Regardless of the methods adopted or the theoretical stance assumed, however, one fact stands clear: the difficult transition points experienced by singers, which have led to such pedagogic panaceas as “hooking,” lifting “up and over,” getting the tone “forward,” “high and low placement,” and “covering,” all direct themselves to difficulties that are related to registration.

The mechanistic training methods based on the precepts noted above have not proved successful. Few singers appearing before the public could justly be said to have more than marginally fulfilled their potential, and the throat constriction that is the logical outgrowth of such practices is encouraged rather than cured by these techniques of tone production.

In the final analysis, vocal training and artistic singing should be founded upon principles which agree with the laws of physics, physiology, and acoustics. Short cuts are not the answer. What is patently clear is that all music, whether dramatic or lyric, and whether composed by Monteverdi, Mozart, Wagner, Verdi, Strauss, or Berg, can be best be sung when the mechanical parts responsible for producing vocal tone work in accordance with nature’s laws. The practice of covering does not conform to those laws.

The history of great singers and singing is replete with names of those who used their voices lyrically and in the true Bel Canto tradition even when the voices were heroic in size. Frequently, these voices are described as being “unusual” and “exceptional,” but this fact remains: while they are rare, these singers nonetheless are exceptional not because of any anatomical superiority, but because they use their voices exceptionally well, and avoid such unnecessary and inhibitory devices as “covering.” Duprez had a short career. He was able to sing at one dynamic level (high), and he had little flexibility. His was at best a limited technique. In large part, those limitations were and are the equivalent expression of “covering.”

Cornelius Reid, Dictionary of Vocal Terminology