Transcript Chapter 21 Musical Sounds

Chapter 21
Musical Sounds
1. NOISE VERSUS MUSIC
Wham - Noise and Wave Forms
Three characteristics of a musical tone:
Pitch
Loudness
Quality
2. PITCH
The pitch of a sound relates 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.
3. SOUND INTENSITY AND LOUDNESS
Intensity - refers to pressure variations
Intensity is directly proportional to the
pressure amplitude squared.
I  A2
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)
A difference of 10 dB corresponds to a ratio of
intensities of 10X.
Loudness depends on our sensitivity to
different frequencies.
Common Sound Intensities
2
Source of Sound
Intensity (W/m )
Jet 30 m away
10
Air-raid siren, nearby
1
Disco music, amplified
10
-1
110
Riveter
10
-3
90
Busy street traffic
10
-5
70
Conversation in home
10
-6
60
Quiet radio in home
10
-8
40
Whisper
10
-10
20
Rustle of leaves
10
-11
10
Threshold of hearing
10
-12
0
2
Sound Level (db)
140
120
Response of the Ear at
Constant Loudness
4. QUALITY
Quality is the same thing as timbre.
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.
Same Note - Different Instrument
Human Voice
Harmonics and Overtones
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.
Adding Harmonics
1st
2nd
Sum
Demo - Harmonics on a Guitar
Demo - Organ Pipe
Speaker Shortcomings
The brain can fill in missing lower
harmonics that small speakers cannot
create.
5. MUSICAL INSTRUMENTS
Three basic types
 stringed, air column, and percussion
Because of energy loss, string sections in
orchestras are generally larger.
Electronic
6. 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.
Adding Harmonics
Spreadsheet
7. COMPACT DISCS
Phonograph players give analog signals.
Digital signal is in binary code.
CD has flats and pits and is sampled 44,100 times
per second.
Diatonic C Major Scale
Letter
Note Name
Frequency
(Hz)
do
C
264
re
D
297
mi
E
330
fa
F
352
sol
G
396
la
A
440
ti
B
495
do
C
528
Frequency
ratio
Interval
9/8
Whole
10/9
Whole
16/15
Half
9/8
Whole
10/9
Whole
9/8
Whole
16/15
Half
Chapter 21 Review Questions
The quality of a musical note can be changed
by simply playing the note on a different
instrument.
(a) True
(b) False
If the note middle C has a pitch of 262
vibrations per second, its second overtone on
a vibrating string has a frequency of
(a) 131 vibrations per second
(b) 262 vibrations per second
(c) 524 vibrations per second
(d) 786 vibrations per second
(e) none of the above
The three characteristics of a musical tone are
loudness, quality, and timbre.
(a) True
(b) False
The wavelength of the fundamental vibration
on a l m long string is half as long as the
wavelength of the fundamental vibration in a
closed organ pipe of l m length.
(a) True
(b) False
The ear can “Fourier analyze” a sound wave,
but the eye cannot “Fourier analyze” a light
wave.
(a) True
(b) False
If the fundamental frequency of a violin string
is 440 Hz, what is the frequency in Hz of the
first overtone?
(a) 1320
(b) 880
(c) 440