Semitone

A measure for distances

All intervals can be measured in semitones: the minor third has three, the major third four, the fifth seven, the octave twelve. Two semitones make a whole tone. In equal temperament all twelve semitones of an octave are exactly the same size, each being the twelfth root of two (about 1.0594631) times the frequency of the one before. The measure for smaller differences is the cent; a semitone has 100 cents.

On the guitar a semitone corresponds to one fret. The fret grid follows equal temperament, with the length factor 2 to the power of −1/12, about 0.9439.

The semitone in the scale

The major scale consists of five whole tones and two semitones. The semitone steps lie between the third and fourth and between the seventh and eighth degree. The second is the more important one: it aims at the most important note of the key and carries the cadence. The tension between two notes grows the closer they lie together, which is why the seventh degree, as the leading tone, pulls so strongly to the root.

On the keyboard there is no black key between E and F or between B and C. A sharp raises a note by a semitone, a flat lowers it.

How a semitone sounds

The minor second creates strong friction because the tones lie so close together. The ear feels it as tense, unstable and pressing.

Common mistakes

• Mixing up semitone and whole tone: Between E and F lies a semitone, between C and D a whole tone.
• Placing the semitone steps wrongly: In major between degrees 3–4 and 7–8, not between 2–3.
• Equating semitone with enharmonic equivalence: C♯ and D♭ sound the same, but they are written differently depending on the key.