## Calibrating the SPL Reading

Calibrating the SPL reading gives REW an absolute SPL reference by entering a reading from your SPL meter while a speaker or subwoofer calibration signal is playing. Alternatively an SPL calibrator may be used.

### SPL Calibration Procedure

1. Select the Mic/Meter tab of the Preferences panel
2. If using an SPL meter set it to C weighting and select the C Weighted SPL Meter box in the Mic/Meter Preferences. Set the meter range to suit the measurement level used in the check levels process (the 80dB range is recommended for the Radio Shack meter). If using a USB mic or a mic and preamp select the Mic or Z Weighted SPL Meter option.
3. Open the REW SPL meter by clicking the SPL Meter button in the toolbar then press the Calibrate button
4. On the dialog which appears choose whether to calibrate the meter reading using your subwoofer or a main speaker driven by a calibration signal generated within REW, or to use an external test signal you provide, making the appropriate selection in the drop-down box and clicking OK.
5. Enter the reading from your external SPL meter (not the REW meter) in the calibration panel and press Finished when done

For more information about the REW SPL Meter see the SPL Meter help

### SPL Calibration Notes

- If you are using a USB mic with a cal file that contains a sensitivity figure SPL calibration is not required, REW will show this message:.
- At the end of the calibration process a message is displayed showing the maximum SPL that can be measured with the current input level settings. If higher SPL needs to be measured the input sensitivity must be reduced (by lowering the soundcard input volume setting or, if using an external microphone preamp, reducing the preamp gain or, if using an external SPL meter, increasing the range setting) and repeating the calibration
- A warning is shown if measurements are attempted before calibrating the SPL reading as the results of the measurement would not reflect the actual SPL. The SPL reading is shown in red until the SPL calibration procedure has been completed
- REW remembers the calibration setting for the next startup, so it will usually not be necessary to repeat this process, but check the REW SPL reading against your SPL meter or calibrator before starting a new set of measurements
- If the input volume setting is changed or another soundcard input is selected it will be necessary to repeat the calibration process (selecting a different input or input device will cause REW to treat the SPL reading as uncalibrated - the reading goes red)
- if the signal generator is already playing a signal when you click Calibrate it will continue to play the same signal

REW is now ready to make measurements.

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