The question of the perfect fifth has been simmering in my mind for some time now. It started when we started investigating chord substitutions on Song Talk Radio in 2016. For that show, I looked at the Circle of Fifths as a great tool for making chord choices when writing a song. The Circle of Fifths describes tonal and chord centre relationships within the 12-note equal temperment scale we use in Western music. The most common cadence in songwriting or composing is a V – I (e.g. G-major to C-major in the key of C-major).

People, especially musicians, say that music is a universal language. This part of the question came to me when my older brother decided to learn how to play guitar, never having studied music in the past. He asked me if the scales we use and notes we use are based in anything scientifically true. So, think back to your math and science classes, we’re about to nerd out…

It’s all about the ratios

Let’s start with the most basic of tonal relationships: the octave. The octave to any note, as we know, is the same note name, either higher or lower. We can represent a note visually by a single frequency (nerd alert: this is a basic representation of a fundamental frequency, ignoring the harmonics that make up most sounds):

And its octave above is a note that is twice the frequency (purple line):

Notice how the black line (base octave) completes one cycle for every two cycles of the purple line (octave above) – a ratio of 1:2. The cycles intersect frequently and in a clear, simple pattern. This is why two notes, an octave apart, sound the most harmonious and pleasing. Regardless of the specific tuning standard (the vast majority of us use the A4=440 Hz standard), or what your base note is, this relative relationship holds true. Read more