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Chapter 21 PowerPoint PPT Presentation


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Chapter 21. Musical Sounds. Noise Versus Music. Pitch Loudness Quality . 1. PITCH. The pitch of a sound is related to its frequency. The exact relationship is complex. For simple sounds, the greater the frequency the greater the pitch. For complex sounds, pitch assignment is

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Chapter 21

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Chapter 21 l.jpg

Chapter 21

Musical Sounds


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Noise Versus Music

Pitch

Loudness

Quality


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1. PITCH

  • The pitch of a sound is related to its frequency.

  • The exact relationship is complex.

  • For simple sounds, the greater the frequency

    the greater the pitch.

  • For complex sounds, pitch assignment is

    an involved psychological process.


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  • Change pitch by altering the vibrating source.

  • Response to high pitch usually declines

    with age.


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2. SOUND INTENSITY AND LOUDNESS

  • Intensity -

refers to pressure variations

  • Intensity is directly proportional to the pressure amplitude squared.

  • The human ear can hear intensities over a tremendously large range.

  • Loudness depends on intensity in a complicated way. It does not increase as rapidly as intensity.


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Loudness

  • b = 10 log(I/Io)

  • Measured in decibels (db)

  • Loudness depends on our sensitivity to different frequencies.

  • Demo – Sound Meter


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Common Sound Intensities

Intensity, I (W/m2)

Source of Sound

Sound Level, b (db)

Threshold of Hearing

I0 = 10-12

0

10-11

Rustle of Leaves

10

Whisper

10-10

20

Quiet Radio in Home

10-8

40

10-6

Conversation in Home

60

10-5

70

Busy Street Traffic

10-3

Riveter

90

10-1

Disco Music Amplified

110

1

Air-raid Siren, Nearby

120

102

Jet, 30 m Away

140


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3. QUALITY

  • Quality is the same thing as timbre.

    pronounced TAM-burr (French)

  • It is easy to distinguish two different instruments playing the same note.

  • The quality of a musical sound depends on the number of partial tones and their relative intensities.


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  • The lowest frequency associated with a musical note is called the fundamental frequency.

  • Any partial that is a whole number multiple of the fundamental frequency is called a harmonic.

  • Overtones are consecutively numbered partials of frequency higher than the fundamental.


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Harmonics

Next Slide


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Vibrating String

First Overtone or

Second Harmonic

Second Overtone or

Third Harmonic

Fundamental or

First Harmonic

Closed Organ Pipe

Fundamental or

First Harmonic

Second Overtone or

Fifth Harmonic

First Overtone or

Third Harmonic

Open Organ Pipe

Fundamental or

First Harmonic

Second Overtone or

Third Harmonic

First Overtone or

Second Harmonic


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  • URL - Animated Vibrating String

  • Demo - Harmonics on a Guitar

  • Demo - Organ Pipe

  • URL - Animated Organ Pipe


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  • Demo - Downing’s Resonance Bottle

  • Demo - Speak with different gas in airway

  • Demo - Soda Straw Reed

    and Train Whistle

  • The brain can fill in missing lower harmonics that small speakers cannot create.


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4. MUSICAL INSTRUMENTS

  • 3 basic types

    stringed, air column, and percussion

  • Because of energy loss, string sections in orchestras are generally larger.

  • Electronic


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5. FOURIER ANALYSIS

  • The eardrum responds to a sum of all the waves arriving at a particular instant. Yet the individual sounds are “heard.”

  • Any waveform is composed of an infinite number of simple sine waves of various frequencies and amplitudes.


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  • Slide - Fourier Analysis - URL

  • Slide - Oboe and Clarinet

  • Slide - Composite Wave

  • URL – Simultaneous Multiple Harmonics


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6. COMPACT DISCS

  • Phonograph players give analog signals.

  • Slide - Analog to Digital

  • Digital signal is in binary code.

  • CD has flats and pits and is sampled 44,100 times per second.

  • Slide - Laser Disk


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