While the countertenor is almost universally recognized as a voice category, it is not a voice type in the strictest sense. Except for a few very rare voices (such as the American male soprano Michael Maniaci or singers with a disorder such as Kallmann syndrome), countertenors generally sing in the falsetto register, sometimes using their modal voice for the lowest notes. The countertenor voice is therefore a product of the application of a specific technical approach, not the result of the biological factors which have long been credited with determining the other voice types included on this list. These factors include vocal-fold length, thickness, and other elements of laryngeal proportions. All countertenors, save those rare examples previously mentioned, also fall into the traditional male voice categories, such as tenor and bass.