“Most contemporary singers readily accept alternative methods of bringing the muscular actions of the two registers into play, but they are almost always compromised principles, that fall short of the ideal. The most significant, missing factor with those “quick” methods is that, they fail to grant the singer the ability to select a softly produced tone then pass on to a fortissimo dynamic, then return to the original soft dynamic. When this is the situation, there is no controlling the voice, and, the general quality of these voices remains forever “muffled,” lacking in vibrant brilliance. And, there is little variety of tonal color. And, there is seldom a tone produced (especially in the high range), which starts with a fil di voce, “a thread of voice,” which can be swelled to full volume, a vocal maneuver that is thrilling to the listener.”
Frisell, Anthony. The tenor voice. B. Humphries, 1964.