umik-1 calibration file

Hi, I have loaded my Mic Cal file for the UMIK-1 in the preferences and created a soundcard calfile. Both show up in the CALfile Tab of the Preferences-window. Next I Open the SPL meter to calibrate the level and as soon as I hit 'Calibrate' REW asks if I have a Cal file for the UMIK-1 'Yes'...

Dear experts, At first: Thanks a lot for this marvelous software! I need to measure some microfones using REW for which it is necessary to have a linear response of a loudspeaker. The normal way is to use a good linear loudspeaker and measure it´s frequency response using a calibrated mic...