Interval reference
Perfect unison
Same letter · 0 semitones · C → C
A perfect unison spans the same letter name and 0 semitones. Both halves of that description matter: the number comes from the letters, the quality from the exact size.
Starting on C, a perfect unison reaches C. Its shorthand is P1, and traditionally it counts as perfect consonance.
How big it is
Hear it from any note
The explorer starts on C up to C. Play it one note after the other and then both together — the two ways a perfect unison turns up in music — then change the bottom note: the distance stays the same while the spelling follows the letters.
Turned upside down
Move the lower note up an octave and a perfect unison becomes a perfect octave. The two numbers add up to nine, and the quality flips — major with minor, augmented with diminished, while perfect stays perfect.
Where you meet it
- Two instruments playing the same melody at the same pitch
- Doubling a line at the unison rather than the octave
From every starting note
| From | Up a perfect unison |
|---|---|
| C | C |
| C♯ | C♯ |
| D | D |
| D♯ | D♯ |
| E | E |
| F | F |
| F♯ | F♯ |
| G | G |
| G♯ | G♯ |
| A | A |
| A♯ | A♯ |
| B | B |