## Mic/Meter Preferences

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.

#### Type

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.

#### Mic/Meter Calibration

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.

#### Calibration File Format

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.

- Each line of calibration data must have a frequency value and a gain value, a phase value is optional
- Frequency is in Hz, gain in dB, phase in degrees
- The cal points can be at arbitrary frequency spacing, but each line must have a higher frequency than the one before and there must be at least 2 freq, gain data pairs
- Only lines which begin with a number are loaded, others are ignored
- In comma-delimited files there must be at least one space after the comma
- Spaces before values are ignored

Here is an example section of a valid file format:

    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

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