2.6. Tuning Curves Fitting and Q10dB

Each PTC was fitted with two quadratic functions, one on the low-side and one on the high-side around the probe frequency (R²: Mean = 0.980; SD = 0.037; min = 0.778; max = 1.00). Slopes on both sides were considered monotonic, so if a masked threshold did not follow this rule with a deviation higher than 10 dB, it was not taken into account for the regression. Following this rule, the typical fitted-function included all the seven masking thresholds except for three subjects: subject S04 (6 points for the “Low” spread curve and 5 points for the “Medium” curve), S07 (6 points, “Medium” spread) and S19 (6 points, “Low” spread). Moreover, S16 did not manage to perform the test and the PTCs could not be established so, the results were analyzed for 19 subjects (out of 20). From the fitted PTCs, we then characterized channel interaction using the Q10dB as a sharpness factor. Q10dB was calculated by dividing the probe frequency by the PTC bandwidth (BW) at 10 dB above the tip level (Q10dB = 2226/BW10dB).