Combined input calibration example: Calibrating to measure absolute SPL

Go to Measurement->Calibration..., in the dialog and click the  button shown below.



Make sure Use input calibration is checked.

You should now see the dialog shown below.



Note: A faster method of displaying this dialog is to click the  button on the Standard toolbar.


In step number 1a, make sure  is checked and select  in step number 1b. as shown above.

In step number 2, we have selected . If you select , you first need to calibrate your sound card before calibrating your microphone (or another transducer). The  calibration must be used if you do not have a calibrator but the sensitivity of your microphone is known (e.g. 20 mV/Pa). Use also  if you have an external input amplifier with fixed gain steps and want to adjust the gain steps of this amplifier, or if you are using WinMLS to perform both electrical measurements and measurements using a microphone.


If you want a quick and simple calibration, we recommend that you use  as selected above.


Note that the number  shown in the figure above is updated after the calibration. It shows the maximum input level that WinMLS is able to measure (a higher level will result in digital clipping). In this case it is 130.654 dB SPL. If you want to measure SPL higher than 130.654 dB, e.g. 140 dB, you have two alternatives:

      If WinMLS is set to control the sound card mixer, and the input volume is not set to minimum during the calibration, you can measure higher input levels just by decreasing the sound card mixer input volume slider.

      If WinMLS is not set to control the sound card mixer, you must decrease the sensitivity on either the sound card, pre-amplifier or microphone and redo the calibration.


In step number 3, click the  button to start the calibration.


The dialog shown below will be displayed (it may look somewhat different dependent on the selected type of calibration).



Type in or choose the correct settings for your calibrator. In the figure above 1000 Hz and 94 dB is selected. You will find the output level of your acoustic calibrator in the calibrator documentation (usually it is also written on the calibrator).


Connect the calibrator to your microphone.

Click the  button (shown in figure above).

Turn on the calibrator to see if the input level is acceptable.

The WinMLS mixer dialog will pop up to give you the levels, if not, you can also find the levels on the status bar found at the very bottom of the WinMLS program . The level should be in the range -30 dBFS to -1 dBFS. If the level is less than 30 dBFS, it should be increased (a warning will be given if this is the case when you perform the calibration).

Click the  button to perform the calibration. This will exit the dialog box if the calibration is successful. It takes a few seconds and afterwards the new conversion factor and date and time for the calibration is displayed as shown below.



Now click the  button to exit the calibration screen.


This completes the calibration of input channel 1. Note that if you are doing a 2-channel measurement and also want calibrated values for channel 2, you need to calibrate channel 2 as well.


Verify that the calibration is correct