Enharmonic equivalents
Five pairs to listen to: the same key twice, two different pictures. The sound is identical, the spelling is not.
Between C and D on a piano there is exactly one black key. Written down it is two things: a raised C or a lowered D. Both spellings sound the same — they are called enharmonic equivalents.
On this page every pair stands side by side twice. Listen to both pictures and you hear one and the same note; look at them and you see two different ones: the head sits a step higher or lower, and a different accidental stands in front of it. That difference is what gets measured here — the pitch from the sound, the position of the head and the accidental from the engraved image.
The spelling is not a matter of taste. It says where the note comes from and where it is going: in a key with sharps it has one name, in a key with flats another, and inside a progression it is named after its role. Choose the wrong spelling and you still play the right note, but you have written down something other than what you meant.
The black key
The commonest case and the simplest: the key between two lettered notes has no letter of its own, so it borrows one from a neighbour — from below with a raise, from above with a lower. In the picture the head moves a step and the accidental changes direction.
A sharp on a white key
There is no black key between E and F; the gap is already a semitone. A raised E therefore lands on the key that is called F anyway. It looks redundant and is not: in a scale that needs an E, the raised E is what stands there — otherwise one letter would appear twice and another not at all.
Across the octave
The same thing at the top of the octave: from B to C is a semitone, so a raised B falls on the C above. Here the head does not just move a step, it changes octave — nothing of that is audible, everything of it is visible.
A flat on a white key
And the other way round: a lowered C falls on the key below. The head then sits a step higher than its identical-sounding neighbour, with a flat in front. Such spellings are rare but they are no mistake — they turn up wherever the key demands them.
The double sharp
Two raises at once lift the note by a whole step: the head stays on its line, the key played is the neighbour. The double sharp looks like a small slanted cross and turns up almost only where a scale full of sharps has to keep its letters in order.
Two keys, the same piano keys
What holds for a single note holds for a whole key. F sharp major and G flat major press key for key the same thing — they do not sound similar, they sound identical. On paper one has six sharps, the other six flats.
Which one you use depends on what surrounds it: a piece coming from B major goes on writing sharps; one heading for D flat major writes flats. Either way it sounds the same, and either way only one of the two spellings is the obvious one.
What stands next to it
Which signs raise and lower a note and how long they hold is with the Accidentals. Which key has how many of them and how they relate is with the Tonarten.
Music symbols · Tonarten · Music notation glossary
Anotona does this for you
Photograph a page of sheet music or play the melody — Anotona finds the key, engraves the notes and transposes them into any other. Free.
See AnotonaEvery note on this page is computed, not typed in — following the rule that also makes F# major spell its seventh degree E#, not F.