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Chapter 21

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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  1. Chapter 21 Musical Sounds

  2. Noise Versus Music Pitch Loudness Quality

  3. 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.

  4. Change pitch by altering the vibrating source. • Response to high pitch usually declines with age.

  5. 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.

  6. Loudness • b = 10 log(I/Io) • Measured in decibels (db) • Loudness depends on our sensitivity to different frequencies. • Demo – Sound Meter

  7. 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

  8. 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.

  9. 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.

  10. Harmonics Next Slide

  11. 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

  12. URL - Animated Vibrating String • Demo - Harmonics on a Guitar • Demo - Organ Pipe • URL - Animated Organ Pipe

  13. 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.

  14. 4. MUSICAL INSTRUMENTS • 3 basic types stringed, air column, and percussion • Because of energy loss, string sections in orchestras are generally larger. • Electronic

  15. 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.

  16. Slide - Fourier Analysis - URL • Slide - Oboe and Clarinet • Slide - Composite Wave • URL – Simultaneous Multiple Harmonics

  17. 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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