All solid objects when hit emit sounds: some have by taste and tradition been developed as musical instruments. The biggest variety are played with beaters such as drum sticks, but some instruments are similar objects which are struck together (such as cymbals and castanets). Percussion instruments are conventionally divided into ‘ pitched ’ (such as xylophones, bells and timpani) and ‘ unpitched ’ instruments (such as triangles and side drums), but in fact many unpitched instruments do give a sensation of pitch or at least of being ‘high’ or ‘low’. Drums are apparently simple instruments, but careful design and playing techniques are needed to produce pitched sounds (as with the kettledrums or timpani) and unpitched sounds as with the bass drum and side drum).