The L1–L2 acoustic measure as a reliable quantification of the second passaggio transition of professional sopranos

Professional classical sopranos exhibit a perceivable acoustic transition called the second passaggio when singing [ɑ] between the musical notes D♮5 (587 Hz) and F♮5 (698 Hz). The transition involves an adjustment from second resonance tracking of the second harmonic (f R2/2f o) to first resonance tracking of the fundamental (f R1/f o). The transition was quantified as the difference between the radiated sound levels of the first and second harmonics (L1–L2) and was expected to appear as a change from negative to positive values of L1–L2 in ascending chromatic scales between C♮5 and G♮5. The experiment included 17 sopranos: nine were judged by the first author to make the change consistently, while eight were judged as inconsistent or incapable of executing the transition. Acoustic results showed that the sopranos who achieved L1–L2 values greater than 15 dB SPL at G♮5 exhibited three important traits that were not observed in the singers who achieved low positive or negative values of L1–L2 at G♮5: a transition from negative to positive L1–L2 values consistently early in the chromatic scale, minimal variability within a musical note, and a steep rate of change in L1–L2 over the course of the scale.