Voice classification in non-classical music chart that follows. The ranges given below are approximations and are not meant to be too rigidly applied. Some men, in falsetto voice or as a result of certain rare physiological conditions, can sing in the same range as women. These do not fall into the female categories, instead called countertenors within classical music. Within contemporary music, however, the use of the term "tenor" for these male voices would be more appropriate. Teaching voice within non-classical music is an emerging field. Up to this point, voice teachers and voice research have been largely concentrated with classical methods of singing. However,
Estill Voice Training Jo Estill has described it as "happy yelling".' Belt quality also uses clavicular breathing and has the longest closed phase with the highest subglottic pressure and the greatest glottic resistance. Estill Voice International governs the Estill Voice Training Certification Programme. There are three forms of Estill Voice Training certification available for individuals: Estill Voice Training has been adopted by voice professionals worldwide and a list of certified instructors is published by Estill Voice International. Joan Melton describes the Estill Voice Training terminology as a part of the language of singing teachers in Australia, with terms such as twang and anchoring