Compound metre (or compound time), is a metre in which each beat of the bar divides naturally into three equal parts. That is, each beat contains a triple pulse (Latham 2002a). The top number in the time signature will be 6, 9, 12, 15, 18, 24, etc.

Compound metres are written with a time signature that shows the number of divisions of beats in each bar as opposed to the number of beats.

https://en.wikipedia.org/wiki/Metre_(music)

https://en.wikipedia.org/wiki/Scientific_pitch_notation

soprano: C4 to A5
mezzo-soprano: A3 to F#5
alto: G3 to E5 (and contralto as F3-D5)
tenor: roughly C3 to A4
baritone: A2 to F4
bass: F2 to E4

https://web.library.yale.edu/cataloging/music/vocal-ranges