This is the first and oldest instrument.
The ability to sing is the simplest instrument to use and the hardest instrument to master.

According to the Golden Encyclopedia of Music  There are three ranges in men's voice And three ranges in women's voices:
Tenor	Soprano
Baritone	Mezzo-Soprano
Bass	Alto
Occasionally people can sing beyond these normal ranges due to natural ability or practice, and some people cannot reach all the notes in a range. Also male falsetto voice may give an octave above the top limit of a range.

In the SCA voice is the most common of all instruments. 

In period, vocal music was written in many styles

Chant - The origins of chant go back to antiquity. Hebrew and Greek music likely lead to the use of chant in the Christian church. Gregorian chant is the most commonly known but not the only form of chant practiced in period. Originally each group of Christians in the early church developed it's own form of chant. 

Opera - The beginnings of modern opera are seen in period, Dafne, written by Jacopo Peri and performed as private entertainment for Count Corsi in 1597 (Florentine), and the first one, Euridice, publicly performed in 1600. Euridice was written by Peri and Guilio Caccini and performed for the wedding of Henri IV of France and Marie de'Medici in Florence.

Secular - Every culture developed it's own vocal music and it was used for every occasion. Every class of people sang; parody, love, criticism, teaching, grief, and every other conceivable emotion or occasion was expressed in song.