This thread is for educational posts about opera terms and techniques.
The passaggio is the transition between the chest voice and the head voice. When amateur/non-trained singers sing, they're using the chest voice - which is the same one we use to speak. They are breathing through the vocal cords and modulating the pitch by flexing their vocal cords, and the volume by increasing or decreasing the amount of air that is being expelled from the lungs. However to achieve more power and resonance, singers must use the head voice, which augments the sound that is coming from the vocal chords by using the spaces in their heads - mouth, nasal cavities, etc, and the way the head bones vibrate, as a sort of resonance chamber to amplify the voice. Correct use of the head voice can only be achieved by training (the amateur singer usually doesn't know how to transition to it appropriately). If singers are increasing the power with which they are producing a certain note, at one point they go as strongly as they can with the chest voice, and need next to transition to the head voice. The moment when the transition occurs - that is, they call to their help the bones and the cavities in their heads and push the power up - is called the passaggio. The higher the note, the more it will only be produced in a loud and well projected way (audible from a distance - think of those cavernous opera houses) if it's done in the head register (amateur singers are familiar with the phenomenon that makes them lose power when they try to go up the higher reaches of their range) - this is why the passaggio points are often referred to as residing on certain notes of the scale, above which singers will have to go to the next register if they want to be heard.
So, it's not just a question of volume (it's actually not entirely correct to understand this from the standpoint of volume). Usually people *can* use a higher pitch if they drop the volume. It's a question of going up in pitch but in a still powerful and very audible way - this can only be done by switching to the head register.
The main problem here is that once they make use of the head voice, it's a different set of cavities with different dimensions, therefore the sound waves produced by this additional chamber result in different set of amplitude/frequency of vibrations and sound quality of the vibrations - this other set is called another register (see below) - or in other words, when you up the pitch and go into another set of vibrations, the timbre of the voice may change.
A poorly executed passaggio, therefore, will produce a sudden change in timbre that will be unpleasant to the ear and be heard as a vocal error. The trick of the well executed passaggio is to amplify the resonance and the power, but to conserve even the same timbre so that the voice soars to the next level without sounding like a sudden break has occurred.
You've heard this, even if (in case you're a novice) you didn't know that it was a passagio error. You're familiar with tenors who push their voices up and then - eeeewww, something is not right - and you cringe! This is called a passaggio break or a register break.
Here on the other hand is, for your delight, an example of well executed passaggi:
At 1:50, and also at 3:49 and even more explicit at 4:03 and then in the long modulation from 4:28 through 4:46.
Why are we talking about a passage - passaggio? Because it is a transition between registers. A register or vocal registration is a modality of production of sound with the same vibratory pattern. Notes can be produced and sang along the same vibratory pattern. There are four types of registers - chest, middle (for females; for males, zona di passagio, see below), and head; these three are the most common ones that both males and females can produce; and then males can produce another one called fry register, and females another one called whistle register .
To make things more complex, the classical Italian school of singing recognizes two different degrees of passaggio - first and second (primo passaggio, secondo passaggio). In between them, is what we call the zona di passaggio for men, or the middle register for women.
Many vocal teachers don’t acknowledge the existence of a middle register, but might instead treat the middle section of the voice as a zona di passaggio in which the chest and head tones will become blended or mixed. There may also be some disagreement on what constitutes head voice or how it is defined, and this confusion may explain why some teachers call the lighter tone of the voice that begins at the first passaggio in female students (or any tone that is produced at pitches above the chest register) “head voice” whereas classical Italian-style teachers would refer to this register as “middle” and the register beginning around E5-F#5 (at the second passaggio) as the true head register.
The primo passaggio is the point between the speech-inflection range - that is, the range of pitches that people use to speak - and the call range - that is, the point in which they would have to yell in order to try to speak.
About the interval of a major forth above this, is the point of the secondo passaggio which is the end of the zona de passaggio and the beginning of the true head voice.
If someone tries to sing the same note and push it up in volume without readapting/reconfiguring the muscles to incorporate the head voice vibrations into it - that is, increasing volume with the chest but not doing the passaggio - the voice becomes strained due to increasing effort and discomfort.
The tenor’s primo passaggio, (typically occurring somewhere between C#4 and E4, depending on the individual's voice), lies roughly a minor or major third above that of the baritone, (usually occurring around B3 or Bb3), with his secondo passaggio occurring roughly a major fourth above his primo passaggio. Most women experience their first registration pivotal point between Eb4 and G4, and their second passaggio between Eb5 and G5, with the alto’s voice switching into the next register a little earlier in the ascending scale than the soprano’s voice would.
To make the passaggio smooth, a singer needs to allow the larynx to progressively make changes (e.g., the vocal folds should ideally change into different vibratory patterns and either elongate or shorten gradually) while ascending and descending in pitch. These progressive elongations or shortenings are physiologically called static laryngeal functions. It's by learning to control these functions that a singer can sing the passaggio without a register break. In musical terms, this gradual transition is called aggiustamento.
Breaks are typically marked by noticeable changes of tone quality and volume. For example, when a female singer moves upward from her chest register into her middle register, her tone may abruptly become thin and weak, or her voice may crack or even cut out completely. Flatting or sharping notes are other problems that may occur during the passagio.
By the way, let's define a bit more the odd/zebra registers I've mentioned above - the ones that are less common, unlike the chest/middle/head ones.
The fry register (or pulsing register) is only possible for males. It sounds like a frying, sizzling, or rattling sound. It's the lower vocal register that can be produced by a human voice. This is used to obtain pitches at very low frequency. These pitches lay below the chest register. Not all singers can access them - some basses can. In addition to this, it is damaging to the voice and frequent use will cause voice deterioration.
The whistle register (or flagiolet) occurs between C6 and D7 and is the highest sound a human voice can produce, only accessible to females. It sits above the head voice. It sounds like a whistle, obviously, thus its name. It is bright and edgy and ideally should be very similar to the head voice, to allow for a swift and pleasant transition into it. Most females except true contraltos can learn to produce the flagiolet.