Sixteenth Note

A sixteenth note lasts half an eighth note and a quarter of a quarter note. In 4/4 time, where the quarter note gets the beat, four sixteenths fill one beat and sixteen fill a bar. How long that is in seconds depends on the tempo: at 120 beats per minute a sixteenth lasts an eighth of a second, which is why runs of sixteenths read as "fast". The filled head and the stem are the same as on a quarter note; each flag halves the value, so one flag is an eighth, two flags a sixteenth, three a thirty-second.

In printed music, sixteenths that belong together, usually within one beat, are joined by two horizontal beams instead of flags, and in a mixed group of eighths and sixteenths one beam runs across all the notes while the second, shorter beam touches only the sixteenths. The single flagged shape you see here is what a lone sixteenth looks like.

Why do some people call it a semiquaver?

Sixteenth note is the American name; semiquaver is the British one. Both systems describe the same note. American names are fractions of the whole note (whole, half, quarter, eighth, sixteenth); British names are a chain of older words: quaver for the eighth, semiquaver for half of it, then demisemiquaver and hemidemisemiquaver. Other languages have their own names: Spanish semicorchea, Portuguese semicolcheia, French double croche, Italian semicroma, German Sechzehntelnote.

The shape comes from mensural notation, the European system that from the late 13th century used distinct note forms to fix rhythm in music with several independent voices. Ever shorter values were added over time, and this note's ancestor, the semifusa, was in use by the 15th century; Franchinus Gafurius's treatise Practica Musicae, printed in Milan in 1496, is cited as an early record of it. The English printer John Playford is credited with grouping sixteenths under two beams in the 17th century. One leftover of that history: in Spanish and Portuguese today, semifusa no longer names this note but a much shorter one, the sixty-fourth.