# The octave

Two notes an octave apart, with frequencies in the ratio 2:1, sound so similar that most musical traditions treat them as the same note. When men and women sing a song together, they usually sing an octave apart without noticing. The physics helps explain why: all the harmonics of the upper note are already harmonics of the lower one, so the two blend almost completely. This is why the octave is the frame in which most scales are built.

Connects to:
- [Ratios](https://mapideas.org/i/mu_ratio)
- [The fifth](https://mapideas.org/i/mu_fifth)
- [Music](https://mapideas.org/i/music)

Sources:
- [Wikipedia: Harmonic series (music)](https://en.wikipedia.org/wiki/Harmonic_series_(music))
- [What is music? Module 6, the octave, the same note again](https://sofiagallego.com/what-is-music/)

Source: https://mapideas.org/i/mu_octave · open on the map: https://mapideas.org/#mu_octave