reference. I can say that the dialogs are clearer and the MJ's This is it sounds great. 

Question,
I see the phase graph and I am unable to understand it. Can you shed some light as to whats going on. It is straight up and down until about 80Hz and then starts waving. Why?

What other things I should look for to reduce unwanted effects?

Thanks


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## JohnM (Apr 11, 2006)

Phase is cyclic over 360 degrees, a bit like time on a clock face. The vertical lines from 180 to -180 are the wrap points, they actually represent the same value, hence the line that connects them. Phase is related to the SPL response and to time delays in the measurement, but you can ignore it when looking at EQ as it does not provide information that you make much use of.

For more general information on room responses, treatments and the like I recommend you check out the Home Audio Acoustics forum.


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## rpsamuel (Apr 16, 2011)

Here is my next set of runs on my HT. 
You can see I ran the right, left only with no sub and then altogether again. I see a lof dips on the right than th left. Is it usually like this? How should fix them? Thoughts.
Thanks for all your comments, I appreciate it.


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## JohnM (Apr 11, 2006)

Unless your room, its construction, its contents and your listening position are all perfectly symmetric the left and right responses will be different. Your combined L+R+Sub response looks great though, based on that it is difficult to see a reason for changing things.


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