# Calibration of REW's internal SPL meter.



## gapmedia (Jan 24, 2014)

Hi,

I am new to REW and the forum. Please excuse my newbie question.

I have a Behringer UCA202, XENYX802, and ECM8000 mic. I realise that as I am using Windows XP I will have no input level control for the UCA202 within XP. I can calibrate the soundcard successfully, but I am having trouble understanding REW's SPL Meter calibration procedure.

I also have a sound level calibrator that outputs the standard 1khz signal at 94dB or 114dB. I thought to calibrate REW's internal SPL meter to the UCA202 and ECM8000, I would feed a 94dB signal into the mic, and match the readout on REW's SPL meter to 94dB by adjusting the XENYX802's levels. I cannot achieve this sound level on REW's SPL meter. I can only get to around 84-86dB for memory before I am overloading the XENYX802. Is this where input level control within XP would come in 'handy' for the UCA202 in helping me achieve a higher level to REW's SPL meter?

Is what I am trying to do/achieve in anyway correct? Do I need a separate/external SPL meter to correctly calibrate REW's internal SPL meter to say 75dB? Is the 'external signal' option mentioned in REW's SPL meter calibration window referring to a different type of 'external signal' than one (94dB) from a sound level calibrator?

What could I expect to be the highest dB level REW's SPL meter can handle when setup correctly?

Thanks for your help, and apologies for the questions.

Simon


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

Hi Simon,

Sine waves are not the best signal source for the SPL calibration test, which is why REW generates a broadband pink noise signal for this process. If you don’t have a SPL meter you can run the SPL calibration anyway. Just start the test signal, adjust your system’s volume to a comfortable level and click “Finished.” REW will then “think” that level is 75 dB and you’ll be able to produce usable measurements.

Regards, 
Wayne


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## gapmedia (Jan 24, 2014)

Hi Wayne,

Thank you very much for the advice. I think it is probably wise to invest in an SPL meter after all.

Regards,
Simon


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

That’s really only necessary if you require absolute SPL calibration of your frequency response graphs for some reason. Even without calibrating against a meter, any response deviations the graphs show will accurate (for instance if there is a 12 dB span between a peak and adjacent trough) even if the absolute dB values indicated aren’t (i.e. a bass peak might show as 77 dB when it’s really only 74 dB). IOW, even without calibrating against a meter you can still get perfectly acceptable and usable and graphs. Make sense? 

Regards, 
Wayne


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## Lumen (May 17, 2014)

Wayne A. Pflughaupt said:


> ...REW generates a broadband pink noise signal for this process. If you don’t have a SPL meter you can run the SPL calibration anyway. Just start the test signal, adjust your system’s volume to a comfortable level and click “Finished.” REW will then “think” that level is 75 dB and you’ll be able to produce usable measurements.


Just asking--I'm new to REW as well. Did you mean to say "comfortably loud level?" I ask because I think it would be easy for serious nulls to swamp a "comfortable level" if it weren't loud enough. Isn't that why reference levels are preferred to begin with? 

It's common to see 30dB dips in rooms, many of which have noisy background levels approaching 50dB or so. A subjective "comfortable level" of 60dB in this scenario would provide only 10dB headroom and swamp out serious nulls, at least for frequency response plots, correct?

In any case, your suggestion sounds like a useful tool for measuring hobbyist's bag-of-tricks. Thanks!


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## gapmedia (Jan 24, 2014)

Thanks Wayne, that does make sense. However, I am hoping to use REW more for loudspeaker response measurements and less for room equalisation at the moment. I am building small 'fullrange' speakers, and would like to use REW to measure their frequency response and absolute SPL at 1W/1M.

Regards,
Simon


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