Metronome
A metronome is a device that produces a regular pulse, usually used to keep a beat steady in musical rehearsal.
The metronome was invented by Dietrich Nikolaus Winkel in Amsterdam in 1812. Johann Mälzel copied several of Winkel's construction ideas and received the patent for the portable metronome in 1816. Ludwig van Beethoven was the first composer to indicate metronome markings in his music, in 1817, although the extremely fast markings he put on some pieces lead some modern scholars to suspect his metronome was quite inaccurate.
Musicians use metronomes when they practice in order to keep a standard tempo; ie, keep a steady beat throughout the music. Even in pieces that do not require strict time (see rubato), a metronome is used to give an indication of the general tempo intended by the composer. Many pieces give a tempo indication at the top of the manuscript.
One common type of metronome is the wind-up metronome, which uses a weight on the end of a rod to control the tempo (slide the weight up the rod to decrease tempo, or down the rod to increase tempo). The pendulum rod swings back and forth in tempo; mechanics inside the metronome produce a clicking sound on each swing of the rod.
Most newer metronomes are electronic. The simplest electronic metronomes have a dial or buttons to control the tempo; some can also produce a tuning note (usually A440 hertz). The button forms range from simple credit-card sized devices to the complicated "Dr. Beat", manufactured by Boss. In addition to a simple pulse, this metronome can play polyrhythms and can "count aloud", using a sampled voice.
Metronomes usually produce two kinds of clicking sound. The first one is a regular "tick" sound to mark off regular intervals within each measure, and then there is a special metallic "ching" sound to mark off the beginning of each new measure. The tempo control is used to adjust the amount of time separating each pair of ticks, but there is another, discrete, control used to choose the number of ticks in each measure. This number is usually an integer ranging from one to six, though some metronomes go up to nine, and can also have options for compound rhythm.
So if four clicks per measure are chosen, then the metronome will sound like so:
Ching!, tick, tick, tick,
ching!, tick, tick, tick,
ching!, tick, tick, tick,
ching!, tick, tick, tick, ...
Some digital metronomes, instead of making the "ching" click sound metallic, make it sound like a regular "tick" except one octave higher. Many electronic musical keyboards have their own built-in metronome function.