In music, the term note has two primary meanings: 1) a sign used in musical notation to represent the relative duration and pitch of a sound; and 2) a pitched sound itself. Notes are the "atoms" of much Western music: discretizations of musical phenomena that facilitate performance, comprehension, and analysis (Nattiez 1990, p.81n9).

The term "note" can be used in both generic and specific senses: one might say either "the piece Happy Birthday to You begins with two notes having the same pitch," or "the piece begins with two repetitions of the same note." In the former case, one uses "note" to refer to a specific musical event; in the latter, one uses the term to refer to a class of events sharing the same pitch. 250px

Note name

Two notes with fundamental frequencies in a ratio of any power of two (e.g. half, twice, or four times) are perceived as very similar. Because of that, all notes with these kinds of relations can be grouped under the same pitch class. In traditional music theory pitch classes are represented by the first seven letters of the Latin alphabet (A, B, C, D, E, F and G) (some countries use other names as in the table below). The eighth note, or octave is given the same name as the first, but has double its frequency. The name octave is also used to indicate the span of notes having a frequency ratio of two. In order to differentiate two notes that have the same pitch class but fall into different octaves, the system of scientific pitch notation combines a letter name with an Arabic numeral designating a specific octave. For example, the now-standard tuning pitch for most Western music, 440 Hz, is named a′ or A4. There are two formal ways to define each note and octave, the Helmholtz system and the Scientific pitch notation.

Accidentals

[[File:frequency vs name.svg|frame|right|Frequency vs Position on Treble Clef. Each note shown has a frequency of the previous note multiplied by $\backslash sqrt1\{2\}$]]Letter names are modified by the accidentals. A sharp music: sharp raises a note by a semitone or half-step, and a flat music: flat lowers it by the same amount. In modern tuning a half step has a frequency ratio of $\backslash sqrt2\{2\}$, approximately 1.059. The accidentals are written after the note name: so, for example, Fmusic: sharp represents F-sharp, Bmusic: flat is B-flat.

Additional accidentals are the double-sharp music: ##, raising the frequency by two semitones, and double-flat music: bb, lowering it by that amount.

In musical notation, accidentals are placed before the note symbols. Systematic alterations to the seven lettered pitches in the scale can be indicated by placing the symbols in the key signature, which then apply implicitly to all occurrences of corresponding notes. Explicitly noted accidentals can be used to override this effect for the remainder of a bar. A special accidental, the natural symbol music: natural, is used to indicate an unmodified pitch. Effects of key signature and local accidentals do not cumulate. If the key signature indicates G-sharp, a local flat before a G makes if G-flat (not F natural).