Unison
Two notes at the same pitch, which sounds like one note until it is not. Detune it here by a few cents and you hear why an interval of nothing still matters.
- 0 semitones
- 1:1
- no distance
related pages
What it is
Zero semitones. Both notes are the same pitch, and their frequencies are identical. Play them on two instruments and you do not hear two notes: you hear one note with a different colour, because the two sources reinforce each other.
How to recognise it
There is nothing to recognise until something goes wrong. Pull one of the two notes a few cents away and a slow beating starts, and the further you go the faster it beats.
That beating is the single most useful thing on this page: it is how every tuner, every piano technician and every singer in a choir checks their pitch.
Where it shows up
In unison singing and doubled guitar parts, where tiny differences make the sound wider. In chorus and detune effects, which are a unison deliberately knocked out of line. In every tuning decision you ever make.
What it gets confused with
With the octave. Two notes an octave apart also fuse into one sound, but there the upper note is twice the frequency and you can still hear two pitches if you listen.