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Published byHorace Harrell Modified over 9 years ago
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Chapter 21 Musical Sounds
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Noise Versus Music Pitch Pitch Loudness Loudness Quality Quality
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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. 1. PITCH
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Response to high pitch usually declines with age. Change pitch by altering the vibrating source.
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2. SOUND INTENSITY AND LOUDNESS Intensity - refers to pressure variations 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. Intensity is directly proportional to the pressure amplitude squared.
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Loudness = 10 log(I/I o ) Measured in decibels (db) Loudness depends on our sensitivity to different frequencies. Demo – Sound Meter
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Common Sound Intensities Source of Sound Intensity, I (W/m 2 ) Sound Level, (db) Threshold of HearingI 0 = 10 -12 0 10 20 40 60 70 90 110 120 140 10 -11 10 -10 10 -8 10 -6 10 -5 10 -3 10 -1 1 10 2 Rustle of Leaves Whisper Quiet Radio in Home Conversation in Home Busy Street Traffic Riveter Disco Music Amplified Air-raid Siren, Nearby Jet, 30 m Away
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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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First Overtone or Third Harmonic Fundamental or First Harmonic Second Overtone or Fifth Harmonic Fundamental or First Harmonic First Overtone or Second Harmonic Second Overtone or Third Harmonic Fundamental or First Harmonic First Overtone or Second Harmonic Second Overtone or Third Harmonic Vibrating String Closed Organ Pipe Open Organ Pipe
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URL - Animated Vibrating String URL Demo - Harmonics on a Guitar Demo - Organ Pipe URL - Animated Organ Pipe URL
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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 URL Slide - Oboe and Clarinet Slide - Composite Wave URL – Simultaneous Multiple Harmonics URL
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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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