One of the thorniest issues in vocal production can be the issue of fach. Fach is a German word which literally means "compartment" or subject of study. In singing, fach refers to the issue of categorizing voices. We all know the major categories: Soprano, alto, tenor and bass. But beyond that, there are numerous subcategories which refer to specific issues such as weight, agility and the like within each major category.
Fach is used worldwide, but originally grew out of German opera houses. If a singer was categorized as a full lyric soprano for instance, that singer would only be asked to sing roles within that category.
Many voices clearly fall into one fach or another. But often, a voice will have qualities of more than one fach. Categorizing those voices can be difficult. What do you do with a woman who has a lot of smoky color in her mid range a mezzo-soprano, but has the full range of a soprano, or a male who comes into the studio who sings in the tenor range, but with a lot of "chestiness" in the midrange.
The issue is important because singing out of fach, can not only be a failure to live up to the potential of the voice, but can be damaging to the voice. A person whose voice "rings" in a higher range, but who chooses to sing in the lower range without access to much resonance can often sing with a depressed larynx, which can cause a host of problems.
So how can we determine fach in our students or for ourselves? Sometimes it is clear. A young soprano comes into the studio and she is clearly a soprano. The problem is most often faced by voice teachers in regard to "middle" voices or voices with clear tensions such as jaw and tongue tension. I think the most clear indicators of fach lie in vocal timbre and vocal tessitura.
Look to where the vocal passaggi lie when the voice is cleared on tension and the throat open. If the voice is not free of tension, work on relieving tension and correcting breath before worrying about fach.
Renowned teacher, David Jones, explores this issue (along with many others) on his website. His articles are clear and quite informative. I value and respect his opinion. You can find more information at: