Breath pressure (Sub-Glottic Pressure) is how much air is in your lungs when you begin to make sound. Breath pressure goes lower as you run out of air. If you push, pull or otherwise activate the abs while at the same time resisting the collapse of the ribs, you can keep the breath pressure increasing so you stay at about the same level of pressure (volume) even though you have less air in your lungs. [Sometimes called in classical training “appoggia”.] You can even do a crescendo at the end of the airstream if all of those muscles are strong enough to keep pushing what’s left out harder and harder. This is in Dr. Johan Sundberg’s book. All of this together is “breath support”. The measurement of the air movement is done by a ‘Rothenberg inverse filter’ which measures Sound Pressure Level (SPL) through changes that take place in the mouth using “pah” as the standard sound.
Open-closed quotient is how long your vocal folds stay together in each cycle of vibration. [A440 = one/four-hundred and fortieth is a cycle of vibration of the folds as they open and close in a wave.] That’s different than when they make contact (partial closing). The longer they stay together, the higher the closed quotient. We associate this with chest register or mix at high volumes, or maybe even any loud sound. Long open quotient is associated with head register. The dynamics between the folds and the air pressure is variable so this is why “breath support” taught as “one behavior” is misleading. How the breath moves while you sing depends on what kind of singing you are doing. Counter tenors have the lowest (sub-glottic pressure) and dramatic opera tenors and sopranos the highest, with belters right after that. Everyone else is different and in between. This is from research done by Johan Sundberg about four years ago.
Depth of vocal fold vibration. In most cases the full depth of the fold is operating in chest register. Only the upper edges vibrate in pure head. This would effect also the open/closed quotient and the breath pressure below the folds. There is much discussion about this now with the scientists. Air that flows out over the vibrating vocal folds is called “trans-glottal” airflow. The glottis is the space between the vocal folds. When the glottis is closed, the vocal folds are touching.
All of these things are observed phenomena. The have been observed by scientists. Knowing about them is good. It will not help you sing better. It cannot even help you avoid singing poorly. You cannot do them, they happen. THIS IS A CRUCIAL THING TO UNDERSTAND.
You can learn to “do” movements in your throat, although in the best scenario, the movement starts happening because the exercises stimulate it and then you notice, “Oh, I can feel something moving around when I sing that.” Reid calls it register rotation, Vennard calls it the dynamic larynx. Without this movement it is nearly impossible to express deeply felt emotions easily.
If the muscles of the base of the tongue are loose enough to move in response to messages from the brain to allow for changes in pitch and vowel, the thyroid cartilage will rotate (tilt) by being pulled on by the crico-thryoid muscle as you ascend in pitch. The two will touch at the front of what we see from the outside as being the “Adam’s Apple”. If everything is flexible inside, the larynx will also drop slightly down on a closed (dark, covered) vowel and raise a bit on a brighter vowel. This changes the shape of the vocal tract (the resonance or “placement” of the sound) and allows a smooth, gliding transition from one register to another (chest to head, head to chest, mix in-between). In mid-range, if the vocal folds are free to adjust in length and depth and the breath pressure is constant but can also adjust, a smooth register transition will be possible. This also implies that vowel shape has to change along with registration in order to maintain comfort. This is why a “fixed low larynx position” cuts off high notes and makes soft high singing very hard. It gives the voice fullness, but it sacrifices brightness and ease at the top. The ideal “home base” configuration for the most natural “default” of the mechanism in everyone is allowing the registers to roll through from chest to mix to head on their own as you ascend in pitch or do the reverse going down. Knowing about it still doesn’t help you do it. : (
Head voice, head register, head tone, head vibration (pick a spot) are all the same, if understood incorrectly, however, head voice may or may not be associated in the mind with head register, hence the confusion. If you are singing a “connected falsetto” as a guy….it sounds like falsetto but you could crescendo into a full sound without a break. If you could not crescendo without “breaking” it is considered “pure falsetto”. Head voice (voix blanche) or “re-enforced falsetto” is something a classical singer might do at the end of “La Fleur” , Jose’s aria from Carmen, although you don’t that much anymore. Listen here to Jonas Kaufmann:
The first three notes are in head voice and then he goes smoothly into his full voice. He does a pretty good job of singing in soft chest mix at the end but doesn’t really go into head. Who cares? It’s beautiful singing, very expressive and these days very rare.
In commercial music, NO ONE CARES. Franki Valli was singing in a squeezed falsetto. Worked for him!