The interplay between glottis and vocal tract during the male passaggio.

The transition between 'chest' and 'head' register is essential for male opera singers in order to reach the higher pitches. The 'passaggio', which is a scale passage where this transition takes place, but also a maneuver of register equalization, is typically difficult to learn. Studies on parameters for a definition of this transition are restricted to a small number of singers so far. Audio, electroglottographic, and equivalent subglottic pressure signals of 11 male opera singers were recorded while singing scales on open back vowels and passing the register transition. A spectrum analysis of the audio signal revealed that the second harmonic (H2) dominates in 'chest', resonated by the first formant (F1), together with the fourth harmonic (H4), supported by the second formant (F2). During the passaggio, H2 level decreases because it loses the resonance of F1, while the third harmonic (H3) gains the resonance of F2. At this point the H4 level drops because that harmonic is no longer supported by F2. The transition from 'chest' to 'head' register is marked by characteristic changes in the amplitude patterns of the partials H2, H3, and H4, and the frequency progressions of the first two formants, defining an objective distinction between the two registers.