loudness & pitch

Question 1

what are Pure tones

Answer 1

sounds where pressure changes follow a sine wave and can be described by their amplitude and frequency
- occurs when changes in air pressure form a perfect sinusoidal wave

Question 2

define sound

Answer 2

physical stimulus out in the world

- sound is pressure changes in the air or other medium caused by the vibration of an object

Question 3

complex sounds are made up of…

Answer 3

2 or more waveforms with different frequencies

Question 4

naturally produced sounds are…

Answer 4

typically made up of a fundamental frequency and several harmonics

Question 5

amplitude

Answer 5

= how much air pressure varies

• size of the variation in air pressure
• related to perception and loudness

greater amplitude = wavelengths increase in height

Question 6

frequency

Answer 6

= number of cycles per second
- related to perception of pitch

greater frequency = wavelengths get closer together

Question 7

all sound waves can be described as a combination of..

Answer 7

sine waves

Question 8

natural sound often consist of a..

Answer 8

fundamental frequency superimposed by additional waveforms with higher frequencies (the harmonics)

Question 9

The outer ear

Answer 9

1. Pinnae 
function = capture sound waves and project to AC

2. Auditory canal
function = protects middle ear

3. Tympanic membrane (eardrum)
   - cone shaped separating the outer and middle ear

Question 10

middle ear

Answer 10

contains ossicles (3 smallest bones)

• Malleus (hammer)
• Incus (anvil)
• Stapes (stirrup)
• the bones amplify the vibrations of the tympanic membrane and transmit them to the inner ear at the oval window

Question 11

inner ear

Answer 11

cochlea:

• liquid filled
• consists of 3 parallel canals (vestibular, middle and tympanic)
• vibration of the oval window displaces fluid in the cochlea, resulting in a change in pressure which propagates up and down the spiral structure
• auditory transduction is triggered by motion of the basilar membrane, which separates the middle and tympanic canals

Question 12

auditory transduction

Answer 12

Motion of the basilar membrane are translated into neural signals by structures in the organ of corti

• a voltage is generated when specialised hair cells contained within the organ corti are bent
• this produces impulses in auditory nerve cells which are sent to the brain, transmitted via auditory nerve fibres

Question 13

perception of loudness is related to the amplitude of sound waves

Answer 13

• the range of sound amplitudes encountered is very large

- measured on a logarithmic scale in units called decibels

Question 14

rate code

Answer 14

sound amplitude is coded in the firing rate of auditory nerve fibres.
- the higher the amplitude, the more response your gonna get in cells

• some fibres have high spontaneous rates and saturate rapidly, while others have low spontaneous rates and saturate slowly which enables us to discriminate loudness across a range of sound levels.

Question 15

perceived loudness is not directly proportional to amplitude

Answer 15

• for a second to double in loudness, it needs to be more than doubled in amplitude
• sounds with the same amplitude but different frequencies will differ in loudness

Question 16

what happens to pitch when you have a higher frequency

Answer 16

• higher pitch

Question 17

what is the range of frequency humans can hear

Answer 17

20Hz - 20,000Hz (20kHz)

Question 18

sound frequency is coded by the auditory system in 2 ways:

Answer 18

1. Place code - sounds of given frequency cause vibrations in specific areas along the basilar membrane (low = near apex, high = near base)
2. timing code - auditory nerve responses are phase-locked to pressure changes in sounds up to around 4000Hz

Question 19

experiments using electrical stimulation via cochlea implants suggest …

Answer 19

that both the place and timing of stimulation affect the perception of pitch

Question 20

pitch is typically determined by ..

Answer 20

the fundamental frequency (lowest) of sound

Question 21

define timbre

Answer 21

characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness

• The number, frequency ratios and relative amplitudes of the harmonics dictates the quality or timbre of sound