A note is a sound with a fixed pitch. Western music names its notes with seven letters, A through G, repeating in every octave.
Pitch is how high or low a sound is, and it is measured in vibrations per second (hertz). When a string or a speaker vibrates 440 times per second, you hear the note called A4, the tuning reference of most modern music.
The same note name repeats up and down the range: A exists at 110 Hz, 220 Hz, 440 Hz and 880 Hz. Each doubling of frequency is one octave, and notes an octave apart sound so alike that music treats them as the same letter.
| Note | MIDI | Frequency |
|---|---|---|
| A3 | 57 | 220.00 Hz |
| C4 | 60 | 261.63 Hz |
| E4 | 64 | 329.63 Hz |
| G4 | 67 | 392.00 Hz |
| A4 | 69 | 440.00 Hz |
| C5 | 72 | 523.25 Hz |
| A5 | 81 | 880.00 Hz |
Common questions
What is a note in music?
A note is a sound with a fixed pitch, named with the letters A to G. The pattern of names repeats every octave.
Why is A 440 Hz?
A4 = 440 Hz is the modern international tuning standard. It is a convention, not a law of physics; ensembles occasionally tune slightly higher or lower.