[sdiy] Octaves and Decades

[John L Marshall]

Have you ever noticed that when we refer about frequency ratios of ten, we
call this as a "decade". Yet when we refer to frequency ratios of two we
call this an octave (8?) not a "bicade". This is true even in the most
technical of discussions, not related to music. In radio frequency
propagation, signal attenuation is frequently referenced over distances of
octaves (2) or decades (10).

This probably derives from 8 notes in the major scale of Western music. But,
why?