A Thing or Two about Passaggio

14 Feb A Thing or Two about Passaggio

Vocal passaggio discussion is often filled with controversy. Much of the ambiguities originate from failing to distinguish clearly between the laryngeal and acoustic events surrounding it.

The vocal passaggio, because of its pedagogical importance, especially in male voice training, and the ambiguities surrounding it, merits some clarification. The deeper knowledge of it that we now possess, largely came from the advances in the science of vocal acoustics.

Primo (Lower) Passaggio

Traditionally, the primo (lower) passaggio was understood to be the pitch at which a singer, singing an ascending scale, has to switch from M1 (or “chest” or “TA dominant”) voice to M2 (or “head”, or “CT dominant”) voice, unless he/she had already started to gradually do so earlier in the scale. The primo passaggio as such basically applies to untrained singers, because the trained ones learn how to smoothly negotiate the transition; they sing the entire scale with a mix of M1 (chest) and M2 (head) voices, the M2 gradually prevailing as the pitch ascends. For that reason, the importance of the primo passaggio concept is questioned today, and some written sources discuss only one passaggio in males – the secondo (upper) passaggio, but agree with the two passaggi in females. It is quite logical to agree with the notion, as primo passaggio has no real significance for trained male singers other than to indicate where approximately the “zona di passaggio” commences. Whatever the case, the location of the primo passaggio is quite stable for each voice and more-or-less independent of the vowel sung.

Secondo (Upper) Passaggio

For men, the secondo passaggio is located about five semitones above the primo passaggio. At this point the singer is expected to give up any of the residual M1 (chest) voice, bringing the vocal folds into a fully stretched position of the M2 (head) voice. Needless to say that singing above the secondo passaggio, with the vocal folds already fully stretched, requires assistance from larynx’ external musculature, the use of which is still not fully understood, especially in tenors whose repertoire requires that they climb another 6-7 semitones above their secondo passaggios. The choices of muscles and mechanisms to use for the task are multiple, and it is highly likely that through the influence of their teachers, or by accident, different singers arrive at different solutions for singing the “high C”. Even the elite ones differ greatly in their approaches. Power spectra analysis of the voices of Luciano Pavarotti and Placido Domingo singing the final B4-flat of “Celeste Aida” on word “sol” in “un trono vicino al sol” shows two completely different vocal strategies as demonstrated by Donald Miller and his collaborators at the Groningen Voice Research Lab.

For female voices, the existence of two passaggi is generally agreed upon, the upper passaggio sitting about an octave above the primo passaggio.  

The short zone between the two passaggi in male voices is called the zona di passaggio, the mastering of which takes much of male’s vocal training. The challenge and the difficulty of passaggio training lies in the fact that in addition to the laryngeal events of the lower and the upper passaggios described above, it happens that certain acoustic events take place just around the male’s short zona di passaggio as well.

The Acoustic Events Surrounding the Passaggi. Harmonics and Formants

The acoustic events result from the interplay between the harmonics (H1-the fundamental, H2-an octave higher, H3-a 5^th higher, …) of the note sung, and the natural resonant frequencies of the vocal tract, the so-called formants. There are several formants of the vocal tract, but the first two (F1, F2) are the most important, as they correspond to the two main resonators of the vocal tract – the pharynx and the oral cavity. The pitches of the formants change as we shape the vocal tract or the vowels sung by changing the position of the articulators (lips, jaw, tongue …).

The resonant voice and the chiaroscuro effect of the operatic singing are produced by continuously and opportunistically matching the pitches of certain (well chosen) formants of the vocal tract with certain (well chosen) harmonics of the note sung, so that they co-resonate and amplify the sound, uniformly throughout a scale. Mastering the skill of matching the two is an important subject of vocal pedagogy.

What happens just around or inside of a man’s zona di passaggio is that some critical movements of the harmonics relative to formants take place: as the singer ascends the scale on the same vowel, one or more harmonics move and pass above the 1^st formant, after which they cannot help co-resonate the formant anymore, and the voice loses its resonance, until another formant/harmonic match is established. The pitch of a formant is vowel-dependent, therefore the locations of the acoustic event will change as we sing words consisting of different vowels.

Therefore, to produce a good resonance while going through the zona di passaggio, the (male) singer needs to negotiate several things at the same time: chest-to-head voice balance, vocal tract shaping for optimum harmonics/formants matching and some vowel modification so that the match is facilitated.

A pivotal point in the zona di passaggio is when the 2^nd harmonic passes the 1^st formant, thus “turning” the voice. In some schools of singing this is called “covering”. In classical singing the singer needs to learn how to allow the turn to happen, as his untrained instinct is not to. The turning is not produced by laryngeal adjustments or by switching from M1 (chest) to M2 (head) voices; it is a result of an acoustic event. But to complicate things further, vocal research also shows that if a singer does produce a good resonance, that quality can feed back to the larynx and support its muscle function, and vice versa. 

 “Laryngeal registration adjustments are sometimes independent of acoustic registration events but are also often influenced by interactivity with acoustic registration phenomena. Any shortcoming in one will adversely affect the other.” (Kenneth Bozeman). That is why singing well in the passaggio is hard, while Giuseppe Verdi anecdotally asserted that the male voice sounded most beautifully just there, and composed his arias accordingly!

Adding still to the complexity, the zona di passaggio for a male voice extends well into the top of the singer’s range, so the challenge of singing high notes adds another level of difficulty to passaggio training. 

Much of the passaggio narrative focuses on male voices. The female voices, singing an octave higher than the males, are in a very different position. Their lower passaggio is a real event. It sits in the lower range of the voice, not giving ladies much space for starting the transition to M2 (head voice) much earlier in the scale. Female voices have fewer options for matching harmonics and formants – singing an octave higher than a tenor, all soprano’s harmonics except the 1^st (H1, the fundamental pitch) sit above the 1^st formant (F1) for most of the time. 

The secondo passaggio of a female voice seems to be an acoustic event, the point where the 1^st harmonic (finally) reaches the 1^st formant, re-establishing a good resonance that was lacking in the long middle voice resonance void. Henceforth the ladies’ primary concern is how to continue tracking the 1^st harmonic with the 1^st formant as the pitch rises. The resonance void in the middle voice is caused by the shortage of suitable formant/harmonic matches: H2 has surpassed F1 somewhere around the primo passaggio, while H1 is about an octave lower than F1 at that point. If there were such a thing as passaggio training of female voices, it would be the management of the acoustic void in the long interval between the bottom and the top of the treble clef.

The males, conversely, have a lot of harmonic “material” at hand. Singing lower, they start comfortably in their low range, with up to three harmonics available below the 1^st formant (F1), which easily produces a rich, resonant voice. Going up the scale, a male voice would be subsequently left with two harmonics available, as the 3^rd (H3) harmonic passes the 1^st formant, and the 1^st formant mainly co-resonates with the 2^nd harmonic – the F1/H2 match. Going further up, men start having choices of F1/H1, F2/H2 and F2/H3 matching, and finally at the top of the range they end up with the “singer’s” formant – here they expertly tune the various parts of the vocal tract so that a suitable harmonic (usually H3) is boosted by a cluster of the higher formants (F3, F4, F5). The skill of clustering the formants and producing the singer’s formant is formidable and so is the effect of being heard over the orchestra.

Negotiating the Zona di Passaggio for Male Singers

When first learning how to approach the zona di passaggio, the male singers need to overcome some of their natural (human-evolutional) habits and instincts). What the untrained singers tend to do is: 

1. Being unable to “reach” for high notes, they try to carry the chest voice too high by raising the larynx, narrowing the pharynx, and starting either to yell or to “yodel” in falsetto. 
2. They try to prevent the 2^nd harmonic’s passing through the 1^st formant, and try to track H2 with F1, in an effort to maintain the bright “open voice” (voce aperta), instead of trying to switch to the closed or covered voice (voce chiusa) and allowing the vowel to darken slightly.

It is interesting to observe that the “survival” mechanisms in untrained singers are similar, whether resisting the switch from M1 (chest) to M2 (head) or insisting on tracking the 2^nd harmonic with the 1^st formant. In both instances they raise the larynx, but seemingly for two different reasons: 

1. In the first case, raising the larynx is part of the built-in instinct when singing high: shortening the resonator (pharynx) and allowing the resonator’s changing size to take the control of the pitch, because the vocal folds, maximally tightened and at the limit of the chest voice, cannot continue to do so. This alternative pitch controlling mechanism is somewhat similar to how the wind instruments are played – the resonator taking control of the vibrator – with a difference that the voice can do this only at high pitches, due to the small size of its resonator, the vocal tract, relative to, say, a clarinet. It will be long before even a trained singer, even a young professional, would be able to maintain a low larynx position on approaching the upper passaggio.
2. In the latter case, the larynx goes up in order to help the voice continue to sound open, bright and loud; larynx elevation combines with narrowing the pharynx and widening the mouth to raise the 1^st formant so that F1/H2 match can be preserved longer. While not used in classical singing, this technique, when mastered, forms the basis of musical theatre’s “belting”.

That both those vocal faults invoke a similar response can be quite confusing, and you may frequently see a demonstration of how the voice “turns”, while actually, the demonstrator shows the chest-to-head switch, or vice versa.

It would be for another discussion as to why the confusion about the events surrounding the passaggi existed for so long, but in conclusion we can suggest that the traditional assumption of fixed locations of the “turning” points, and the habit of not clearly distinguishing between the laryngeal and the acoustic events in the zona di passaggio, have no place in modern vocal pedagogy.