Two-part Vocal Closure Mechanism per Titze

Since I have not been part of the Higher Education environment for the last fourteen years, I miss out on a lot of interesting publications. What is interesting is that an article by Ingo Titze in The Journal of the Acoustical Society of America dating back to 2014 corroborates the theories I have shared on this blog relative to the necessity of deeper fold adduction. Titze’s conclusions (a culmination of more than a quarter century of research and shared research with colleagues) are so accepted in the field that they inspired research in surgical procedures to achieve the so-called rectangular glottis in phonation. I will attempt to clarify the basics as Titze explains in his article:

Titze concludes there are three muscle groups responsible for different aspects of glottal adduction: 1) The Lateral Crico-Arytenoid (LCA) pair that bring the folds to midline at the superior aspect (upper portion) of the folds. 2) Thyro-Arytenoid (TA), which includes two muscles, vocalis and muscularis, thicken the folds vertically and brings the folds in contact at the inferior aspect (lower portion) of the folds. Finally 3) Inter-Arytenoid (IA) pairs seal the posterior gap to prevent air leakage (IA is less relevant to this discussion since it only prevents leakage beyond the vibratory edge of the folds)

Titze states:

The LCA adducts the vocal processes of the arytenoid cartilages, which bring the superior edges of the vocal folds together…The bottom of the vocal folds is adducted by the TA.

But Crico-Thyroid (CT), the primary function of which is the lengthening of the folds (also called the pitch muscle) has an adductory function as well.

Titze explains further:

What role does CT activity play in registration? Its main function is anterior–posterior fiber stiffness regulation of the vocal fold tissue layers by vocal fold lengthening, but CT also plays a role in adduction. LCA and CT activity are often highly correlated in speech (Atkinson, 1978). One reason is that, when fundamental frequency is high and governed by tension in the vocal ligament (Van den Berg, 1960Titze et al., 1988), amplitude of vibration is small. Smaller amplitude requires more adduction at the vocal processes to allow the vocal folds to reach contact in vibration.

Titze confirms what I have attempted to explain here–That shallower glottal posture (i.e. convergent glottis, as Titze refer to it) requires “more adduction.”

Thinner tends to be pressed (my words).

In addition, elongated vocal folds are retracted from the glottal midline because their cross sectional area is reduced. This retraction requires further LCA adduction, which adjusts the glottis toward a convergent shape if TA activity is not simultaneously increased (Hirano, 1975). In other words, bottom adduction may not follow top adduction of the vocal folds when CT is much more activated than TA (Berke et al., 1989). At the opposite extreme, if TA activation is strong and the ligament is lax due to little CT activation, a divergent pre-phonatory configuration can be the outcome. Adduction at the top is then weaker than adduction at the bottom. For mixed registration, it is hypothesized that the two extremes are avoided with appropriate muscle balance so that a near rectangular glottis is achieved and stiffness is balanced in the tissue layers. A small convergence angle is probably not detrimental, but large divergent or convergent angles are not conducive to low-threshold self-sustained oscillation.

Titze concludes (perhaps correctly) that LCA (the primary adductory muscle) approximates only the upper portion of the folds and that TA is needed to adduct the lower aspect. He then correlates LCA and CT. He refers to convergent glottis as related to LCA dominance and divergent glottis to be TA dominant. That is one way of looking at it. Far be it from me to question the research of a top scientist far more fluent in his understanding of such matters than I am. Nevertheless, I have a suggestion purely from the singer’s point of view:

I believe that pre-phonatory postures are a result of the singer’s expectation of vocal timbre. If I imagine myself to be a bass, I will tend to expect a deep sound, which might lead to exaggerated TA activity resulting in a divergent glottis. The sound feels like it is rooted in the chest. This posture prevents the folds from closing at the upper portion, which is related to a lack of CT activity (lengthening). That imbalance results in lax vocal folds and result in a rather dull timbre. This, of course begins with the singer’s desire to sound bassy (this would work for a mezzo as well). The opposite can be said for a tenor (or soprano)–that is a tendency to desire brightness over darkness in the voice, resulting in an excessively convergent glottal posture. Naturally a tenor or soprano can desire to be excessively dark just as a bass or mezzo may seek to be excessively bright.

If we take as given that fold posture is primarily influenced by the singer’s imagined sound, then I would explain more simply that LCA is the primary adductory muscle and that the shape of the the glottis will depend on the balance between CT and TA.

Titze concludes that a balanced (or mixed) coordination in the antagonistic relationship between CT and TA will produce a desired rectangular posture that requires less adduction than the convergent (relatively pressed) glottal posture. Ideally, the folds approximate gently along the entire vertical cross-section of the folds.

The rectangular posture gives both richness and brilliance to the tone–In bel canto terms, chiaroscuro.

Titze also mentions that the extreme postures, convergent and divergent, are more stable, which is why more singers tend to find comfort in a one-sided posture (convergent or divergent). The most admired singers achieve a successful tightrope act of balancing CT and TA and regulating breath pressure as to not blow apart the gently adducting rectangular glottis and adjusting vowels in order to achieve acoustic configurations that encourage the dynamic coordination that produces the rectangular glottis.

The singer’s challenge is to figure out how it feels to access the two sides of adduction. How does appropriate TA activity feels such that it produces ideal posture on the lower portion of the folds? And how does one combine that sensation with the sensation of appropriate CT activity to close the upper portion of the folds? That is what we must achieve in voice lessons. The benefits of a mixed (rectangular) posture include an easier, more flexible tone; more dynamic transitions between registers; greater volume control; greater stamina and less wear on the folds. And more!

Lastly, health matters! Our folds’ surface is not always flat and smooth. It is usually somewhat uneven from inadequate sleep or viscosity from inadequate hydration or reflux or allergies or colds, etc. When the surface is uneven, we often compensate by adducting a little more firmly to avoid gaps in the closure (which sounds raspy and produce subharmonics). In so doing, we are creating a chain reaction that results in a more convergent glottis, lacking in depth and causing abrupt register changes. Achieving this balance is the singer’s daily work for a lifetime. Additionally, achieving balance in speaking has a great influence on the ability to achieve a mixed (Bi-stable fold adduction, per Titze’s article) posture in singing.

Copyright 4 December 2020

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11 thoughts on “Two-part Vocal Closure Mechanism per Titze

  1. Thank you! I’m not a vocal scientist, and to be honest, i haven’t been able to grasp your latest reply entirely. But thanks for the information. Definitely more food for thought. I guess when i have more knowledge, i’ll be able to understand it.

    • Neither am I, Tee Square! I’ve just read a lot over the last 35 years. I might get brave and learn physics. What I mean is that convergence (pressing) is our tendency as we go beyond the upper part of the passaggio. It’s not a range we use in everyday life. For most of us, it is difficult at first to maintain a rectangular shape up high (especially if we depress the larynx to achieve it). We’re not machines, right? We should try to fight the tendency to thin out too much by desiring a little more fullness. But let’s say that the natural tendency in the high range is to “converge”. So even the greatest tenors, like you say, would not always achieve a perfect balance and better they go a little thin than lose upper closure. Now I’m making your argument! This is good!

      • +> I guess i don’t understand when you say “I wonder if CT is not the key in convergence, which is why convergence tends to occur at higher F0s”. I’m serious. English is not my native language. And i really don’t understand why you are using “I wonder if” and then “which is”, from a language standpoint. But i’m afraid that i might be asking too much. I don’t know if i might be culturally insensitive, to be honest.

        +> And also from your reply, i just realize something. When i sing my low notes, i can sing it thin and pressed but then i’m able to gradually add more depth to it, (by trying to lower the larynx without the tongue). But then when i get to higher notes and try to do the samething, singing thin and trying to lower the larynx to get more depth, it’s not that easy. And from titze’s conclusion, it means that the higher we go the more CT gets active, which makes adding more TA adduction difficult.

        +> Here’s my opinion. Just because CT activity increases with pitch, doesn’t mean it only dominates the high range. You said that you only extrapolate from titze conclusions, right. Maybe CT gets dominated at pitch below the passagio? There’s 1 study that challenged this TA dominant low range and CT for the high range. You can read it here:

        https://ir.uiowa.edu/cgi/viewcontent.cgi?article=4994&context=etd

        Even though this study only has few participants, who are not trained singers, it’s still an interesting one i think. But all of this is just my opinion. What are your thoughts? Thanks.

      • I fluent in 7 languages and conversant in a couple others. I write in English because it was the language of my higher education. So no offense taken. Beyond that English grammar is evolving. I could present the thought as a question? “Since convergence occurs at higher frequencies, is it possible that CT (the pitch muscle) is primarily responsible for it (convergence)? I know the paper very well. The measurement of muscle activity is also a bit of a red herring (meaning impossible to confirm any conclusion). Muscular stress depends on the strength of the muscle in question and it’s “at-rest” influence on the system. The passaggio area relies on increased TA activity to counter the natural CT activity. Does that measured increase means greater work is being done by TA at that juncture? Not necessarily. What it does mean is that both muscle groups are active in achieving balance, that TA is not passive in the upper range. That paper and the many conversations that lead to it are very important. What I’m saying is that in the tug-o-war between CT-TA, it might be practical to define dominance in terms of excess in one direction (convergence) or the other (divergence). Thank you for this wonderful discussion! I don’t need to be correct. I hope to learn more!

  2. Thanks for the explaination and the discussion too! And also thank you for your positivity. It would be great to be able to conduct the same or more experiment on old and great singer. I’m looking foward for your next posts!

    • The problem in operatic singing is that we’ve lost objectivity. People always had preferences, but there were criteria to what was considered operatic. Today, the science goes backwards (e.g. “I like this sound. How can I spin the science to support my preferences?”). Beauty and viability in the hall with an orchestra don’t need to be mutually exclusive. The voices of the greats are called old-fashion and schools are more interested in teaching pop techniques, claiming opera is obsolete. But I will continue researching the old and greats! We must build on what they did. To do that we must become at least as good as they were, not abandon their model. These are challenging times!

      • Yes, i see at least one voice teacher like you described. He forced people and themselves to believe in what they think is right (two of the ways are showing just enough scientific information to be persuasive and dismissing people with different ideas). Actually, it reminds me of “this is opera” channel. I think you, I and this is opera crews all agree that generally old opera singers are better. But i really don’t like the way they dismiss other opinions without even considering it. To me that’s a sign of subjectivity. I think the first step to become more objective is to admit that we still have to learn, not to fall prey to our assumptions. And some people, like you said, purposely use assumptions and reputation to spread their belief and influence people. It would be a great to find a way to make of all the people and experts (scientific voice teachers and empirical body sensations voice teachers), who genuinely love opera, sit down and have a professionals discussions on vocal techniques.

        And i agree with you on that we should be able to do better than the olds did. Now we have more equipments but we don’t do as good, so that’s an interesting problem there. And i support you on your quest. I guess by keep reading your blogs, since i can’t do any further. Don’t forget that i care about your blogs. There’s still people out there who loves opera and its past. And i hope you can find more of those people so it makes this tough time easier. Good luck!

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