# Check Level Error: Low levels



## rafa1552 (Jan 30, 2010)

Hi,
I am new to REW and having trouble getting a measurement. I have a galaxy CM-140 spl meter and UC202A external soundcard. I ran the appropriate calibrations in the settings for the soundcard and spl meter per the REW help page. But, when I attempt to run a check level on the measure screen, I get levels around -29db and a levels too low message. I am wondering if it is the connection between the spl meter (3.5mm jack) and the soundcard input (RCA). I currently have a 3.5mm male to two rca male cable connecting them. If I use the left rca plug, I get numbers like -29db, if I use the right I get -55bd or so. Any suggestions? Thanks!


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

Welcome to the Forum, Bob!

I assume the jack the meter has is mono, but you're using a stereo plug. Try a mono 3.5mm to RCA and see if that works.

Regards,
Wayne


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## rafa1552 (Jan 30, 2010)

Wayne A. Pflughaupt said:


> Welcome to the Forum, Bob!
> 
> I assume the jack the meter has is mono, but you're using a stereo plug. Try a mono 3.5mm to RCA and see if that works.
> 
> ...


I thought that could be the problem too. I'll pick one up. Thanks for the help.


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## Saddle (Feb 19, 2009)

Wayne A. Pflughaupt said:


> Welcome to the Forum, Bob!
> 
> I assume the jack the meter has is mono, but you're using a stereo plug. Try a mono 3.5mm to RCA and see if that works.
> 
> ...


I'm having the same problem. I was going to start a new thread, then found this one.

I'm not using a sub. Have the RS meter, and everything is working. My inputs and outputs are isolated (Right & Left) and the measurements do work. I don't have any kind of EQ processor in line. However, here is what I'm seeing:

I have calibration files loaded for the RS meter, and my sound card. I run the SPL check. Set the main out volume so my meter reads 75. Set the input level for -18db. I have selected 'use main speaker' for levels in both places. I have my meter set to 'C' weighting, and the box checked in REW.

Now... with all that set and working. When I open the measurement dialog box, and 'check levels', the sound output from the speakers at that point is greatly reduced. To my ears, it sounds like Pink noise, filtered for 'low pass' only. The high end is missing, and the levels are at that point some 20db down from where I set them for SPL calibration. Now, I can stop and return to the SPL check and it's right on. 

I can bump the input gain up at this point (or turn the amp up) and run a check and it works. But the true level readings on the graph are off by almost 20db. 

It sounds as if the Measurement 'Level Check' puts out pink noise filtered to test a sub woofer at this point. Could this be the problem? To my ears, the sound is quite noticeably different than the SPL calibration sound. I don't see anywhere in the settings to change the 'measurement level' signal frequency range, or device type.

My setup works, but there is a real difference in the measurement signal used for 'level check' and the SPL check. This difference is what appears to be the problem.

Thanks


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## glaufman (Nov 25, 2007)

It seems to me that the PN REW gives for in the MEASURE routine varies based on the settings you have entered for the endpoints of the sweep.


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

Welcome to the Forum, Saddle!


> It sounds as if the Measurement 'Level Check' puts out pink noise filtered to test a sub woofer at this point. Could this be the problem?


Yup, sure could. In the "Settings" window, “Sound Card” tab, down at the button where you Check Levels, change the window from “Use Subwoofer” to “Use Main Speakers.”

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

Saddle said:


> ...
> Now... with all that set and working. When I open the measurement dialog box, and 'check levels', the sound output from the speakers at that point is greatly reduced. To my ears, it sounds like Pink noise, filtered for 'low pass' only. The high end is missing, and the levels are at that point some 20db down from where I set them for SPL calibration. Now, I can stop and return to the SPL check and it's right on.
> ...


If you are talking about the Settings screen under the Soundcard tab, there is a choice to the left of the Check Levels button, where the default is "Use Subwoofer to Check/Set Levels". Here you would choose "Use Main Speaker to Check/Set Levels". 

In the Measured graph panel, when pressing the Calibrate button, I see a Choose signal source box that offers a default value of Use REW subwoofer cal signal. You want to choose "Use REW speaker cal signal". 

Either way, REW will now use band limited pink noise for the fronts, rather than the sub, for its calibration. 

Bill


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## Saddle (Feb 19, 2009)

Wayne A. Pflughaupt said:


> Welcome to the Forum, Saddle!
> Yup, sure could. In the "Settings" window, “Sound Card” tab, down at the button where you Check Levels, change the window from “Use Subwoofer” to “Use Main Speakers.”
> 
> Regards,
> Wayne


Thanks!!

I have that set in two places. Under 'Sound Card', Levels, it is set to 'Use Main Speaker to Check/Set levels.' And on the Mic/Meter tab, under Calibration, set to 'Use REW speaker cal signal.'

I made that mistake first. 

Thanks so much for your attention and help.


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## Saddle (Feb 19, 2009)

laser188139 said:


> If you are talking about the Settings screen under the Soundcard tab, there is a choice to the left of the Check Levels button, where the default is "Use Subwoofer to Check/Set Levels". Here you would choose "Use Main Speaker to Check/Set Levels".
> 
> In the Measured graph panel, when pressing the Calibrate button, I see a Choose signal source box that offers a default value of Use REW subwoofer cal signal. You want to choose "Use REW speaker cal signal".
> 
> ...


Thanks Bill! I do have those items set already. I missed those at first, but I've verified those settings several times.

I'm able to make a test as I mentioned, but the levels are off on the graphs. And there seems to be a different feed signal at that point, within the 'Measure' dialog box, than the signal used for SPL, and level checking within the sound card tab.

Thanks for your help and suggestions!
Saddle


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

You aren’t doing something like calibrating with one speaker running, then measuring with both, are you? I assume you did the “Calibrate SPL” routine after the “Calibrate Levels” routine?

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

Isn't that interesting. I had forgotten about the Check Levels button in the Measure dialog one uses to start a measurement. 

It appears there is a choice in the Settings Check Level routine, whether to use the subwoofer band limit pink noise or the main speaker band limited pink noise. When using the Calibrate button for the SPL meter above the graphs, again there is again a choice of which band limited pink noise to use. In the Measure dialog, though, there is no selection and to my ear it is using the Full range generator, not the sub cal or speaker cal band limited pink noise. 

How curious. I had never remarked the difference, but it is audible if one is paying attention. 

If you posted the graphs, it might help others verify exactly what you are doing. Are you perhaps using the Spectrum graph and doing RTA measures? Because of the way these measures and calculations are taken, they appear at a lower level than do sweeps. 

Bill


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## Saddle (Feb 19, 2009)

laser188139 said:


> Isn't that interesting. I had forgotten about the Check Levels button in the Measure dialog one uses to start a measurement.
> 
> It appears there is a choice in the Settings Check Level routine, whether to use the subwoofer band limit pink noise or the main speaker band limited pink noise. When using the Calibrate button for the SPL meter above the graphs, again there is again a choice of which band limited pink noise to use. In the Measure dialog, though, there is no selection and to my ear it is using the Full range generator, not the sub cal or speaker cal band limited pink noise.
> 
> ...


Well I think I figured it out. Not as if it were broken or anything.

After making sure of all of the above, I realized that when you click on 'Check Level' within the 'Measure' dialog box, the signal fed to the speakers is the bandwidth of pink noise that you specified 'IN THE MEASURE BOX'. So, if the measure range is 0-200, then you get that bandwidth of pink noise. If you change that to something like 20-5000, you get that range.

So in a small speaker system like the ones I mix with, there isn't a lot of volume on the low end, and most often the level check would tell me the signal was too low. I could still run the test of course.

So after changing the frequency range, the levels were where I expected, and where the software expected them. 

I wonder if... from a calibration standpoint for the software, if a broadband pink noise level there like the SPL would be best? But, at least I solved what 'seemed' to be a problem for me.

Thanks for all your help. This is a great forum, and great software!

Saddle


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## Saddle (Feb 19, 2009)

glaufman said:


> It seems to me that the PN REW gives for in the MEASURE routine varies based on the settings you have entered for the endpoints of the sweep.


I just read your comment, and that is what I found out as well. (read my post above) 

Once I realized that, and realized the level check signal was based on that range, it made sense. 

However, it may be a nice option so calibrate the SPL using the same range that you are going to sweep at.... Plots may be more accurate??

Thanks!


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## laser188139 (Sep 19, 2009)

Yes, Greg was right to start with. It happened, when I tried the Measure dialog Check levels, I had the range set at 10-20000, so it sounded like the full range measure. 

I think the point of Check levels in the Measure dialog is to verify that the input and output levels are adequate for REW to provide reasonable results. That may be why the button here is named Check levels, where the button on the SPL meter is labeled Calibrate. The Calibrate button gives the choice of band limited pink noise, appropriate to the speaker being used for the calibration. Generally, calibrating once per session makes sense. Then, the measures you take are comparable in relative levels; they don't change if you vary the measurement range being tested. 

Bill


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## embit (Jan 20, 2010)

I'm experiencing a similar problem to Saddle, and some of my issues might just be related to me being a complete noob to audio 

I'm using a 5.1 setup, so I'm measuring from 0hz to 22khz so I can get a big picture of what my room graph looks like. Right now I have nothing on the walls, so I'll be adding treatments after I can get at least a baseline graph in REW.

My problem: I can't get a graph of 0-22kHz with all of my speakers + sub. If I use my mains to set the levels, taking the measurements results in clipping with my sub on. If I use my sub to set the levels, taking measurements results in a very weird graph, most likely from too low of input levels.

"Use Main Speaker to Check/Set Levels" Settings:

WAVE Volume: 1.0
Output Volume: 0.5
Input Volume: 0.067
AVR's Volume: -8.0dB
The above settings get me a near perfect 75dB on my SPL meter, along with an input level of -19dB. When go into the Measure dialog, setup the range to be 0hz->22khz and hit check levels, the level ends up being too high (-9.2dB). If I take the measurement anyway, I get a clipping detected error. Most likely this is because my subwoofer is now generating sound, so the -8.0dB on my AVR is not the right value to use. So under settings I use the subwoofer levels to check/set levels.

"Use Subwoofer to Check/Set Levels"

WAVE Volume: 1.0
Output Volume: 0.5
Input Volume: 0.067
AVR's Volume: -37.0dB
This also gets me a 75dB reading on my SPL meter and the input level is still around -19dB, but what shocked me was the volume necessary on my AVR. Why so low!? could this be signifying a problem elsewhere? Anyway, if after setting these values I go into the measure dialog and hit "check levels" with the 0hz-22khz range, the dialog tells me the level is too low (-26dB). If I take the measurement anyway, I don't get any error dialogs, but the graph looks very wrong. At around 20hz it starts up near 90dB, and steadily falls until it's around ~35dB up in the 15khz range... that can't be right, can it?

So, thoughts? Is my problem because I'm trying to measure both the sub and the mains at the same time, and REW just isn't setup to work like that? Should I instead do one graph 0hz->200hz, for the sub, then another graph 0hz->22khz with the sub turned off, just for the mains?
:huh:


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## laser188139 (Sep 19, 2009)

Andy, one obvious hypothesis is that you have the level of your sub set much higher than your mains, and that the graph you are seeing is correct. But there are other possibilities that could explain bizarre measurement results. 

If you go to the Filter graph, with your full range measure, you can also enable Mic/Meter calibration and the Soundcard Cal. Use the Graph -> Save graph as JPEG option to generate a picture, save it, and upload it. Looking at the picture, it might be obvious that there is something weird about the soundcard or mic calibration that is biasing the measurements to appear as they are. 

Bill


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## embit (Jan 20, 2010)

Thanks Bill, I checked some things out, and you were right about the sub being run higher. Somehow the gain nob on the back of the sub was past where I had originally set it. Must have fat fingered it or something...

anyway, I reset it, and re-ran through the audyssey calibration procedure on the AVR. I then made sure that each and every speaker measured 75dB at my listening position.

Re-measured using REW, and fixing the gain/recalibrating helped, but I'm still confused. Using the speaker levels my AVR's volume was set at -14dB, and sub levels was set at -28dB. Does this make sense? I would have thought that since everything is calibrated to be 75dB, there wouldn't need to be a volume change at all...

running the measurements didn't result in any errors this time, but I still think the graphs look weird. For starters, they don't even match!

Main speakers to set/check level graph:








Sub to set/check level graph:








thanks!


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## laser188139 (Sep 19, 2009)

I'll share with you an experience I described in another thread earlier today:

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 appears that 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.

In addition to the problem of interference between two mains affecting the level viz-a-viz the sub's level, the second graph appears to me that it has more smoothing than the first. One of the peculiarities of REW if you have multiple measures, is that if you close one and the others slide up, trace adjustments such as smoothing and trace offset stay with the slot, they don't move when the measures move up to take the place of the closed one. So you can end up with cases where you inadvertently have more smoothing on one measure than another. To my eye, the two curves have the same shape, it's just that the first one is rougher. 

Try taking a measure of the sub with just one front channel driven at a time. The resulting curves will show you better whether the sub's level is even with each channel individually. (It took weeks before this occurred to me. Wayne just advises people up front to measure one main at a time, which avoids the painful learning experience of why this matters.)

Bill


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## embit (Jan 20, 2010)

ahh, that makes sense. Calibration for each speaker was done individually, but when I'm running REW I'm driving all 5 speakers + sub. So really if I want accurate REW graphs based on a 75dB calibration, I'll need to generate graphs for each speaker separately? that makes sense, I guess I just wasn't expecting to have to do this 6 times...


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

embit said:


> I'm using a 5.1 setup, so I'm measuring from 0hz to 22khz so I can get a big picture of what my room graph looks like. Right now I have nothing on the walls, so I'll be adding treatments after I can get at least a baseline graph in REW.


What are you using to measure? For full range measurements, you need a calibrated mic. That you’re having clipping issues tells me you’re probably using an SPL meter instead?




embit said:


> Re-measured using REW, and fixing the gain/recalibrating helped, but I'm still confused. Using the speaker levels my AVR's volume was set at -14dB, and sub levels was set at -28dB. Does this make sense? I would have thought that since everything is calibrated to be 75dB, there wouldn't need to be a volume change at all...


This graph should help explain the problem you’re having. It’s an in-room RTA snapshot of the test tones from a Denon receiver. REW’s test tones are similar, narrow band signals.










So, you can look at your own graph and see why you had to turn the AVR’s volume down so low when you used the Subwoofer test tone. Your 40-50 Hz region is 15 dB hotter than the 1 kHz region in the top graph, and nearly 30 dB in the lower.

So, even though you turned it down, your sub is still quite a bit hotter than your main speakers.

Regards,
Wayne


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## embit (Jan 20, 2010)

Wayne A. Pflughaupt said:


> What are you using to measure? For full range measurements, you need a calibrated mic. That you’re having clipping issues tells me you’re probably using an SPL meter instead?
> 
> 
> This graph should help explain the problem you’re having. It’s an in-room RTA snapshot of the test tones from a Denon receiver. REW’s test tones are similar, narrow band signals.
> ...


Thanks for your reply Wayne, to answer your first question, yes, I'm using a radio shack SPL. My ignorance is showing, but why does one work for full range, and the other doesn't?

as for the graph you posted, that does make sense for what I'm seeing. Is that graph basically a result of these AVR's EQing my speakers? does this mean I should try to disable any internal EQs on my receiver to get a "pure" measurement, or do I actually want to include the EQs as part of my measurements?

So I guess my next question is this: what is the proper way to use REW to get a "big picture"? from looking at the other threads it looks like most people just test the subwoofer, 0-200hz. Should I just do 0-22kHz for each speaker (including sub) individually?


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

> why does one work for full range, and the other doesn't?





> So I guess my next question is this: what is the proper way to use REW to get a "big picture"? from looking at the other threads it looks like most people just test the subwoofer, 0-200hz. Should I just do 0-22kHz for each speaker (including sub) individually?


Our testing of numerous Radio Shack SPL meters prior to launching this Forum, both current-model and vintage, showed that they were fairly consistent up to about 3 kHz. Above that point they were all over the map, which made it impossible to generate a calibration file that would be accurate above that point. If you want full range measurements, it’s best to get a ECM8000 mic w/ pre-amp. We provide a generic calibration file for the mic, but they do vary somewhat in response from one to the next. If you’re concerned with the best accuracy, it’s best to spring for a mic with custom calibration.



> Is that graph basically a result of these AVR's EQing my speakers? does this mean I should try to disable any internal EQs on my receiver to get a "pure" measurement, or do I actually want to include the EQs as part of my measurements?


That graph has nothing to do with equalization. It’s just what receivers and REW generates for level setting, in the latter’s case, prior to taking the actual frequency response measurement.

Take the full-rage test tone (green/red). You can see the tone is “haystacked” at about 1000 Hz. That's the same thing that the measurement mic (i.e. the SPL meter, if that’s what you’re using) is “seeing” when REW generates its “Set Levels” signal. But what if your speakers have high output at say, 300 Hz? Well, that’s not going to show up when the response-limited level-setting tone is generated. But when REW generates the _full range_ tone for the measurement, it will. Your high 300 Hz output is going to show up on the graph. 

So - this is why you often see measurements (both sub and full range) significantly above the 75 dB Target.

Regards,
Wayne


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