Amplitude Calibration procedure example

The desired amplitude level must be entered in the Input Level field of the Settings/Calibration window.

Next, the Calibrate INTERNAL source level or Calibrate EXTERNAL source level button must be pressed.

If the Calibrate EXTERNAL source level is pressed, an external pure tone generator (microphone calibrator or other similar device) is supposed to be used.

If the Calibrate INTERNAL source level is pressed, the soundcard must be connected in loopback (input connected to output).

Before starting the procedure, be sure that the input level (and output level in case of internal calibration) of the soundcard are correctly set. Check this with some test measurements, in the Scope window.

After this procedure, the amplitude values have been calibrated.

In this example an SPL (dB) calibration procedure with a pure tone of 94 dB is shown. The same can be done with other types of calibration (Volts or mVolts).

IMPORTANT NOTE: the Transfer Function Measurement option in the Settings/FFT window must be disabled in order to show amplitude values of data according with the above calibration settings.

Also, FFT length and buffer length must be the same and all scope data must be selected, in order to have the better accuracy of the FFT peak amplitude value, according with FFT and Signal Processing theory.
This is done automatically when data are measured and analyzed in the RTA window.

CALIBRATION VERIFICATION:

To check the correct calibration, for example in case of internal calibration, a 1 kHz signal can be set as internal signal source in the Settings/General window.

Now a measurement can be performed. Open the Scope window, select all data and open the FFT of scope Data window.
In the below picture the Rectangular data weighting window is used.

The amplitude of the 1 kHz tone peak will be now 94 dB.

The calibration can be verified also in the RTA window.

Narrow band spectrum:

1/3 Octave bands: