ABSTRACT
Accidentals are routinely added to certain passages to produce keys that are not reflected by the key signature, and, in the same way, grouping and accentuation patterns within a passage can create a sounding meter that is not reflected by the time signature. Meter is a musical pattern of accentuation created by two coordinated layers of evenly spaced pulses. Simple meters divide each beat into two parts, while compound meters divide each beat into three parts, and so these two categories each indicate two different layers. Once a meter is established, its tactus must be articulated almost constantly to remain a perceptual reality. Melodic groupings can be very influential in the perception of meter if they occur in immediate succession and are all the same size. Polymeter is a term referring to the simultaneous presentation of two meters, and numerous examples of polymeter are notated in scores from twentieth-century post-tonal composers.
