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
an involved psychological process.

Change pitch by altering the vibrating
source.

Response to high pitch usually declines
with age.
2. SOUND INTENSITY AND LOUDNESS


Intensity - refers to pressure variations
Intensity is directly proportional to the
pressure amplitude squared.
2
IA
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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.
Loudness

b = 10 log(I/Io)

Measured in decibels (db)


Loudness depends on our sensitivity to
different frequencies.
Demo – Sound Meter
Common Sound Intensities
Source of Sound
Intensity, I (W/m2) Sound Level, b (db)
Threshold of Hearing
I0 = 10-12
0
Rustle of Leaves
Whisper
10-11
10-10
10
20
Quiet Radio in Home
10-8
40
Conversation in Home
10-6
60
Busy Street Traffic
Riveter
10-5
10-3
70
90
Disco Music Amplified
10-1
110
Air-raid Siren, Nearby
1
120
Jet, 30 m Away
102
140
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.



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.
Harmonics
Next Slide
Fundamental or
First Harmonic
First Overtone or
Second Harmonic
Second Overtone or
Third Harmonic
Closed Organ Pipe
Fundamental or
First Harmonic
First Overtone or
Third Harmonic
Second Overtone or
Fifth Harmonic
Open Organ Pipe
Fundamental or
First Harmonic
First Overtone or
Second Harmonic
Second Overtone or
Third Harmonic

URL - Animated Vibrating String

Demo - Harmonics on a Guitar

Demo - Organ Pipe

URL - Animated Organ Pipe

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.
4. MUSICAL INSTRUMENTS



3 basic types
stringed, air column, and percussion
Because of energy loss, string sections in
orchestras are generally larger.
Electronic
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.

Slide - Fourier Analysis - URL

Slide - Oboe and Clarinet

Slide - Composite Wave

URL – Simultaneous Multiple Harmonics
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