# Using Room EQ Wizard Without a Mic/Meter



## MikeRivers (Feb 13, 2007)

I'd like to use REW Wizard to plot the frequency response of a piece of hardware, and equalizer, for example. I'm simply connecting the device between the line out and line in of my audio interface, setting levels, and making a measurement. It works fine, but every time I start, it bugs me about not having a calibration file. I tell it go go ahead anyway.

Can I create a file to feed it that represents a meter (unweighted) with flat response? Is it as simple as connecting input to output directly, making a measurement, and saving that as a calibration file? Do I need to tell it that it's not weighted? 

Or do I need to create a comma separated text file with some data points?

While I'm at it, is there a way to store an offset? When making a measurement, it comes out centered around 65 dB. I want to end up with a graph, typically to use in an article, that shows the response referenced to 0 dB. I can enter an offset for each measurement and that gets me what I want, but is there a place to enter a default offset?


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

Hey Mike,

Taking a measurement of an electronic device like an equalizer is the same process as creating a sound card calibration file, which is adequately described in the Help Files and the on-screen prompts in the program. There is no “weighting” involved in a sound card calibration, so you shouldn’t be getting a request for a mic calibration file. If it’s a sound card calibration file it’s asking for, just generate one for your interface and load it, and that should be the end of that.




> While I'm at it, is there a way to store an offset? When making a measurement, it comes out centered around 65 dB. I want to end up with a graph, typically to use in an article, that shows the response referenced to 0 dB. I can enter an offset for each measurement and that gets me what I want, but is there a place to enter a default offset?


As long as the equalizer does not have any filtering engaged, it will generate a graph at 0 dB. If filtering is engaged, the graph may move from 0 dB. Again, generating these graphs is the same thing as generating a calibration file, and as far as I know there is no offset feature available for sound card measurements, as there is with regular room measurements. John M can clarify if I’m mistaken about this.

P.S. Welcome to the Forum!
Regards, 
Wayne


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## JohnM (Apr 11, 2006)

REW won't be asking for a cal file, just to calibrate the SPL reading. You can solve both problems by connecting a loopback, playing a signal at the level you usually measure at, opening the SPL meter, clicking Calibrate, and telling REW the level it is seeing is 0 dB. Your subsequent measurements will then be relative to the level you used for that level calibration step. 

If you want to also calibrate out the roll-off of your audio interface, leave the loopback in place and follow the steps for calibrating the soundcard.


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## MikeRivers (Feb 13, 2007)

JohnM said:


> REW won't be asking for a cal file, just to calibrate the SPL reading. You can solve both problems by connecting a loopback, playing a signal at the level you usually measure at, opening the SPL meter, clicking Calibrate, and telling REW the level it is seeing is 0 dB. Your subsequent measurements will then be relative to the level you used for that level calibration step.


Thanks. I thought that might be the step I was missing, however, if you're talking about the dialog box in the SPL Calibration window that says "SPL Reading Calibration" it won't let me set that to 0. It'll only go down to 55 dB. When I enter 0, it just ignores my entry and returns to whatever it thinks, which in my case is about 76 dB. 

I can get the graph centered around 0 dB by entering an offset in the window that comes up when clicking the Controls button but I have to do that for every measurement.


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## JohnM (Apr 11, 2006)

MikeRivers said:


> if you're talking about the dialog box in the SPL Calibration window that says "SPL Reading Calibration" it won't let me set that to 0. It'll only go down to 55 dB.


You must be using V5.0, switch to the beta version.


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## MikeRivers (Feb 13, 2007)

JohnM said:


> You must be using V5.0, switch to the beta version.


When I'm just learning my way around a program, I tend to avoid beta versions, but I guess after a few days of playing around, I'm an expert, so I'll give it a go. 

Thanks.


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