# Finally Using REW



## Sthrndream (Apr 21, 2006)

OK so I've been plotting everything manually for the last year and I finally decided enough's enough. Got a Behringer UCA-202 soundcard and started reading. Here is my first attempt at the soundcard calibration after about 2 hours of complete and utter futility. It looks good up until 2.00K mark where something seems to go horribly wrong. Am I OK to use this?


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## Sthrndream (Apr 21, 2006)

Here are the associated settings.
Sample rate: 48000Hz
-3dB points: 4.4Hz, 13.933kHz
Input device: Microphone (USB AUdio CODEC)
Input: MICROPHONE (Master Volume)
Channel: Left
Input volume: 0.266
Input RMS target: -15.0dB
Actual RMAS at 1kHz: -15.2dB
Output device: Speakers (USB Audio CODEC)
Output: Speaker
Sweep level: -15.0dB
20Hz..20kHz flatness: +0.5, -21.8dB


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

REW Help recommends the level for calibration to be between -12 and -6 dB FS. I had the same kind of problem with my Tascam US-122L that you are. Increasing the level above -6 dB FS did the trick for me; try it and see what you get.

Regards,
Wayne


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## Sthrndream (Apr 21, 2006)

Wayne I tried that and all I got was the same graph but the section after 2.00k went above and below the midline. I wish I could figure out what I'm doing wrong.


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## glaufman (Nov 25, 2007)

Did you try switching to 44kHz? Since it seems to at least get worse at HF...


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## Sthrndream (Apr 21, 2006)

Well that might have done the trick.


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## glaufman (Nov 25, 2007)

I certainly like that better!:T
Now just to make sure, leave the loopback in place and take a full range measurement... the result should be a flat line...


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## Sthrndream (Apr 21, 2006)

glaufman said:


> I certainly like that better!:T
> Now just to make sure, leave the loopback in place and take a full range measurement... the result should be a flat line...


OK I had to crank up the FS dB to -3dB to get the measurement high enough but this is what I got. What's the deal with the blue line?


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## glaufman (Nov 25, 2007)

It looks like your scan is up above 80dB... not that it's too high, but you can probably back off a little to 75dB... you can see more clearly if you change the vertical axis scale to be from +45dB to +105dB...
The blue line is REW displaying a target curve, in particular, this one shows what you might be shooting for on the response of your sub(s). You can tailor this in several ways, including setting the level (usually 75dB instead of 0), the rolloff (typically -12dB/octave or -24 dB/octave), the crossover frequency (on a sub target this will look like a -3dB point if using -12dB/oct and a -6dB point if using -24dB/oct). You also can change it to either a full range target, a bass limited target (i.e. mains only), and you can customize the shape with house curves and the like. Play around with that.

As for your scan, It looks basically ok, but I'm not sure why it rolls off on the low end... perhaps that's under the range of the soundcard cal file, in which case you'll want to limit your scans to 10?Hz and up, or at least remember to mentally adjust your curves at that low end.


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## Sthrndream (Apr 21, 2006)

Thanks Greg. 

It did say in the help files that it may rolloff below 10Hz. 

I may need some help with adjustments once I get to the actual measuring piece. Still figuring all of this out.


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## glaufman (Nov 25, 2007)

Yup... it sure does... I guess I should've known that... :whistling:onder::sad::huh::sweat::innocent::R


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## Sthrndream (Apr 21, 2006)

OK so I ran into another problem last night while trying to take some measurements. I hooked up my BFD 1124; RS Meter to soundcard In, soundcard OUT to BFD IN, BFD OUT to subs. I loaded my soundcard cal file and RS meter cal file but when I hit "measure" the pink noise was so far above 75dB it was flapping the curtains next to the subs (I would guess about 105dB). But even more interesting was REW told me the level was too low (-37dB)! I know once I get it it'll be easy after that but the learning curve is killing me. I'm thinking of pulling the BFD out and going straight from the AVR to see if that makes a difference.


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## laser188139 (Sep 19, 2009)

REW only knows the level after you perform the Calibrate SPL process. So it is not surprising that the RS meter gave you a high level, and the initial measure from REW without calibration would be different. Even if you calibrated REW on a previous run, if in the intervening days sometime adjusted the volume setting on the computer for any reason, the levels will no longer be calibrated when you start REW again. 

As described in the helpfile, you want to adjust the volume on the receiver and the output level from the computer to give you 75dB, or close enough, on the RS meter, verify the input levels to REW are adequately high without any clipping for the measurements to be valid, then perform the Calibrate SPL (button at the top of the measure screen) to calibrate the level. From that point, REW should read accurately for the rest of the run as long as no volume setting is changed anywhere in the system. 

Bill


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## Sthrndream (Apr 21, 2006)

So every time I have to calibrate the soundcard? I thought the point of saving the calibration file was so you didn't have to keep doing it? I am so confused.:scratch:
I haven't used my laptop for anything but REW over the last couple of days so nothing should have changed.


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## glaufman (Nov 25, 2007)

The soundcard calibration will stay once you've saved it, until you tell REW to switch it or disregard it. The purpose of that file is to level out the response at different frequencies.
This is different from "calibrate levels" where all you need to do, as Bill correctly described, is get measure the noise with a meter, and tell REW the noise it is hearing is at that level. It would ideally stay where it is, but since we often don't know what other people may have changed on the set up from day to day, we usually redo this easy portion every time we power up...


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## Sthrndream (Apr 21, 2006)

OK so this measurement graph looks quite different than the last one I posted.


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## Sthrndream (Apr 21, 2006)

glaufman said:


> The soundcard calibration will stay once you've saved it, until you tell REW to switch it or disregard it. The purpose of that file is to level out the response at different frequencies.
> This is different from "calibrate levels" where all you need to do, as Bill correctly described, is get measure the noise with a meter, and tell REW the noise it is hearing is at that level. It would ideally stay where it is, but since we often don't know what other people may have changed on the set up from day to day, we usually redo this easy portion every time we power up...


OK so that's the "check levels" after hitting the measure button correct? Or do I have to calibrate the RS meter even though I downloaded the calibration file?

I swear I've read the help files and I don't consider myself an imbecile but I sure feel like one.


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

Vidmaven said:


> OK so that's the "check levels" after hitting the measure button correct?


No. The Check Levels routine should have been accomplished before measurements begin.




> Or do I have to calibrate the RS meter even though I downloaded the calibration file?


The calibration file for the RS meter is merely to compensate for its inherent inaccuracies when the actual measurement takes place. It has nothing to do with setting levels.

Here’s a quick rundown of the steps needed:

1. Prepare to run the Check Levels routine (*Settings* icon, *Soundcard* tab) selecting *Check/Set Levels with Subwoofer* in the *Levels* pull down box, with the SPL meter at the listening position and the dial of the meter at *80dB* position. 

Change *Input Device Input* and *Output Device Output* from *Default* to *USB Audio*, or the name of the soundcard, if that option is available, and *Speaker* for output, and *Line In* for input. 

Begin the Check Levels routine. Ensure the *REW output VU meter* is at -12db and the *Sweep Level* at -12dB. If those fields are blank, check the two *Control Mixer Volume* boxes.

Set the *Wave Volume* at 1.000 and the *Output Volume* about ~0.500. (If those fields are blank,). 

Adjust your receivers volume control so the actual standalone Radio Shack SPL meter reads ~75db at the listening position.

Then adjust REW Input Volume to end up with -18dB on the REW input VU meter.

2. Still in the *Settings* section, run the *Calibrate SPL* routine (in the *Mic/Meter Tab*) to match REW's SPL meter to the real SPL meter to ~75dBSPL. Make sure the “C Weighted” SPL meter is checked.

3. Close *Settings* window. Run the *Set Target Level* routine (Target Settings icon to left of screen), which will set the target to ~75dB. Also, set the *Cutoff*, which is the crossover frequency you’re using

4. Run the *Measure* routine. 

5. Using the *Graph Axis Limits* icon, set the vertical scale to 45dB to 105dB and the horizontal scale for subs to 15Hz to 200Hz.


Regards,
Wayne


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## glaufman (Nov 25, 2007)

Yeah, what Wayne said... :whistling: that was a mouthful...



Vidmaven said:


> OK so that's the "check levels" after hitting the measure button correct? Or do I have to calibrate the RS meter even though I downloaded the calibration file?


Conceptually, at every step we run a "check levels" to make sure we have a signal getting through, and that it's at a proper level to give meaningful results. Before taking a sweep we run the "calibrate levels" to tell REW exactly what the magnitude of that signal means, this is calibrates the average level over a wide frequency range... this gets done periodically (generally every time we start a session or change the signal chain) because any change to any level control in the chain (on your computer, on your soundcard, in your AVR, in your EQ box, etc...) would otherwise cause an inaccuracy... But then we need to apply both soundcard and the mic cal files to account for how those devices are imperfect and therefore affect the signal level differently at different frequencies. These characteristics don't change very much over time, so we don't normally have to redo them unless we introduce other devices into the signal chain, but with those two files we take our "average" calibration and expand it to be calibrated at each frequency in the range. I hope this helps...


> I swear I've read the help files and I don't consider myself an imbecile but I sure feel like one.


No worries... take a deep breath, read my signature, and forgive yourself:T I'll admit it's not rocket science, but it IS a lot to absorb all at once... after all, if you just got it all easily, what would WE do all day long?


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## Sthrndream (Apr 21, 2006)

Thanks Wayne. I think that's the step I was missing. Calibrating the meter prior to measuring. I thought the downloaded file performed that step. Must have got lost in the translation.:rubeyes: I'll try it again tomorrow and see what happens. Time to go watch Moon.


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## Sthrndream (Apr 21, 2006)

OK so here's my first measurement from my seating position. Not sure why the level is so high. I'm sure there's something in the calibration that I missed. But aside from that how does it look? I have a long weekend so I have some time to play around and see how much better I can make it.


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## Sthrndream (Apr 21, 2006)

This is with all the speakers on;


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## glaufman (Nov 25, 2007)

Not sure why you thinnk the level is too high. It may be accurate. At any rate, it looks like your sub is running up to 20db hotter than your mains. Other than that it's not so bad, but why did the very low end flatten out when you added the mains?


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## Sthrndream (Apr 21, 2006)

glaufman said:


> Not sure why you thinnk the level is too high. It may be accurate. At any rate, it looks like your sub is running up to 20db hotter than your mains. Other than that it's not so bad, but why did the very low end flatten out when you added the mains?


I guess I thought if everything was calibrated at 75dB then the levels would be there also. Still figuring out how everything works together. I'm not sure why it flattened out when I added the mains. My mains and center have built in subs but that shouldn't effect it like that. I'm confused about the subs running that hot. I calibrate all speakers to 75dB and then bump the subs 5dB. How could they be 20dB higher? I'm going to spend sone time tomorrow taking measurements around the whole room to get an idea of where the best spots are. I'm still not sure the output levels are correct. Gonna try some tweaking. Seems like my FR is reasonably smooth though if everything is being done correctly.
_Posted via Mobile Device_


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## neumei626 (Feb 8, 2010)

Hello. Sorry to jack the thread, but one quick Q. Why is it bad to use more than like 3 filters in the BFD? BTW, I just set mine up a few days ago with dual MFWs and wow! What a difference in the SQ!


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## glaufman (Nov 25, 2007)

Vidmaven said:


> I guess I thought if everything was calibrated at 75dB then the levels would be there also. Still figuring out how everything works together. I'm not sure why it flattened out when I added the mains. My mains and center have built in subs but that shouldn't effect it like that. I'm confused about the subs running that hot. I calibrate all speakers to 75dB and then bump the subs 5dB. How could they be 20dB higher? I'm going to spend sone time tomorrow taking measurements around the whole room to get an idea of where the best spots are. I'm still not sure the output levels are correct. Gonna try some tweaking. Seems like my FR is reasonably smooth though if everything is being done correctly.
> _Posted via Mobile Device_


Hmmm... well, the first pic makes it look like room gain falsely elevating the sub at low f... but I agree, pending ringing and the like you may not have to work too hard :T



neumei626 said:


> Hello. Sorry to jack the thread, but one quick Q. Why is it bad to use more than like 3 filters in the BFD? BTW, I just set mine up a few days ago with dual MFWs and wow! What a difference in the SQ!


Not sure about "3" per se, but basically, there's a point of diminishing returns... each filter provides a little benefit in some ways, but can detract in others... every filter messes with things just a little bit... at some point the benefits aren't worth it...


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

> I'm confused about the subs running that hot.


I don’t know that you really have the subs 20 dB hot. It could be that you beyond the 200 Hz limit of the graph response is overall higher, but we just can’t see it.



> My mains and center have built in subs but that shouldn't effect it like that.


It would explain the significant rise between 40-80 Hz that the second graph shows...

Regards,
Wayne


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

neumei626 said:


> Why is it bad to use more than like 3 filters in the BFD?


It’s fine to use more than three, if your response calls for it. It’s just that some newbies tend to go overboard trying to get a picture-perfect graph, and use way more filters than they need to. Basically, any filters that are really narrow and only 1-2 dB gain are having no audible effect, so there’s no good reason to use them.

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

Vidmaven said:


> ... My mains and center have built in subs but that shouldn't effect it like that. I'm confused about the subs running that hot. I calibrate all speakers to 75dB and then bump the subs 5dB. How could they be 20dB higher? ...


I was confused for quite a while seeing a bump in my sub's response using REW, when all my speakers should have been calibrated to 75dB. Eventually I determined it came from running REW with both mains enabled. It sounds as if you, too, are driving both mains together. If you calibrate to the pair of fronts measuring 75dB at the SPL meter, each front alone is carrying a 72dB signal. These two signals, when combined into one electrically below the sub's crossover, will give a 78dB signal at the sub, +3dB higher. The 3dB difference comes from destructive interference between the two fronts across their frequency response, not present when driving a single speaker. In my case, the full range curves looked much more even, without a significant boost in the sub's range, when I measured the sub with each front individually. 

As Wayne wrote, there can be significant peaks or dips above 100Hz from reflections in the room that make this region appear higher or lower than expected. My room shows both. To look at the sub level relative to the main, you want to cover a much wider range. I would suggest at least to 2000Hz. 

Bill


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## Sthrndream (Apr 21, 2006)

OK so after playing with REW all weekend this is what seems to be the best reading at the main seat, this is using a crossover of 60Hz, mains and subs. Seems like I might need to address that 33Hz bump. No smoothing.


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## Sthrndream (Apr 21, 2006)

This is the same measurement but with all speakers running.


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

Yup, take care of that 33 Hz hump and you'll be rockin'. You might want to experiment with a house curve, though - a lot of people seem to prefer one over flat response.

Regards,
Wayne


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## Sthrndream (Apr 21, 2006)

Wayne A. Pflughaupt said:


> Yup, take care of that 33 Hz hump and you'll be rockin'. You might want to experiment with a house curve, though - a lot of people seem to prefer one over flat response.
> 
> Regards,
> Wayne


OK Wayne here's my main seat with 2 filters on the BFD, 1/3 octave smoothing and target level raised to 85dB. 


Walk me through the hard knee house curve as I believe I'm ready to try that. By the way ignore the previous couple of graphs. I realized that I was only measuring the subs in my mains and my real subs weren't running.:dumbcrazy:


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

> Walk me through the hard knee house curve as I believe I'm ready to try that.


No Problem!

1. Play a couple of sine waves @ your crossover frequency, and between 25 and 30 Hz (depending on where you want the slope to shelve), to determine your house curve slope (see house curve article, “An easy way to determine the house curve you need” heading).

2. Create and save a house curve txt file (see REW Help Files – House Curves).

3. Check Logarithmic Interpolation box in REW – “Settings” icon, “House curve” tab.

4. Measure.

5. Re-adjust the Target Curve to a good mid-way point between the peaks and depressions.

6. Manually equalize with REW’s EQ Panel to get predicted response to closely track the Target.

7. Apply filters to equalizer.

8. Re-measure to check the results. Re-Equalize if needed.

9. Listening tests – adjust house curve slope as needed to accommodate your tastes / expectations.


Regards,
Wayne


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## Sthrndream (Apr 21, 2006)

Thanks Wayne. I'm assuming I should set it up on a different pre-set so I can flip back and forth for music and movies. So far I like the current setup more for music than movies. The movies just don't seem to have the "oomph" I like. The music however is tight and defined.


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

Yeah, the ability to save and recall different settings is one of the nice things about the BFD. I like the house curve for music as well a movies; other people prefer it only for one or the other. :T

Regards,
Wayne


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## Sthrndream (Apr 21, 2006)

Does it make sense to do a regular house curve also? Since I have so many presets available.


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

No reason not to! You could also try different house curve slopes as well - say, increasing or decreasing by 2 dB or so.

Regard,
Wayne


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## Sthrndream (Apr 21, 2006)

Here's my first attempt at a hard knee house curve;


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## Sthrndream (Apr 21, 2006)

So I added dual Epik Empires into the mix and also some new seats which resulted in a different seating configuration so I re-ran REW;


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