Transcript Chapter 6: The Human Ear and Voice

Chapter 6: The Human Ear and Voice
The study of the human ear and the process by which
sound waves are received and transmitted to the nerve
endings that convert mechanical vibrations into electrical
impulses.
Our study will relate the basic anatomy of the peripheral
auditory system to the important features of the place
theory of hearing.
The frequency and amplitude responses of the ear.
Vocal system and the production of speech and musical
sounds.
Analysis of speech patterns.
Peripheral Auditory System
The human ear is one of the most amazing organs of the
body.
Possesses an incredible range of sensitivity in frequency
and amplitude responses.
Frequency response: 20 Hz  20 kHz.
A factor of about 1000 or ten octaves
Amplitude/Intensity response: Pressure variations of
about 1,000,000 to 1.
Intensity variations from 10-12 W/m2 – 1 W/m2.
Peripheral
Auditory
System
Three Parts:
Inner ear
Middle ear
Outer ear
Function of the
Outer Ear
Eardrum
Middle Ear
Consists primarily of the bone chain of the three ossicles: the hammer, the
anvil, and the stirrup.
These bones amplify the vibrations coming from the eardrum and transmit to
the fluid of the inner ear.
Muscles attached to the ossicles help to limit the vibrations of very largeamplitude continuous sounds.
Sharp noises such as gunshots or loud music may occur too quickly for the
protective mechanism to prevent damage to the middle ear.
Cochlea
Oval and
Round
Window
The organ of Corti
Inner Ear and Balance
Inside the inner ear are three semicircular canals. Each canal
contains tiny hairs, crystals, and fluid. These structures help the
canals sense up-and-down, forward and backward, and side-toside motion. Nerves carry the signals from the canals to the brain.
Place Theory of Hearing
The place theory hearing correlates frequency with location
of the response along the basilar membrane.
Place theory of hearing
Place theory of hearing states that our perception of
sound depends on where each component frequency
produces vibrations along the basilar membrane.
Therefore, the pitch of a pure tone would be determined
by where the membrane vibrates. In technical terms, it
states that frequency is encoded according to the
tonotopic organization of the neurons.
Place theory competes with the rate theory of hearing,
which instead states that pitch is signaled by the rate at
which the neurons fire.
Pitch sharpening
The relative shortness of the basilar membrane
contrasts with the large number of pitches which
people can distinguish. Place theory is generally
seen as incomplete, lacking a mechanism which
would explain our large pitch resolution. Research
using modern cochlear implants suggests that the
perception of pitch may depend on both the
neurons' location and rate at which they fire.
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/place.html
Anatomy of the Ear
Sound enters the ear, travels through the auditory canal,
and reaches the eardrum. The auditory canal is
approximately a tube open at only one end. The other end
is closed by the eardrum. A typical length for the auditory
canal in an adult is about 3 cm. The speed of sound is 343
m/s. What is the fundamental frequency of the canal?
(Interestingly, the fundamental frequency is in the
frequency range where human hearing is most sensitive.)
Amplitude Response of the Ear
Human Ear and Sensitivity
Audible frequency range: 20 Hz – 20,000 Hz
Audible intensity range: 10–12 W/m2 - 1 w/m2
10–12 W/m2 = Threshold of hearing
1 W/m2 = Threshold of pain
Decibels
The decibel (dB) is a measurement unit used when comparing
two sound intensities.
The intensity level b (expressed in decibels) relative to the
threshold of hearing, Io is defined as follows:
Typical Sound Intensities and Intensity Levels Relative to
Intensity Level b
the Threshold of Hearing Intensity I
(W/m2)
(dB)
Threshold of hearing
1.0 × 10-12
0
Rustling leaves
1.0 × 10-11
10
Whisper
1.0 × 10-10
20
Normal conversation
(1 meter)
3.2 × 10-6
65
Inside car in city traffic
1.0 × 10-4
80
Car without muffler
1.0 × 10-2
100
Live rock concert
1
120
Threshold of pain
1
120
Periodicity
If two or more tones whose frequencies are successive
harmonics in some overtone series sounded
simultaneously, an additional frequency will be “heard” by
most listeners, particularly trained musicians.
Periodicity:
The neural mechanism of the ear is able to identify the two
frequencies as being members of an overtone series and
assigns to the total stimulus the fundamental frequency.
This is called periodicity pitch, missing fundamental, or
subjective fundamental.
Fundamental Tracking
If one plays a sequence of pairs of tones that have
frequency ratio 3 to 2 but have different
fundamental frequencies, the ear will recognize
the periodicity of each pair of notes and supply the
fundamental tone for each. This is called
fundamental tracking.
Eg: 200 and 300 Hz followed by 300 and 450 Hz.
Fundamental tracking is used in the production of
very-low-frequency organ tones by sounding the
2nd and 3rd harmonics together.