Musical notation its "natural" form, which means that any sharps or flats applying to that note from the key signature or from accidentals are cancelled. Sometimes a courtesy accidental is used in music where it is not technically required, to remind the musician of what pitch the key signature requires. Following the key signature is the time signature. The time signature typically consists of two numbers, with one of the most common being "4/4". The top "4" indicates that there are four beats per measure (also called bar). The bottom "4" indicates that each of those beats are quarter notes. Measures divide
Pitch (music) of notes in the equal-tempered scale, from 16 to 16,000 Hz, is 120. The relative perception of pitch can be fooled, resulting in "aural illusions". There are several of these, such as the tritone paradox, but most notably the Shepard scale, where a continuous or discrete sequence of specially formed tones can be made to sound as if the sequence continues ascending or descending forever. Not all musical instruments make notes with a clear pitch. The unpitched percussion instrument (a class of percussion instrument) does not produce particular pitches. A sound or note of definite pitch is one where a