Perfect Octave
Definition & Properties
The perfect octave is the interval of maximum consonance, where two pitches share the same pitch class. It is the fundamental building block of the equal-tempered chromatic scale.
| Property | Value |
|---|---|
| Abbreviation | P8 |
| Semitones | 12 |
| Quality | Perfect |
| Just Ratio | 2:1 |
| Cents from Equal | 0 |
| Harmonic Character | perfect consonance |
Ear Training Reference
The Perfect Octave (P8) is commonly recognized by the ascending motion of: Somewhere Over the Rainbow (first two notes).
Practice direction: ascending — sing from the lower note up by 12 semitones.
Note Pair Examples
| Note 1 | Note 2 | Interval | Semitones |
|---|---|---|---|
| C | C (+ octave) | Perfect Octave | 12 |
| G | G (+ octave) | Perfect Octave | 12 |
| D | D (+ octave) | Perfect Octave | 12 |
| F | F (+ octave) | Perfect Octave | 12 |
Intonation by Temperament
The Perfect Octave measures 2:1 in just intonation (0 cents from equal temperament). This deviation affects ensemble tuning and instrument voicing.
| Temperament | C4 (Hz) | C5 (Hz) |
|---|---|---|
| Equal Temperament | 261.626 | 523.251 |
| Pythagorean | 260.740 | 521.480 |
| Just Intonation | 261.626 | 523.251 |
Instrument Tuning Context
The octave is the tuning reference interval — instruments tune across octaves for ensemble blend. Equal temperament octaves are exact (2:1 ratio).
Chords & Scales Containing This Interval
The Perfect Octave is present in all diatonic contexts. See the Chord Reference for chord types that incorporate this interval.
Scales
These scales include the Perfect Octave as a structural interval: