Chapter 24

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Chapter 24 Sound

• 24.3 Sound , Perception and Music
• pp. 590-597

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24.3 Sound perception and music

• When you hear a sound, the nerves in your ear
  respond to more than 15,000 different frequencies
  at once.
• The brain makes sense of complex sound because
  the ear separates the sound into different
  frequencies.

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24.3 Sound perception and music

• A frequency spectrum shows the amplitudes of
  different frequencies present in a sound.

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24.3 Sonograms

• More information is found in a sonogram which
  combines three sound variables
• frequency,
• time, and
• amplitude (loudness).

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24.3 Sonograms
Which letter represents a soft sound lasting 5
seconds?
What is its frequency?
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24.3 How we hear sound

• The parts of the ear work together

1. When the eardrum vibrates, three small bones
   transmit the vibrations to the cochlea.
2. The vibrations make waves inside the cochlea,
   which vibrates nerves in the spiral.
3. Each part of the spiral is sensitive to a
   different frequency.

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24.3 Sound protection

• Listening to loud sounds for a long time causes
  the hairs on the nerves in the cochlea to weaken
  or break off resulting in permanent damage.

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NOISE POLLUTION

• When noise reaches a level that causes pain or
  damages the body it is called noise pollution.
• Noise pollution can damage the inner ear, causing
  permanent hearing loss.
• Noise pollution can contribute to sleeplessness,
  high blood pressure and stress.

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WHITE NOISE

• This is an equal mixture of all frequencies (like
  white light is a mixture of all colors).
• White noise machines are used to calm people and
  help make them sleep.

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24.3 Music

• The pitch of a sound is how high or low we hear
  its frequency.
• Rhythm is a regular time pattern in a series of
  sounds.
• Music is a combination of sound and rhythm that
  we find pleasant.

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24.3 The musical scale

• Most of the music you listen to is created from a
  pattern of frequencies called a musical scale.

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24.3 Music and notes

• Each frequency in the scale is called a note.
• The C major musical scale that starts on the note
  C (262 Hz).

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24.3 Music and harmony

• Harmony is the study of how sounds work together
  to create effects desired by the composer.
• The tense, dramatic sound track of a horror movie
  is a vital part of the audiences experience.
• Harmony is based on the frequency relationships
  of the musical scale.

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24.3 Superposition

• The superposition principle states that when
  sound waves occur at the same time they combine
  to make a complex wave.
• When two frequencies of sound are not exactly
  equal in value, the loudness of the total sound
  seems to oscillate or beat.

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24.3 Music and harmony

• When we hear more than one frequency of sound and
  the combination sounds pleasant, we call it
  consonance.
• When the combination sounds unsettling, we call
  it dissonance.

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24.3 Making sounds

• The human voice is complex sound that starts in
  the larynx, at the top of your windpipe.
• The sound is changed by passing over by
  expandable folds (vocal cords) and through
  openings in the throat and mouth.

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3 MAIN FAMILIES OF INSTRUMENTS

• String instruments
• Wind instruments
• Percussion instruments

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24.3 Making sounds

• For a guitar in standard tuning, the heaviest
  string has a natural frequency of 82 Hz and the
  lightest a frequency of 330 Hz.
• Tightening a string raises its natural frequency
  and loosening lowers it.

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WIND INSTRUMENTS

• 2 types of wind instruments
• Woodwind
• Brass

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WIND INSTRUMENTS

• How wind instruments produce sound a vibration
  is created at one end of its air column, and then
  the vibration creates standing waves in the air
  column.

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PERCUSSION

• How they make sounds They produce sound when
  they are struck

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24.3 Harmonics and music

• The same note sounds different when played on
  different instruments.
• Suppose you compare the note C (262 Hz) played on
  a guitar and the same note played on a piano.
• The variation comes from the harmonics in
  complex sound.
• A single C note from a grand piano might include
  20 or more different harmonics.

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24.3 Harmonics and music

• A tuning fork is a useful tool for tuning an
  instrument because it produces a single frequency