On the Calibration menu item, users have the opportunity to calibrate their smartphone.
The smartphone calibration is a crucial and recommanded step. Without calibration, you can be sure that the measured data will be wrong!
The methodology is based on the knowledge of a Reference value for the equivalent noise level Leq (in dB, not in dB(A)) for a given duration, from a reference device (an acoustic calibrator, a calibrated smartphone, a sound level meter). Depending on the calibration method, the calibration can be performed for a given frequency band or for the full range (global value). This Reference value is then compared to the Measured Leq (in dB) using the smartphone. The difference between these two values gives a correction factor (i.e. the signal gain) that will be applied to the input signal.
Several calibration methods are possible:
This calibration protocol is based on the low variability of the average noise emission of individual vehicles. The advantage of this protocol for the user is that it does not require specific equipment, i.e. reference sound source or device, or special knowledge in acoustics. The method consists in measuring the noise level of a few vehicles as they pass through at different measuring points. The measured levels are compared to the levels expected by a numerical model, the difference serving as an offset for subsequent measurements. The robustness of the protocol was tested in real conditions with a set of 8 smartphones. The comparison with a class 1 sound level meter on 6 control points shows an average error on all phones of −0.6 ± 1.2 dB(A).
This innovative method is described in the following article: Aumond, P., Can, A., Gozalo, G. R., Fortin, N., & Suárez, E. "Method for in situ acoustic calibration of smartphone-based sound measurement applications". Applied Acoustics, 166, 2020.
When using a 'Global' value for the calibration, make sure that the Reference value will be obtained using the same frequency range that your smartphone.
The 'Calibration warm-up time' and the 'Calibration duration' can be modified in the Settings.
During calibration, the smartphone and the reference device must be used in a similar way.
In this method, a smartphone already calibrated with NoiseCapture, can calibrate one or more smartphones. On the side of the microphones to be calibrated, the procedure is fully automatic. The entire system is controlled by the reference smartphone.
Selection of the Transmitter (1) or Receiver (2) mode
Selection of the Pink (1) or Ambient (2) noise source