APPENDIX 2 ACOUSTICS
Acoustics (from the Greek verb akouo or “to hear” or “to listen”) is a branch of science that studies sound. In
music, sound is defined in four ways: pitch, duration, volume and timbre. We studied these musical components
in the earlier modules; in this appendix we will briefly discuss the science of these components.
Pitch (Frequency)
Sound is determined by the number of vibrations per second (frequency) created by a vibrating object. If the
vibrations are regular, a pitch is produced. Random vibrations produce non-pitched sounds, for example,
the sound of a jet or a tambourine.
Note:
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Frequency may be defined as the number of times a pattern repeats (or cycles); frequency is measured
in Hertz (Hz), which is the number of cycles per second. Humans hear sounds between 20 Hz and 20,000
Hz.
Frequency determines pitch; the higher the frequency, the higher the pitch. Today we use 440 Hz (the A
above middle C) as the pitch for tuning.
Octave pitches are created by doubling or halving a frequency. For example, a piano string vibrating at 220
Hz will produce the A below middle C. A string half as long will vibrate at 440 Hz, or twice the frequency,
and produce the A above middle C, or an octave higher. In fact, all octave pitches vibrate at a ratio of 2:1;
therefore all A’s will be a multiple of 440.
Duration
Musicians refer to rhythmic values when speaking of duration: how long does a note (or silence) last? Duration
also may be affected by the attack, decay, sustain and release of the note.
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The attack is the initial creation of the sound. For example, is the flute “tongued” giving the note a sharp
attack? How does the pianist strike the key: with a sharp accent or a gentle drop?
The decay is the decrease in volume after the attack. Some instruments like wood blocks have an immediate
decay and the sound disappears immediately after the attack. Other instruments like the organ can maintain
their volume indefinitely.
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A P P E N D I X
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The sustain is the length of time before the sound becomes inaudible. This aspect of duration is different
from the rhythmic value of a note. For example, the quarter note receives one beat.
The release is end of the note. On a piano, the key is released; the flutist stops the flow of air.
Volume (Intensity)
When a sound is created, air molecules are set in motion, resulting in vibrations; the higher the frequency of
vibrations, the higher the pitch. The volume of the sound, however, is determined by how much the air molecules expand and compress (the amplitude), which affects the air pressure. The greater the increase and decrease
in air pressure, the greater the sound’s intensity. A sound wave’s intensity is related to its amplitude. Musicians
use the term dynamics when talking about intensity.
Note:
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Intensity is measured in decibels (dB) beginning with 0 dB, which is the softest sound that humans can
hear.
Examples of sounds measured in dB include a whisper (20 dB) to the sound of a large orchestra (98 dB).
Sounds at 160 dB will cause instant and irreparable hearing loss.
Color (Timbre)
Each sound created by an instrument consists of more than one frequency. These frequencies are not heard as
discreet ones, but as a combination of the frequencies. The instruments from around the world are classified by
type:
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Aerophones (flutes, brasses, reeds) where air vibrates through a column;
Chordophones (stringed instruments) where a string vibrates;
Idiophones (percussive instruments such as bells and shakers) where the instrument produces the sound
(idio means “itself”);
Membranophones (drums) where a membrane vibrates.
Similar instruments within each classification have a similar series of frequencies. This aspect of sound is called
timbre, or color; for example, a trumpet has a distinctly different sound from a violin, and a singer sounds
noticeably different from a sitar.
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