math question about waveforms an octave apart...

Hi all,

I have a synth with two tri~ objects, one an octave lower than the other. I have a knob on my midi controller that I am using to pitch shift down the first tri~ object on a scale of 0-500 freq. What math function could I use to convert that scale so it would perfectly line up with the tri~ an octave lower?

Thank you. Nick D.