Loudness and Pitch

perceptual definition of sound

the experience we have when we hear

physical definition of sound

pressure changes in the air or other medium

pure tone

a tone with a single frequency of vibration

amplitude

Height of a wave

frequency

the number of complete wavelengths that pass a point in a given time

characteristics of complex sounds

all sound waves can be described as some combination of sine waves, natural sounds consist of a fundamental frequency superimposed by additional waveforms with higher frequencies (harmonics)

pinnae

external ears

auditory canal

3cm tube-like structure protects middle ear

tympanic membrane

Cone-shaped membrane separates outer and middle ear

Sound waves induce pressure difference on either side, causing it to vibrate

middle ear

2 cubic cm cavity containing ossicles (smalles bones in the human body)

ossicles

malleus, incus, stapes

amplify vibrations of tympanic membrane and transmit them to the inner ear at the oval window

parts of the inner ear

cochlea, vestibule, semicircular canals

cochlea

snail-like liquid-filled organ, vibration of oval window displaces fluid changing pressure which propagates up and down spiral structure

Cochlea consists of three parallel canals (vestibular, middle, tympanic)

Auditory transduction triggered by movement of basilar membrane, separates middle and tympanic canals

Auditory transduction

Motion of basilar membrane translated into neural signals by structures in Organ of Corti which extends across its surface

Voltage generated when extremely sensitive specialised hair cells in the OOC are bent

Produces impulses in auditory nerve cells, sent to the brain

dangers of loud sounds

How many possible orders for full counterbalancing are there in a study with four conditions?

how is loudness perceived

amplitude of sounds waves

how is sound levels measured

in decibels

logarithmic scale

change of 20db = ten fold increase

rate code

sounds amplitude coded in the firing rate of auditory nerve fibres

spontaneous rate

some fibres have high spontaneous rate and saturate rapidly, others have low spontaneous rates and saturate slowly

does loudness depend on frequency?

yes - auditory systems are not equally sensitive to all sound frequencies

how do we perceive pitch?

depends on frequencies - humans are sensitive to a wide range

place code

sound frequencies cause vibration in specific areas along the basilar membrane

low - near apex

high - near base

timing code

frequency not only signalled by which auditory nerve fibres respond, but also when they respond

phase locking

auditory nerve responses synchronised to changes in pressure, up to frequencies of about 4000 Hz

how is pitch determined

by fundamental frequency of a sound - number, frequency ratios, and relative amplitudes of the harmonics dictates the quality / timbre of the sound

missing fundamental illusion

Removing the 1st harmonic doesn't change pitch of a periodic complex tone