Which of the following is a characteristic of unpitched percussion instruments?

Unpitched percussion instruments are primarily characterized by their ability to produce sound without a definite pitch. Instead of creating specific musical notes, they provide rhythm and texture to a musical piece, emphasizing the beats and the overall flow of the music. This quality makes them essential in various musical genres where rhythm is a fundamental element.

The other options focus on attributes that do not apply to unpitched percussion instruments. For instance, producing specific musical notes is a characteristic of pitched instruments, which can create distinct melodies. Tuning implies that there is a reference pitch to adjust to, which is not applicable for unpitched instruments since they do not possess a definable pitch. Additionally, while unpitched instruments can vary in size, size alone does not define their classification, as unpitched instruments can range from small to large without influencing their lack of pitch.