Fill in the Blank. (mathrm{A}(mathrm{n})) ___________ is the interval between any two frequencies (left(f_{2}-f_{1} ight)) whose frequency

Fill in the Blank.

\(\mathrm{A}(\mathrm{n})\) ___________ is the interval between any two frequencies \(\left(f_{2}-f_{1}\right)\) whose frequency ratio \(\left(\frac{f_{2}}{f_{1}}\right)\) is 2.