Hearing Flashcards
What is sound?
A CHANGE in pressure propagated through an elastic medium (elastic is usually air).
- Very small changes of a large steady pressure
The magnitude of standard atmospheric pressure is
a) enormous
b) tiny
in relationship to the magnitude of the pressure changes that normal sounds produce
a) enormous
The auditory system has evolved to….
Detect just small changes of huge steady maintained atmospheric pressure
What is a sound in terms of waves?
A sound is a wave of mechanical disturbance that move away from the sound source slowly.
What is the speed of sound?
340m/sec
What is the speed of light in terms of its wave of electromagnetic radiation and it’s relationship to sound?
300,000km/sec, 1 mil times faster than sound
What is the measure of pressure?
force per unit area, units are pascals or micropascals
How do you measure amplitude of sound (extent of change on a sound level meter)
running standard deviation of pressure changes - strictly a root mean square (rms) of pressure changes, and displays the answer
What is the threshold of human hearing for a 1000Hz tone? (pure tone)
20 micropascals (uPa)
What is the threshold of auditory pain?
100,000,000 micropascals
To compress the range of numbers needed to express sound level, what scale is used?
A logarithmic scale
What has been done to standardise the logarithmic scale to express sound?
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
What is the units of measurement for amplitude?
decibels (dB)
Equations for sound pressure level
20*log(pressure measured / reference pressure)
- when reference pressure is 20uPa and the answer is in dB
True or false?
Because log is used in the SPL equation, doubling the pressure always corresponds to a constant increase in dBs
True
e.g. 2 increasing by 2 = the same change in dB as 4 increasing by 4
Zero decibels means?
Humans can’t or can barely hear it (some animals are more sensitive)
In that reading all the sound frequencies between 20 and 20,000 Hz are weighted equally why is this not appropriate for psychologists?
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.
How can a more psychologically relevant measure of sound intensity be obtained?
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
What are measures of sound amplitude made using this human sensitivity weighting function called?
dB(A) measures.
What does the huge differences between dB SPL and dB(A) measures imply?
That there is a great deal of energy in the classroom in frequency bands which are unimportant for human perception.
Filtering
Excluding some frequencies and passing others
What frequencies does the ear exclude
under 20Hz and over 20,000Hz (may be present but d not affect the auditory system)
What is a filter function?
The response of a single auditory neuron (coming from the cochlea) to sound stimuli of various frequencies
True or false?
If the auditory system is damaged or dysfunctional the band of frequencies becomes much wider?
Trie
What is the restricted band of frequencies around the test tone which is important for your detection of that test tone called?
Critical band, at 2000Hz and is about 300Hz wide
What exactly is lost during hearing loss and what do test find on these people?
Loss of receptor hair cells.
Broader critical bands
auditory masking
Reduced audibility of a sound signal when in the presence of a second signal of higher intensity within the same critical band
Leaving away from industrialised areas suggests more or less hearing loss?
Less hearing loss (Easter Islanders)
In typical hearing loss other than the sound becoming weaker what else happens?
Major changes in how the sounds are processed.
Causing distortions and hampers speech comprehension
What is a voltage that varies overtime called?
A waveform
What is a waveform of a pure tone called?
A sine wave
How is a complex waveform related to simple sine waves?
a complex waveform can be broken down into simple sine waves or built up from them (via addition)
What is the frequency of a waveform with 4 msec between peaks?
250Hz
What is the quality of sound called?
Timbre
How large a difference in frequency was needed for you to detect a difference between that (variable frequency) test tone and a 500Hz tone?
Under optimal conditions (not true here) good observers can detect the difference between 500 and 502 Hz , just 2 Hz
Low-pass filtering a stimulus removes what frequencies…..?
Low pass filtering removes high frequencies (“passes” the low frequencies)
7. sounds become what you might describe as muffled
Low-pass filtering of speech has the same effect. Which group of people would experience such low-pass filtered speech….?
old people
