# Homework Help: Sound with octaves

1. Oct 1, 2009

### smillphysics

A harp from the middle ages produces a low A with a frequency of 200 Hz. What is the frequency of G on the same harp 3 octaves up?

frequency=2^(m/12)*frequency

SO 2^(m/12)*200Hz, I decided that m=9 and for each increase in an octave I though that you were supposed to mutliply 12 so in this case it would 12*12*12. The equation will read
2^(9/36)*200=237.8Hz but this is the wrong answer.
Here is the hint that is provided: Remember the order of the notes is A, A#, B, C, C#, D, D#, E, F, F#, G, G# (m=0,1,2,3,4,5,6,7,8,9,10,11,12).

I think I am just using the wrong numbers but any help would be great!

2. Oct 1, 2009

### willem2

I think they mean the G that is 3 octaves minus a whole tone above A. (it's slightly ambiguous, they could also mean 3 octaves + 10 semitones, but I took the G that was closest to the A that's 3 octaves up)

you can just count how many semitones there are between the Low A and this G, or you can find out the frequency of the G that's 2 semitones below the low A and then move up 3 octaves

An octave is 12 semitones so m = 12. that means the frequecy of a
note that's one octave up is a factor 2^(12/12) = 2 higher.