The parts of the middle ear, Audio range, Sound localization, Loudness perception

Outer ear is called

Pinna/Auricle

Pinna 3 main parts

• tragus

• helix

• lobule

Middle ear - Ear canal

funnels sound waves to the ear drum/middle

Strong resonances between 2 kHz - 4 kHz,

Speech is largely derived from consonants, is in this range

Ear drum

tympanic membrane

• attached to ear canal and middle ear bones

• responds to changes in sound pressure → vibrates acorrdingly

• acoustic energy becomes mechanical

Middle ear has the

3 smallest bones in the human body

Middle ear bones are

• malleus, incus, stapes

• also hammer, anvil, stirrup

ossicles are the

3 bones of middle ear

ossicles transfer

sound vibration from ear drum → oval window

• amplify sound coming from tympanic membrane

oval window

transfers sound energy to cochlea

inner ear contains

cochlea, semi circular canals

cochlea is full of

fluid that vibrates

• based on acoustical energy from middle ear

• membrane is lined with cillia, they move and send signals to brain

auditory nerve

carries electrical signals from cochlea to brain

bone conduction

• conduction of sound to inner ear through bones of skull

• sound can be perceived even if ear canal blocked

3 main mechanisms our auditory system can use

1. sound intensity differences

2. temporal differences

3. spectral differences

sound localization

relationship between actual position of sound source and perceived location of that “auditory event”

sound localization is measured in

localization blur

ITD: Inter-aural time differences

• difference in time of arrival of sound between 2 ears

ILD: Inter-aural level differences

• head acts as a physical sound barrier for those wavelengths above 1.6 kHz

• difference in sound pressure between two ears allows brain to locate sound source

vertical plane

sound reaches both ears at same time

• less precise in humans

ITD and ILD are only on

horizontal plane

intensity

amount of energy striking an area

• measured in watts per square meter

• watts/m2

sound intensity

• power carried by sound waves per unit area

Sound intensity is meaured in Decibels (dB)

• objective measure of sound

• is a relative unit of measure

sound is a

pressure wave

Loudness perception is

frequency dependent

A Weighting

• reflects (human) reduced sensitivity to lower frequencies/higher frequencies

• most common type used in noise measurement

C Weighting

• objective

• for loud sounds over 100dB, where ear’s response is more linear

auditory masking

• two frequencies occur simultaneously

• amplitude of one masks the other

Temporary Threshold Shift (TTS)

• caused by exposure to loud noise/drugs

• fatigues ears, no permanent damage

Permanent Threshold Shift (PTS)

• hearing damanged from extended exposure to loud noise, trauma, illness, age

• non-recoverable

Acoustic Reflex

• involuntary muscle contract in middle ear

• in response to loud sound

• decreases transmission of energy

NIOSH and OSHA

• niosh better

• niosh has stricter requirements

• both are not perfect - reflect steady-state sound

cocktail party effect

• brain can focus on one thing to listen to

• works best as binaural (2 ears)

Missing Fundamentals

• when enough overtones are present in a complex tone, auditory assigns it a pitch, filling in missing fundamental

Mics are

transducers (turn SP into V)

Dynamic Mic

• Diaphragm hit by sound waves

• energy makes coil move

• causes changes in magnetic field

• Creates changes in V (analagous to SP)

Conductive Mic

• diaphragm separated from back by air

• current applied, charges air gap

• Sound waves move diaphram

• causes changes in V

• Requires power supply, usually “phantom power” from mixer

Dynamic used for

live events

condenser used for

studio

directivity

How sensitive mics are to sound coming from various directions

polar patterns

show mic directivity

Omnidirectional

equal sensitivity from all direct

cardioid

shaped like heart, reject sound from behind, most common (especially for live)

Bi-directional

Figure 8, blocks sides, picks up front and back

small diaphragm

13mm

more linear freq

superior transient response

typically front address

large diaphragm

>25mm

more color

typically side address

lavalier

ultra small

discreet

attatched to clothes or skin

close/spot micing

1cm to 1m

placed in direct field

relatively absent of rooms acoustic signature

exaggerated dynamics

main/distant micing

1-5m

placed around “critical distance” (equal amt of sound direct and reflected)

normal dynamics

strong acoustic signature

Room micing

>5m

placed in reverberant field

dominates tone color

acoustic signature only

reduced dynamics feel