Hearing

Question 1

What is sound?

Answer 1

A CHANGE in pressure propagated through an elastic medium (elastic is usually air).
- Very small changes of a large steady pressure

Question 2

The magnitude of standard atmospheric pressure is
a) enormous
b) tiny
in relationship to the magnitude of the pressure changes that normal sounds produce

Answer 2

a) enormous

Question 3

The auditory system has evolved to….

Answer 3

Detect just small changes of huge steady maintained atmospheric pressure

Question 4

What is a sound in terms of waves?

Answer 4

A sound is a wave of mechanical disturbance that move away from the sound source slowly.

Question 5

What is the speed of sound?

Answer 5

340m/sec

Question 6

What is the speed of light in terms of its wave of electromagnetic radiation and it’s relationship to sound?

Answer 6

300,000km/sec, 1 mil times faster than sound

Question 7

What is the measure of pressure?

Answer 7

force per unit area, units are pascals or micropascals

Question 8

How do you measure amplitude of sound (extent of change on a sound level meter)

Answer 8

running standard deviation of pressure changes - strictly a root mean square (rms) of pressure changes, and displays the answer

Question 9

What is the threshold of human hearing for a 1000Hz tone? (pure tone)

Answer 9

20 micropascals (uPa)

Question 10

What is the threshold of auditory pain?

Answer 10

100,000,000 micropascals

Question 11

To compress the range of numbers needed to express sound level, what scale is used?

Answer 11

A logarithmic scale

Question 12

What has been done to standardise the logarithmic scale to express sound?

Answer 12

It has been agreed to refer all pressure change measurements to the pressure change corresponding to the physical magnitude of pressure changes at the threshold for human hearing of a 1000Hz (20uPa) pure tone
- Consequently, measures of sound amplitude tell you how much larger the sound is than the pressure change that an average human can just hear at 1000Hz

Question 13

What is the units of measurement for amplitude?

Answer 13

decibels (dB)

Question 14

Equations for sound pressure level

Answer 14

20*log(pressure measured / reference pressure)

• when reference pressure is 20uPa and the answer is in dB

Question 15

True or false?

Because log is used in the SPL equation, doubling the pressure always corresponds to a constant increase in dBs

Answer 15

True

e.g. 2 increasing by 2 = the same change in dB as 4 increasing by 4

Question 16

Zero decibels means?

Answer 16

Humans can’t or can barely hear it (some animals are more sensitive)

Question 17

In that reading all the sound frequencies between 20 and 20,000 Hz are weighted equally why is this not appropriate for psychologists?

Answer 17

Because the measured amplitude of the pressure changes over time in the room includes very low and high frequency components outside the range of human hearing.

Question 18

How can a more psychologically relevant measure of sound intensity be obtained?

Answer 18

By filtering the sounds according to the relative sensitivity of human hearing.

• Adjusting the SLM to scale or filter various frequencies according to characteristics of average human hearing
• Downgrading the contribution of very low and high frequency stimuli as sensitivity to these are poor

Question 19

What are measures of sound amplitude made using this human sensitivity weighting function called?

Answer 19

dB(A) measures.

Question 20

What does the huge differences between dB SPL and dB(A) measures imply?

Answer 20

That there is a great deal of energy in the classroom in frequency bands which are unimportant for human perception.

Question 21

Filtering

Answer 21

Excluding some frequencies and passing others

Question 22

What frequencies does the ear exclude

Answer 22

under 20Hz and over 20,000Hz (may be present but d not affect the auditory system)

Question 23

What is a filter function?

Answer 23

The response of a single auditory neuron (coming from the cochlea) to sound stimuli of various frequencies

Question 24

True or false?

If the auditory system is damaged or dysfunctional the band of frequencies becomes much wider?

Answer 24

Trie

Question 25

What is the restricted band of frequencies around the test tone which is important for your detection of that test tone called?

Answer 25

Critical band, at 2000Hz and is about 300Hz wide

Question 26

What exactly is lost during hearing loss and what do test find on these people?

Answer 26

Loss of receptor hair cells.

Broader critical bands

Question 27

auditory masking

Answer 27

Reduced audibility of a sound signal when in the presence of a second signal of higher intensity within the same critical band

Question 28

Leaving away from industrialised areas suggests more or less hearing loss?

Answer 28

Less hearing loss (Easter Islanders)

Question 29

In typical hearing loss other than the sound becoming weaker what else happens?

Answer 29

Major changes in how the sounds are processed.

Causing distortions and hampers speech comprehension

Question 30

What is a voltage that varies overtime called?

Answer 30

A waveform

Question 31

What is a waveform of a pure tone called?

Answer 31

A sine wave

Question 32

How is a complex waveform related to simple sine waves?

Answer 32

a complex waveform can be broken down into simple sine waves or built up from them (via addition)

Question 33

What is the frequency of a waveform with 4 msec between peaks?

Answer 33

250Hz

Question 34

What is the quality of sound called?

Answer 34

Timbre

Question 35

How large a difference in frequency was needed for you to detect a difference between that (variable frequency) test tone and a 500Hz tone?

Answer 35

Under optimal conditions (not true here) good observers can detect the difference between 500 and 502 Hz , just 2 Hz

Question 36

Low-pass filtering a stimulus removes what frequencies…..?

Answer 36

Low pass filtering removes high frequencies (“passes” the low frequencies)
7. sounds become what you might describe as muffled

Question 37

Low-pass filtering of speech has the same effect. Which group of people would experience such low-pass filtered speech….?

Answer 37

old people