Sorry if this sounds stupid

I would just like to know if someone can explain someting to me about frequencys.
If I have a sound that is 44000hz like a piano note "A" and then I put it into mmf and tell it to play at 44000hz. It will play at one octave up from 44000hz.
So how does mmf work out it's freq if a sound already has a freq.
and why are the freq limited from 100 to 100 000.
Thanks.