Problem 7 Flashcards
Physical definition of sound
Sound is pressure changes in the air
Perceptual definition of sound
Sound is the experience we have when we hear
Condensation
Causes an increase in the density of air molecules
–> increased air pressure
Rarefaction
Decreased density of air molecules
–> decreased air pressure
Pure tone
Occurs when changes in air pressure occur in a sine wave
- -> fundamental building blocks of sound
- -> rare in the environment
Frequency
The number of cycles per second that the pressure changes repeat
–> measured in hertz (Hz)
ex.: 1 Hz = 1 cycle/s
Amplitude
The size of the pressure change
–> difference in pressure between high + low peaks of the sound wave
(dB)
Complex tones
Consist of a number of pure tunes components added together
Harmonics
Refer to the components of complex tones
–> integer multiples of the fundamental
Fundamental/
First harmonic
The lowest frequency that is physically present in the sound
–> lowest tone of the harmonic series (longest WL)
Loudness
The perceptual quality, most closely related to amplitude, of an auditory stimulus
- -> expressed in decibels
- -> depends on amplitude + frequency
Audibility curve
Indicates the threshold for hearing vs frequency
Auditory response area
Area above the audibility curve
–> indicates where we can here sounds
Equal loudness curve
Indicates the sound levels that create the same perception of loudness at different frequencies
Pitch
The perceptual quality we describe as “high” or “low”
- -> associated with music, speech + other natural sounds
- -> can’t be measured in a physical way, but measured by how we perceive it
=> our sense of pitch is limited to those frequencies that create phase locking
(<5.000 Hz)
Tone height
The perceptual experience of increasing pitch that accompanies increases in a tones fundamental frequency
Tone chroma
Notes with the same letter
Effect of the missing fundamental
Describes the constancy of pitch even when the fundamental or other harmonies are removed
Timbre
Describes the quality between 2 tones that have the same
a) loudness
b) pitch
c) duration
but still sound different
ex.: flute + oboes may play the same note but sound different
What influences the differences described in Timbre ?
a) attack
b) decay
Attack
The buildup of sound at the beginning of the tone
–> “fade-in” time
Decay
Decrease in sound at the end of the tone
–> “fade-out” time
Pinnae
Structures that stick out from the sides of the head
Outer ear
Consists of
a) pinnae
b) auditory canal
Auditory canal
Tubelike structure
- -> protects the structures of the middle ear
- -> enhances the intensities of some sounds
Middle ear
Small cavity that separates the outer + inner ears
–> contains the ossicles
Ossicles
3 smallest bones in the body, that make up the middle ear
a) malleus
b) incus
c) stapes
Tympanic membrane/
Eardrum
Located between the outer + middle ear
Middle Ear muscles
Smallest skelletal muscles that are attached to the ossicles
–> at very high sound levels they contract to dampen the ossicles vibration
ex.: contract so that sounds from chewing won’t interfere with the perception of speech from other people
Cochlea
Snail like structure
- -> main structure of the inner ear
- -> performs fourier analysis (Tonotopy)
Scala vestibuli
Upper half of the cochlea
Scala tympani
Lower half of the cochlea
Cochlear partition
Separates the 2 scalas
Organ of corti
Located between the 2 scalas of the cochlea
–> contains
a) basilar membrane
b) tectorial membrane
c) hair cells –> receptors for hearing
Cilia
Thin processes extending from the tops of the hair cells
–> bend in response to pressure changes
Phase locking
The property of firing at the same place in the sound stimulus
- -> refractory period
- -> only occurs at frequencies below 5.000 Hz
Temporal coding
Groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analyzed
Place theory of hearing
The frequency of a sound is indicated by the place along the cochlea at which nerve firing is highest
–> each place on the basil membrane is tuned to respond best to a different frequency
Cochlear implant
Used to create hearing in people with deafness caused by damage to the hair cells in the chochlea
–> consists of
a) microphone
b) sound processor
c) transmitter
- -> sends signals to the electrodes implanted along the cochlea
Cochlear amplifier
Outer hair cells expand + contract in response to the vibration of the basilar membrane
–> this action amplifies/sharpens vibration on the basilar membrane
–> basilar membrane vibrates to each harmonic
How are pressure changes changed into electricity ?
- Sound waves reach the tympanic membrane + set it into vibration
- Consequently the following structures are set into vibration
a) Malleus
b) Incus
c) Stapes
- Stapes transmits the virbrations to inner ear by pushing on the membrane covering the oval window
- This movement of the stapes, sets cochlea into vibration
- Back + forth motion of oval window transmits the vibrations to the liquid inside of the cochlea
- Basil membrane is set into motion
- Organ of corti is set into an up + down motion
- -> tectorial membrane is moved back and forth - Cilia bend, because they are in contact with tectorial m.
- Cilias movement to the right causes the tip links to stretch which opens ion channels
- Na+ ions flow into cell
- Bending in other direction closes channels
- -> back + forth bending causes alternating bursts od electrical signals
Which density problem occurs in the ear ?
Inner ear contains a watery liquid
- -> water is more dense
- -> vibrations that would be directly passed from the air into liquid wouldn’t reach its destination
How do the ossicles resolve the density problem ?
a) by being hinged
- -> lever action
b) by concentrating the vibration on stapes which increases the pressure
Hearing range
–> one can hear sounds between 20 Hz - 20.000 Hz
–> one is most sensitive to sounds betw. 2.000 - 4.500 Hz (Speaking range)
Fourier analysis
The analysis of a periodic function into its simple sinusoidal or harmonic components
Auditory masking
Refers to one sound covering or masking another - making it virtually impossible to hear the sound being masked
–> effect is strongest for high frequencies
