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What Are Flat Notes in Music?
Flat notes are notes that sound a semitone lower than notes that appear on the lines and spaces of a musical staff.
- As an example, the note B is represented on the third line of the treble clef staff. The note B-flat is indicated with that same notehead with a ♭ symbol placed to the left of it.
- The ♭ symbol universally indicates a flat note. It tells a player to sound a pitch half a tone lower than the written note. For instance, the following image indicates the note A♭ on the treble clef.
What Is the Difference Between Sharp Notes and Flat Notes?
Sharps and flats fall into a musical category called “accidentals.” They represent alterations to “natural” notes like C or D or B.
- On a piano keyboard, all of the black keys can be notated as “flats,” and can also be notated as “sharps.”
- Any note can be a sharp or a flat—even white keys on the piano. For instance, the note B (a white key on the piano) can also be notated as C-flat. The note D (also a white key on the piano) can be notated as E double-flat.
There are two ways to think of sharps and flats: acoustically and in terms of music theory. As an example, let’s consider two notes: D#4 (the pitch D# in the fourth octave on a piano) and Eb4 (the pitch Eb in the fourth octave on a piano).
Acoustically, D#4 and Eb4 are the same notes. They both represent sound waves vibrating at a frequency of 311.13 Hz in standard instrument tuning. As such, if you were to play a D#4 and an Eb4 on the piano, you would be striking the same exact piano key. A person with absolute pitch would not be able to tell you one note is a D# while another is Eb.
When Should You Use a Sharp vs. a Flat?
In terms of music theory, a note would be deemed either sharp or flat based on what key it appears in. This is because Western music is divided into groups of sharp keys and flat keys.
- C major is neither a sharp key nor a flat key. It contains no accidentals—only natural notes. (The same is true for its relative minor key, A minor.)
- From C major, we can follow the circle of 5ths and cycle through multiple “sharp keys”: G major, D major, A major, E major, B major, F# major, and C# major. Additionally, the relative minor keys of these key signatures are also “sharp keys”: E minor, B minor, F# minor, C# minor, G# minor, D# minor, and A# minor.
- We can also cycle in the other direction from C major, and follow a circle of 4ths through multiple “flat keys”: F, Bb, Eb, Ab, Db, Gb, Cb. As was true for sharps, the relative minor keys of these flat keys are also considered “flat”: Dm, Gm, Cm, Fm, Bbm, Ebm, Abm.
As a general rule, “flat keys” get flat accidentals and “sharp keys” get sharp accidentals. Thus, to return to our notes D# and Eb, D# traditionally appears in sharp keys, such as E or B. Eb traditionally appears in flat keys, such as Ab or C minor.
So what’s more important: the acoustics or the music theory? Ultimately, it’s the acoustics, since that’s what listeners will experience. A listener doesn’t care if a piece of sheet music says D#4 or Eb4: she will hear the same exact audio frequency from her seat in the audience. And at the end of the day, that’s the most important thing about music: how it sounds to an audience.
Learn more about music theory in Itzhak Perlman’s MasterClass.