Lecture 2

Question 1

In what 2 situations do you need masking?

Answer 1

1. One ear is significantly poorer than the other (could be hearing in better ear)
2. You are testing with bone conduction (bc bone conducted sound stimulates both cochleae at a similar level)

Question 2

What is interaural attenuation?

Answer 2

-How much sound energy is lost ‘interaurally’ (i.e., between the ears)
·Most of this is lost from headphone to bone, very little lost after that

Question 3

What is crossover?

Answer 3

-How much sound energy crosses or leaks to the other side (primarily via bone vibrations)

Question 4

The amount of energy lost when crossing from one ear to the other is called ___ ___

Answer 4

Interaural attenuation

Question 5

What is cross-over equal to?

Answer 5

Presentation level minus interaural attenuation

Question 6

Cross-hearing vs cross-over

Answer 6

-Cross-Hearing: HEARING it on the other side instead of the test side
-Cross-Over: sound leaking to the other side (but not necessarily heard on other side)

Question 7

T/F: the cadaver head study revealed transcranial attenuation was larger for low frequencies

Answer 7

FALSE: transcranial attenuation is larger for HIGH frequencies (~5-10 dB)

Question 8

What IA values should we use for TDH and ER-3?

Answer 8

-TDH: 40 dB
-ER-3: 50 dB

Question 9

When do you mask for bone?

Answer 9

Whenever there is any significant air-bone gap (usually an ABG > 10 dB)

Question 10

T/F: masking is when we cover up a tone with noise

Answer 10

FALSE: it’s how the sensitivity to one sound is affected by the presence of another sound

Question 11

How much pressure does the tone need to have in the presence of a 100 dB SPL masker in order to be heard?

Answer 11

~70 dB SPL

Question 12

How well (how many dB) can we discriminate intensity for tones at a high level?

Answer 12

~0.4 dB

Question 13

T/F: audiometric masking always uses noise

Answer 13

TRUE: narrowband noise for tones and speech-shaped noise for speech

Question 14

Band noise level vs spectrum level

Answer 14

-Band noise level: the overall level of that noise (across the noise’s frequency bandwidth)
-Spectrum level: refers to the level in a 1 Hz wide band, also called ‘level per cycle’

Question 15

Equation for spectrum level

Answer 15

Spectrum level = band level - 10log_10 (bandwidth)

Question 16

Are audiometric maskers specified in dB SPL or dB HL?

Answer 16

Naur

Question 17

Are audiometric maskers spectrum or band levels?

Answer 17

Naur

Question 18

Fletcher’s Critical Band Theory

Answer 18

-A tone would be just masked when the energy of the tone and the masker are equal (i.e., when the band level of the noise is the same as the tone)
-He reasoned that the overall level of the noise in a ‘critical band’ must be 58 dB SPL

Question 19

T/F: CB width at 1000 Hz is 63 Hz

Answer 19

FALSE: this was Fletcher’s theory but he was wrong. It’s more like 150 Hz at 1000 Hz

Question 20

Where did Fletcher go wrong?

Answer 20

He assumed that the band level has to be equal to the tone level, but this is wrong! Masking is NOT covering up

Question 21

What is effective masking level (EML)?

Answer 21

It equals the level to which it masks a pure tone (i.e., 40 dB EML masks a pure tone to 40 dB HL)

Question 22

T/F: 50 dB EML equals 50 dB HL

Answer 22

FALSE: effective masking level is not equal in energy to the tone it masks. You can figure out the actual dB SPL or dB HL with the critical band

Question 23

Amount of masking vs EML

Answer 23

-Amount of masking: amount of threshold shift (e.g., 10 dB threshold —> 80 dB threshold after masking so amount of masking is 70 dB)
-EML: the dial level

Question 24

Basic Principle #1 of Masking

Answer 24

Put in enough masking to the NTE to shift the threshold in the NTE (and check the threshold in the TE again)

Question 25

What is minimum masking?

Answer 25

5 dB above threshold of NTE

Question 26

Basic Principle #2 of Masking

Answer 26

Don’t put too much masking in the NTE (you don’t want masker to cross over to the TE)

Question 27

What is maximum masking?

Answer 27

The safest level of masking before overmasking

Question 28

T/F: interaural attenuation can never be less than ABG

Answer 28

TRUE

Question 29

Are we more concerned about over-masking in SNHL or CHL?

Answer 29

CHL