A series of vibrations moving as waves
through air or other gases, liquids, or solids
Our Primary Concern:
Air waves (i.e.,successive compressions and
rarefactions of air )
Sound Waves
Longitudinal:
Whereas light waves are transverse (i.e., the wave is
perpendicular to the direction of travel), sound waves
are longitudinal (i.e., the wave us in the direction of
travel)
Traveling:
The air molecules disturb neighboring molecules,
transferring their energy to them
Sound Waves (cont.)
A Periodic Pressure Wave
Sound Waves (cont.)
A Periodic Pressure Wave
Hearing
The Ear:
The Process:
Sound waves are collected by the auricle
Pressure changes cause the eardrum to vibrate
Vibrations are amplified by the ossicles
Vibrations are transferred to endolymph fluid
in the cochlea
The basilir membrane vibrates at a particular
location
The stereocilia stimulate sensory cells
The resulting electrical impulses are transmitted by the
auditory nerve
Perception of Soundwaves (An Approximation)
Volume:
Difference in amplitude (measured in decibels)
Audible Sounds: 0dB
Painful Sounds: 120dB
Pitch:
Differences in frequency (mesaured in Hz)
Acoustic Signals: 15Hz to 18kHz
Timbre:
Pronounced tam-bur
Includes the waveform's distribution of energy at
different frequencis (i.e., spectra) and
its envelopes/transients (i.e., the attack,
sustain and decay)
Perception of Sound Waves (cont.)
Perception of Sound Waves (cont.)
Localization Defined:
Our ability to locate the origin of a sound
Localization Mechanisms:
The interaural time difference (i.e., the
difference in the time it takes for a sound to reach both
ears). Most people can detect a difference of about 20
microseconds (millionths of a second).
The interaural density difference (i.e., the difference
in amplitude caused by our head interfering with the sound wave).
Frequency filtering performed by the outer ear.
Perception of Sound Waves (cont.)
Complex Wave Forms:
Created when two or more soundwaves travel through
the same medium at the same time
Our Perception:
We can (often) perceive the "original" waves (i.e.,
we perform Fourier analysis)
Biological Basis:
Different locations of the basilir membrane are "tuned"
to different frequencies (except when the tones are close)
Auditory Output Devices
Conventional Loudspeakers:
One or more drivers,
each of which consiste of a diaphragm (often a
semi-flexible cloth or paper with a ... attached) mounted in a
basket
The electrical signal turns an electromagnet on and off,
causing the diaphragm to vibrate, creating pressure
waves
Electrostatic Speakers:
Use a very thin electrically
conductive diaphragm mounted in between two charged panels
Planar Magnetic Speakers:
Use a thin magnetically conductive
diaphragm mounted between two magnetic panels
Rendering
Using a Soundbank:
The synthesizer has a database of sounds
Using Continuous Waveforms:
The synthesizer uses pure waveforms to create complex
waveforms