Chapter 21Chapter 21Chapter 21Chapter 21

Musical SoundsMusical Sounds

Noise Versus MusicNoise Versus Music

PitchPitch

LoudnessLoudness

Quality Quality

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. PITCH1. PITCH1. PITCH1. PITCH

Response to high pitch usually declines

with age.

Change pitch by altering the vibrating source.

2. SOUND INTENSITY AND LOUDNESS2. 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.

2I A

LoudnessLoudness

= 10 log(I/Io)

Measured in decibels (db)

Loudness depends on our sensitivity to different frequencies.

Demo – Sound MeterDemo – Sound Meter

Common Sound IntensitiesCommon Sound Intensities

Source of SoundSource of Sound Intensity, I (W/mIntensity, I (W/m22))Sound Level, Sound Level, (db) (db)

Threshold of Hearing I0 = 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

102

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

3. QUALITY3. QUALITY3. QUALITY3. 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 Harmonics

Next SlideNext Slide

First Overtone orThird Harmonic

Fundamental orFirst Harmonic

Second Overtone orFifth Harmonic

Fundamental orFirst Harmonic

First Overtone or

Second Harmonic

Second Overtone orThird Harmonic

Fundamental orFirst Harmonic

First Overtone orSecond Harmonic

Second Overtone orThird Harmonic

Closed Organ Pipe

Open Organ Pipe

URL - Animated Vibrating StringURL - Animated Vibrating String

Demo - Harmonics on a GuitarDemo - Harmonics on a Guitar

Demo - Organ PipeDemo - Organ Pipe

URL - Animated Organ PipeURL - Animated Organ Pipe

Demo - Downing’s Resonance BottleDemo - Downing’s Resonance Bottle

Demo - Speak with different gas in airwayDemo - Speak with different gas in airway

Demo - Soda Straw Reed Demo - Soda Straw Reed

and Train Whistleand Train Whistle

The brain can fill in missing lower

harmonics that small speakers cannot

create.

4. MUSICAL INSTRUMENTS4. MUSICAL INSTRUMENTS4. MUSICAL INSTRUMENTS4. MUSICAL INSTRUMENTS

3 basic typesstringed, air column, and percussion

Because of energy loss, string sections in orchestras are generally larger.

Electronic

5. FOURIER ANALYSIS5. FOURIER ANALYSIS5. FOURIER ANALYSIS5. 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 - URLSlide - Fourier Analysis - URL

Slide - Oboe and ClarinetSlide - Oboe and Clarinet

Slide - Composite WaveSlide - Composite Wave

URL – Simultaneous Multiple URL – Simultaneous Multiple

Harmonics Harmonics

6. COMPACT DISCS6. COMPACT DISCS

Phonograph players give analog signals.Phonograph players give analog signals.

Slide - Analog to DigitalSlide - Analog to Digital

Digital signal is in binary code.Digital signal is in binary code.

CD has flats and pits and is sampled CD has flats and pits and is sampled

44,100 times per second.44,100 times per second.

Slide - Laser DiskSlide - Laser Disk