Calibration

The goal of calibrating the setup is to achieve an agreement between physical values and internal values of sound pressure level (SPL). In other words, if the current sound pressure is, e.g., 70 dB SPL, the internal measure of the sound pressure should be 70 dB SPL as well; and for the output vice versa.

In openMHA this is achieved by setting the values of mha.calib_in.peaklevel and mha.calib_out.peaklevel. You can read out the current internal levels with the Octave-based openMHA GUI using the "levels" tool. There, it can help to select the 2 second averaging.

There are several ways of calibrating the device:

Ad-hoc "calibration" without level meter

Configure the hearing aid prototype with the "nogain" fitting (using the openMHA GUI).

Ask someone to talk normally and continously in a quiet environment and read out the internal levels at a distance of 1 meter. To "calibrate" the input, configure mha.calib_in.peaklevel such that the internal value is about 65 dB in that situation.

Then, find a noisy environment with a constant level, e.g., switch on a hair dryer, microwave oven, or vacuum cleaner. To calibrate the output, configure mha.calib_in.peaklevel such that the perceived loudness is similar when hearing with the hearing aid prototype and without it.

Calibration with a level meter

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Calibration with professional equipment

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