Chapter 5: Masking Flashcards
Three Big Questions
1.) Is masking needed?
2.) How much masking is required?
3.) At what point might the masking directed to the non-test ear reach an intensity that could cross over to the test ear and confound the test results?
Interaural Attenuation
The amount of energy lost as sounds travel from one side of the head to the other
IA for inserts
75dB for 250Hz-1000Hz
50dB for frequencies greater than 1000Hz
IA for supra-aural headphones
40dB
IA for bone conduction
Theoretically as low as 0 dB
When does cross hearing most commonly occur
through bone conduction
What is the most effective masking signal for pure tones?
Narrowband noise
Effective Masking
-Minimum amount of noise required to make a given signal inaudible
-The effective masking level is used as a starting point to finding the true threshold of the test ear
Overmasking
When the masking noise is so intense in the masked ear that it crosses the skull and produces an undesired masking of the test signal in the test ear
When is masking needed? - Bone Conduction
when the air-bone gap (A B G) is greater than 10 deciBel, one cannot be certain which cochlea is receiving the tone
Central Masking
Small shift seen in the threshold of a pure tone due to masking noise in the opposite ear (averages about 5dB)
When is masking needed in air conduction?
the tone in the test ear minus the IA is equal or greater than the BC threshold of the nontest ear
How much masking for air conduction?
effective masking level = ac threshold of nte+correction factor
Plateau Method for Masking
Once threshold is obtained, apply masking to nte. If tone is not heard raise it by 5dB. Once it is heard 3 times while it is increasing by 5dB every time without the tone changing, masking was done correctly. Level of tone doesn’t need to be raised when noise is increased
Occlusion Effect
the perceived intensity of low frequency tones is actually increased. can effect masking
