Why do two notes an octave apart sound like the same note?
A low A and a high A are completely different vibrations, yet your ear files them under the same name. Not everyone's ear does.
▶ Start the storyTwo notes an octave apart sound like "the same note" because one vibrates exactly twice as fast as the other, and that 2:1 ratio makes their harmonics line up. If one A vibrates 440 times a second, the A above it vibrates 880 times and the A below 220. After playing the same note twice, the octave is the simplest relationship two notes can have, and the ear tends to hear the pair as essentially one sound in two sizes.
Every one of these is an A
Hz
| Frequency | |
|---|---|
| A | 27.5 Hz |
| A | 55 Hz |
| A | 110 Hz |
| A | 220 Hz |
| A | 440 Hz |
| A | 880 Hz |
The proof is everywhere. Western music gives both notes the same letter name. And when men and women are asked to sing "the same" note together, they usually end up an octave apart without noticing, each in their own comfortable range.
But here is the twist. Researchers from MIT and the Max Planck Institute played two- or three-note tunes to the Tsimane', who live in a remote part of the Bolivian rainforest, and asked them to sing them back. Americans, especially musicians, instinctively sang the tune an exact number of octaves higher or lower. The Tsimane' kept the shape of the melody, but their starting note had no link to the one they heard. The octave may be a natural gift, but it seems we have to hear octave-based music to unwrap it.
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Recap
Double the frequency and the harmonics line up, so the ear hears one note in two sizes, at least if it grew up with octave-based music.
Surprising fact · Listeners with little exposure to Western music, like the Tsimane' in Bolivia, don't automatically hear octaves as the same note.
Sources (3)
No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.