The thickness of the vocal folds do not fit into two static categories such as thick or thin nor M1 and M2. The vocal folds change their length and their thickness in a continuous manner as the sung pitch is raised or lowered. In this they meet the myoelastic theory of vocal fold function as well as the aerodynamic theory that emphasis the Bernoulli Principal to assist with vocal fold closure.
A newer element was introduced by Ingo Titze that addresses the effect on the vocal folds of a standing wave in the vocal tract. When the tendency of the vocal tract to resonate desecrate frequencies (formants) is matched to phonated tone that contains some of these frequencies a standing wave is created within the vocal tract. This standing wave will, because it has inertia, resist both the opening and closing of the vocal folds and in this way greatly assists them in transferring their energy into the vocal stream (please see footnote). It is as if the standing wave is a pneumatic spring into which the vocal folds move and that spring works in both directions, open and close. The gives the vocal folds stability to function more freely in their shortening/thickening and lengthening/thinning actions.
But, the crucial element of this progression is the tuning of the vocal tract to match available harmonics in the phonated tone. Each pitch we sing will have a broad spectrum of harmonics if the tone is produced efficiently by the vocal folds. For example, a breathy tone has few harmonics because the vocal folds do not come together for a sufficient length of time. This is also true of falsetto; the anterior of the vocal folds are not completely closed.
Given a well produced tone from the phonation process (phonated tone) the singer must be trained to make adjustments in the vocal tract in order to match the vocal tract potential frequencies (formants) to the actual frequencies produced by the phonated tone. When this occurs the vocal tract will increase the loudness (amplitude) of those frequencies. In most cases only about two or three frequencies are so amplified. And, surprisingly it is seldom the fundamental that receives this boost in loudness.
The lowest two formants of the vocal tract determine the vowel that is being sung or said. And each vowel or modification of a vowel gives different formants. The two lowest formants are called the vowel formants for obvious reasons.
As the voice ascends in pitch an one vowel it will eventually reach a point where that vowel can no longer find a phonated tone harmonic to resonate. At that point the vocal tract no longer has a standing wave and there is no longer the benefit to the singer of the pneumatic cushion to stabilize the vocal folds. As a result, the vocal folds tend to become asynchronous and do not open and close as a unit. The result is a ‘break’ in the voice and we have now entered into the first sign of a passaggio.. This discomfort will usually continue for about a minor third interval as the pitch continues to rise and then, magically, we find ourselves in another register where the same vowel is once again able to resonate a harmonic of the sung pitch. Or we are not able to find a new register.
In short, passaggi and registers do exist but they exist more because of mis-tuning the vocal tract such that it does not match the harmonics of the phonated tone. If the sung vowel is changed or slightly modified when the ascending pitch enters that area where the vocal tract is unable to resonate the original vowel correctly, the problem of the passaggio will likely not appear.
Try this. Sing an ascending octave that goes over your passaggio on the vowel /a/. As you feel yourself approaching your passaggio, change the vowel to an /i/ or /e/ (or /u/ or /o/) and when above your passaggio go back to the /a/ vowel. Done correctly you will very likely not experience the clumsiness of your passaggio but instead be able to sing smoothly over it. The reason? By changing to the more closed vowel at the beginning of the passaggio you re-tuned the vocal tract to a vowel whose formants will match some of the frequencies of the sung pitch in that area.
Footnote from Reg on “The Vocalist”.
“I’d have said that it alternately –assists- and –resists- the operation of the previously un-stabilized folds. As I’ve mentioned before, the process of feedback not only greatly reduces the source impedance, it brings stability to that impedance as well”.
Dear Lloyd,
You have been and are one of my pedagogical heroes. I have taken many first steps through our interaction over the years. What you write here is what those of us who understand the science accept to be true and logical.
The only thing that I find problematic here is that this model assumes that every voice is ready to accomplish this gradual thinning and/thickening of the vocal folds. And this is simply not the case. The dynamic interdependence of CT/TA must be learned in most cases. As must the interdependence between vertical contact area (CT/TA dynamic) and fold closure. There are many different possible fold postures that will result in a desired pitch, i.e. very pressed, slightly pressed, slightly breathy, very breathy and every thing in between. And as fold closure depends also on contact area (vertical mass), these various adduction issues have a bearing on contact area as well. The acoustical issues are moot if the myoelastic component is not optimal. Formant tuning can occur in a very inefficient voice or a very efficient one.
Spectrography is the easiest thing to observe, but it is not all encompassing. I sang two very different sounds the other day which produced practically identical spectrograms.
Spectrograms can tell us a lot, but we need to consider many things in addition to what is usually considered. For example: (A) F1 and F2 not F1 or F2, meaning the passive formant’s role is important in a balanced tone. The value of F1 is also important in a note that is F2-dominant and vice versa; (B) The fact that the female voice exhibits a sine wave beyond the second passaggio does not mean it is a falsetto production. Some scientists go as far as to call the female high range falsetto in nature. There is much that is too simplistically propagated in the world of pedagogy.
What you write here is so significant and yet over the heads of the majority of people who teach voice. That alone makes the post extremely important and I will send people to this link to experience your excellent, no-nonsense, informative writing. But as teachers who have a foot in the science side, we must begin to talk about these things in a far deeper level. We should be talking about the paradoxical nature of the voice, the interdependence of source and filter, the possibility of full-closure via supra glottal inertia while the folds may remain slightly open, etc.
For my part, I have a deeper interest in the physical conditioning of the vocal instrument, whereby the musculature is fit and flexible and ready to respond to the needs of the singer. The science of acoustics produces great results in voices that can already produce a powerful source tone. Acoustics is a multiplier. Proper tuning of the vocal tract increases efficiency commensurate with the nature of the source tone. A weak source will not become an amazing tone because of good acoustics. I have come to find that developing an excellent creates the conditions that makes good acoustics almost miraculous.
Finally, I must say there is “thin or thick” folds when F0 is constant. There is an optimum contact area that corresponds to the most efficient medial pressure. In a constant F0, the close quotient depends on two factors: 1) depth of contact area which contributes to the amount of time required for the fold to close fully in the first part of the mucosal wave 2) medial pressure which contributes to how long it takes the fold to peal open. Both contribute to the close phase. Where fold depth is extreme and medial pressure is also extreme F0 will lower in frequency relative to the given pitch. Finding an balance between the two is the goal and most singers do not have this innately. I submit that what we deem acceptable in our times does not compare well with what was expected in earlier times, simply because we do not spend enough time in conditioning but rather almost the entire time in coordination. It is like asking a runner with unconditioned legs to break a word record simply by applying ideal form. Ideal form only produces world record pace when the runner has perfectly conditioned legs.
With the greatest of respect, I do not argue with the facts you present here but only that the discussion needs to go deeper.
With great admiration,
JRL
Lloyd!
Thanks for a great article! As someone said above, you are a pedogogical hero. I still use much of what I learned from you- particularly Bert Coffin – with my choirs. and folks I’m coaching.
This article immersed me in the vocal acoustics I used to enjoy so much in college,
Hope all is well,
Scott Kovacs