THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

516 18. Music and Musical Instrumentslengthen the duration of the preceding note by half as much, i.e., a whole notebecomes equal in duration to a whole note plus a half note, a dotted half noteequals the duration of a half note plus a quarter note.There is no absolute time-interval standard for the duration of a tone representedby a note, and it generally depends on the performer’s interpretation of the musicwith respect to its tempo. Some compositions carry an indication of the setting ofa metronome for a quarter note. A metronome is a mechanical device that consistsof a pendulum activated by a clock-type of mechanism driven by a spring motor.At the extremities of the pendulum swing an audible tick is produced. The intervalbetween ticks can be adjusted by moving a bob on the pendulum arm: the furtherthe bob is located from the fulcrum, the longer the duration between ticks, andvice versa. The pendulum itself is graduated in ticks per minute. The numbersusually indicate the number of ticks per minute, the interval between ticks usuallyspecified as that of a quarter note or, in some cases, half notes. Modern versions ofmetronomes use electronic means to generate ticks. The metronome setting setsthe rate of movement or tempo of the music. Instead of metronome settings, thecomposer may specify one of a number of terms to designate tempos. Commonlyused terms to describe tempos are as follows: Largo: Slow tempo Andante: Moderately slow tempo Moderato: Moderate tempo Allegro: Moderately quick tempo Vivo: Rapid tempo Presto: Very rapid tempo18.4 Time Signature NotationA musical selection’s time signature is specified at the beginning of the staff bya fraction, as illustrated in Figure 18.10. Common time signatures include 2/4,3/4, 4/4, and 6/8. The denominator indicates the unit of measure (i.e., the noteused to define a pulse). The numerator stands for the number of these units or theirequivalents included in a measure (i.e., the interval between two vertical linesacross the staff).Figure 18.10. Time signatures for 2/4, 3/4,Cor4/4, 6/8, and 9/16 times.