CH. 21 Musical Sounds. Musical Tones have three main characteristics 1)Pitch 2) Loudness 3)Quality.
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Transcript of CH. 21 Musical Sounds. Musical Tones have three main characteristics 1)Pitch 2) Loudness 3)Quality.
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CH. 21 Musical Sounds
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Musical Tones have three main characteristics
1) Pitch
2) Loudness
3) Quality
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• Pitch-Relates to frequency. In musical sounds, the
sound wave is composed of many different frequencies, so the pitch refers to the lowest frequency component.
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• Slow Vibrations = Low Frequency.
• Fast Vibrations = High Frequency.
• Ex: Concert A = 440 vibrations per second.
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• Intensity: Depends on the Amplitude.
• Intensity is proportional to the square of the amplitude.
• In symbols: I A2
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• Intensity is measured in units of Watts/m2.
(i.e. power per unit area)
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• Another closely related quantity is the intensity level, or sound level.
• Sound level is measured in decibels. (dB)
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• The decibel scale is based on the log function.
# dB =10 log(I/Io)
where Io = some reference intensity, such as the threshold of human hearing - (Io = 10-12 Watts/ m2)
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• Examples:• Source of Intensity Sound
SoundLevel
• Jet airplane 102 140
• Disco Music 10-1 110
• Busy street
traffic 10-5 70
• Whisper 10-10 20
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• Loudness: Physiological sensation of sound detection.
• The ear senses some frequencies better than others.
• Ex: A 3500Hz sound at 80 dB sounds about twice as loud as a 125-Hz sound at 80dB.
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• Quality: A piano and a clarinet can both play the note “middle C”, but we can distinguish between them.
Why? - Because the quality of the sound is different.
•The quality is also called the “Timbre”.
The number and relative loudness of the partial tones determines the “Quality” of the sound.
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Musical sounds are composed of the superposition of many tones
which differ in frequency.• The various tones are called
partial tones.
• The partial tone with the lowest frequency is called the fundamental frequency.
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Fundamental or 1st harmonic
2nd harmonic
3rd harmonic
NODE
Antinode
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L
L = /2
L = L
Fundamental or 1st harmonic
2nd harmonic
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Finding the nth harmonic
(2L/2) f2= (2L) f1
f2 = 2f1 ------> fn = nf1
L = n/2 -----> n= 2L/n
where (n = 1,2,3,4,…)
v = 1f1 v = 2f2
2f2 = 1f1
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Musical Instruments Scale&Octave
• The tone an octave above has twice the frequency as the original tone.
Scale: A succession of notes of frequencies that are in simple ratios to one another.
•Octave: The eighth full tone (or 12th successive note in a scale) above or below a given tone.
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1 2 3 4 5 6 7 8
1 2 3 4 5
Whole Tones
Half Tones
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• We can decompose a given waveform into its individual partials by Fourier Analysis.
•Musical sounds are composed of a fundamental plus various partials or overtones.
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• Joseph Fourier, in 1822, discovered that a complicated periodic wave could be constructed by simple sinusoidal waves, and likewise deconstructed into simple sinusoidal waves.
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• The decomposition of a complicated waveform into simpler sinusoidal waveforms is known as Fourier Analysis
•The construction of a complicated waveform from simpler sinusoidal waveforms is known as Fourier Synthesis.
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-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 1 2 3 4 5 6 7 8
2/[sin(x)+1/3sin(3x)+1/5sin(5x)]
Example of Fourier Synthesis
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COMPACT DISC
• Digital Audio
Howstuffworks "How Analog-Digital Recording Works"
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t1 t2 t3
Analogue Signal
Digital Signal
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End of Chapter 20