The Mic/Meter Preferences allow selection of the Mic/Meter type, loading/clearing of a mic/meter calibration file to use for new measurements and calibrating the REW SPL meter's SPL reading.
Select the C Weighted SPL Meter check box if you are using a C weighted SPL meter as the input to REW, subsequent measurements will then be corrected to remove the low and high frequency roll-offs of the C weighting characteristic. If a cal file is loaded the correction will only be applied outside the frequency range covered by the cal file.
If you have a calibration data file for your SPL meter or microphone you can load the data into REW by clicking the Browse button. The calibration data will be applied to all new measurements taken after it has been loaded and will be shown on the SPL and Phase graph for the measurements. To remove the calibration data file click the Clear Cal button.
To apply or remove a calibration file for an existing measurement, use the Change Cal... button in the measurement panel.
The calibration file is a plain text file which by default has the extension .cal, though other extensions are also accepted. It should contain the actual gain (and optionally phase) response of the meter or microphone at the frequencies given, these will then be subtracted from subsequent measurements. The values in the calibration file can be separated by spaces, tabs or commas. Typically the values are relative to the level at some reference frequency, e.g. 1kHz, so the gain value there is 0.0.
SPL Meter Calibration data 20 -15.38 50 -3.69 100 -1.34 200 -0.62 500 -0.26 1000 0.0 2000 1.80 5000 3.95 10000 -0.71 20000 -6.28