Untuned percussion

An unpitched percussion instrument is a percussion instrument played in such a way as to produce sounds of indeterminate pitch, or an instrument normally played in this fashion.

Unpitched percussion is typically used to maintain a rhythm or to provide accents, and its sounds are unrelated to the melody and harmony of the music. Within the orchestra unpitched percussion is termed auxiliary percussion, and this subsection of the percussion section includes all unpitched instruments of the orchestra however they are played, for example the pea whistle and siren.

A common and typical example of an unpitched instrument is the snare drum, which is perceived as unpitched for three reasons:

The snare drum illustrates the three main ways in which a sound can be perceived as indeterminate in pitch:

In practice two or all of these mechanisms are frequently in effect in producing the sensation of an instrument being unpitched, but any one can be sufficient.

It is important to note that many unpitched percussion instruments do or can produce a sound with a recognisable fundamental frequency, and so can also be used as pitched percussion. The pitch of a bell is particularly strong however struck. The sound of a floor tom played with normal drumsticks is inharmonic, but the same drum played with the mallets and in the fashion of a timpani can produce a recognisable pitch, without requiring any retuning.

More radically, pitched instruments can be used to produce unpitched sounds, for example a prepared piano, or the golpe technique of flamenco music.

...
Wikipedia