[musicman1951]

[QUOTE=Riverwolf;5276548]
I do not understand how ones voice can be in a specific key.

I think I can answer this one. When you write a song in the key of C (for example) there are no rules about which notes go in your melody. Most melodies have phrases that end on chord tones, but that's not even a rule.

So you could write a song in C that only goes as high as 3rd space C (first fret on the B string) and/or you could write a song in the key of C that goes up to the G on top of the staff (third fret on the E string). Same with the lowest notes. Most people have a rather limited range where they sound the best singing and the capo allows them to find that sweet spot for each song.

So it's not really about the Key (for singers), but more about the range. I don't have a singing key, but I sure don't want to have to sing high G's in any key!

The key does matter for having some open strings (most acoustic guitar players would prefer the sound of keys with some open strings as opposed to all bar chords - or barre, if you prefer). That would be the other main reason to use a capo.