Artificial-mouth pressure p_mouth, mouthpiece pressure p_mouthpiece and external sound pressure p_extern when recording a mouth-pressure ascending ramp at 1 kPa/s. On the right side, zoomed view of 300 ms around the tone onset. R indicates the threshold of oscillation, considered to assess resistance (vertical red line indicates the first instant where p_mouthpiece > 0.5 kPa). B indicates the time interval of mouthpiece pressure used to compute the spectral centroid (Fig. 7), considered to assess brightness. L indicates the external sound amplitude considered to assess loudness, at p_mouth between 12 and 12.5 kPa. [Mouthpiece no. 10, first repetition].