12 - Masking Mechanisms and EM Flashcards
Describe “Effective masking”
The ability of a masking noise to “cover” or mask a signal of known frequency and intensity in the SAME ear
What is EML?
The Effective Masking Level
- the minimum level of masking noise that renders a signal inaudible in the same ear.
- for a pure tone signal, this is the NBN level that just barely masks the tone
What is dB EM?
decibels of effective masking
True or False: The detection threshold of a sound/signal is decreased by the presence of another sound (masker)
False; the threshold is increased
What units are masking noise signals measured/calibrated to on the audiometer?
dB EM
*NOT dB HL
E.g. 1 kHz pure tone of 30 dB HL is masked by 1 kHz NBN at 30 dB EM
Effectiveness of the masker depends on cochlear/neural activity patterns associated with what 2 things?
- signal frequency bandwidth and level
- masker frequency bandwidth and level
White noise can mask a pure tone, so why don’t we use it instead of narrow band noise?
White noise would excite more neurons and increase the perceived loudness of the masker
If a pure tone signal is most effectively masked by a pure tone of similar frequency, why don’t we use pure tone maskers in audiology?
Because the patient can’t differentiate between the signal tone and masker tone
What makes NBN (narrow band noise) a good choice of masker?
It can effectively mask a pure tone while evoking less neural activity than white noise
What does “0 dB EML” mean?
The lowest level of noise (dB SPL) rendering the signal inaudible IN THE SAME EAR
The NBN level (dB SPL) must be _____ (the same as/slightly higher than) the pure tone level (dB SPL) to achieve “effective” masking
Slightly higher than
On a graph of the pure tone threshold shift and NBN Masker Level, where would we see 0 dB EM?
At the kneepoint (ie. where the line starts to ascend)
What is another name for the built-in correction factor for clinical audiometers masking channels (calibrated in EML)?
MEMC (Minimum Effective Masking Correction)
