Dear Lloyd
Thank you for a very succinct and coherent posting on registers and vocal fold function. I would agree with much of what you have written but I do have difficulty with the idea that the vocalis is active only in chest voice and that resistance to the cricothyroid in head voice comes solely from the ligament. Human physiology is based upon agonist and antagonist: two muscles, or sets of muscles, contracting in opposite directions to control movement finely. Both sets are active but to varying degrees. I have always understood that ligaments cannot contract; therefore, the vocal ligament cannot act as antagonist to the cricothyroid, just a safety strap stops you falling further but can't pull you back up. Were the vocalis to cease to act in head voice, would that not make the cricothyroid unique in acting with no antagonist? It seems to me that pitch change could then be achieved only by increasing or decreasing subglottal pressure or airflow, which would limit the singer's ability to 'disconnect' pitch change from dynamic change. For example, if the singer's vocal folds were now stretched to the point where the ligament was activated, the only way to raise pitch would be to raise subglottal pressure (may I crudely say, "blow harder") but this would also increase loudness, so how would the singer float a high note pianissimo?
My understanding from Hirano's work is that stretching the vocal folds by the cricothyroid acts to stretch both body and cover, so that full stretch (such as to take up the ligament) would mean stiff cover and (without any antagonist to the cricothyroid) no way to reduce the cover's stiffness. Therefore, how would changes in timbre occur? If I have a singer in my studio who is pushing too hard on high notes, I aim to have him reduce the effort (and this applies to low and middle notes too), and I postulate that what I am doing is both reducing the total tension (and adductive force, as well) and changing the balance to be 'more contribution from the vocalis, less from the cricothyroid' so that the vocal fold tension is as required for that pitch, that loudness, that timbre but the tension in the cover is less. That is, producing the same amount of vocal fold tension/mass with a shorter vocal fold so that the cover is looser. This is my understanding of different timbres on high notes. If the vocal fold tension/mass on high notes is produced solely by the cricothyroid with no antagonist, I cannot see a) how pitch could be changed, b) how pitch and loudness could be separated, and c) how different timbres could be obtained.
For completeness of discussion, I should add that stretching the vocal folds will induce passive tension (antagonism) in the vocalis but being passive this would not provide the active antagonist needed by every agonist for fine co-ordination.
In brief, I believe both vocalis and cricothyroid should be active at all times in singing and that the balance between their contributions is significant to the timbre.
With regard to register transition during loud or soft singing, I have always found the transition to be more challenging when singing softly than when singing loudly. If my simplistic assumptions on vocal fold function are fundamentally accurate, I would have to conclude that my habit during an upward scale softly is to reduce the contribution of the vocalis too soon, replace it with greater contribution of the cricothyroid, then increase airflow/pressure to counteract the drop in loudness due to decrease in upper partial energy in the source spectrum resulting from stiffening of the cover. To say that in a more complicated way, I change the balance from chest (which is louder, and I am careful to use the perceptual term 'louder' here) to head too soon and short-change myself by mistaking use of a lighter timbre with singing softer: I reduce the richness instead of just singing more quietly.
Unfortunately, my reply is not nearly so succinct or lucid as your posting. These are speculations based on matching what I think I know from reading with what I think I know from working with my own voice and working with others' voices. There are many, many gaps. Thank you for the opportunity to wrestle a little more with this conundrum.
Kind regards
Sally
|