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Musical Sounds Physical Science101 Chapter twenty Amanda Hyer

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Noise

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MusicMusic

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PitchPitch High Low

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Intensity Loudness Soft Loud

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Sound Intensity

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Decibel Sound Level

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ExerciseExercise What is decibel level of a sound that is 1000 times louder than the threshold of human hearing? Given: Intensity/10 -12 =1000=10 3 Wanted: decibel level Solution: dB=10log(Intensity/10 -12 ) dB=10log(10 3 ) = 30 dB

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ExerciseExercise What is decibel level of a sound that is 10,000 times louder than a sound of 50 dB? Given: 50 dB=dB1 and Int2 =10,000 Int1 Wanted: dB2 Solution: Int1=100,000 (10 -12 ) Int2=10,000*100,000 (10 -12 )= 10 9 (10 -12 ) dB2=10log(10 9 ) = 90 dB

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its actually easy intensity 10 (10 1 ) louder 10 dB higher intensity 100 (10 2 ) louder 20 dB higher intensity 1000 (10 3 ) louder 30 dB higher intensity 10,000 (10 4 ) louder 40 dB higher intensity 1,000,000 (10 6 ) louder 60 dB higher

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ExerciseExercise What is decibel level of a sound that is 1000 times louder than a sound of 70 dB? Given: 70 dB=dB1 and Int2 =1000 Int1 Wanted: dB2 Solution: dB2 is 30 dB higher dB2=70+30 dB=100 dB

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Quality The quality of sound from a musical instrument depends on the number of higher harmonics included with the fundamental frequency.

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Quality (a pure tone)

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Quality (1,.4, 0,.2)

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Quality (1, 0, 0,.3, 0, 0,.5)

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Fourier Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1, 0, -(1/9)) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1, 0, -(1/9), 0, +(1/25)) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1, 0, -(1/9), 0, 1/25, 0,-(1/49),0)

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Fourier (1,0) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1,0, (1/3)) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1,0,1/3,0,1/5) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Fourier (1,0,1/3,0,1/5,0,1/7) Any periodic signal can be made up from a sum of harmonic waves (sine waves).

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Compact Discs binary numbers 00 0 01 1 10 2 11 3 100 4=2 2 101 5 10000 16=2 4 11111111 255

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Compact Discs Sample rate of 44,100 bytes per second This gives 0 to 10,000 Hz frequencies

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Reading Assignment! We’ll discuss the chapter by Gregory in your book on Friday of next week.

Reading Assignment! We’ll discuss the chapter by Gregory in your book on Friday of next week.

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