# How to calibrate Mic/USB preamps/computer



## BRUCEMX (Mar 9, 2013)

Hello all.
I am running Windows 7 on Parallels 8 on my MacBook Pro. I am finding it difficult to know where to start the volume/level adjustment setting process. 

With effectively 2 laptops in one with 2 volume adjustments for each one(That makes 4 possible settings) and then input/output on the M-Audio pre (That's 2 more) and then one more in the case of using alternate RTA software (adds 1 more point of volume adjustment). So that's 7 points of volume adjustment that I need to sort out and set up before I can get to an exact and true SPL measurement. Don't I just have to use a reliable freshly calibrated unit and match that and be aware during testing that say one volume for Windows and one volume for mac need to be set at a preset value prior to testing. 

In car audio testing we simply used the Audio Control unit and considered the SPL measurements to be all relative so exact calibration was done every 6 mo. I want more control than that. Any help would be helpful and appreciated. 

Thank you;
Take care;

John Eldred


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## JohnM (Apr 11, 2006)

SPL readings are only affected by the input volume control(s), once you calibrate REW's SPL meter (by reference to an external SPL meter) it will stay calibrated as long as you don't alter volume controls in the input path.


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## BRUCEMX (Mar 9, 2013)

Thank you for your note. I was a little confused due to my having to run some 1/8" loops to test equipment as well as performing standard RTA testing projects.
Thanks Again.

John


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