Lecture 2 Flashcards
In what 2 situations do you need masking?
- One ear is significantly poorer than the other (could be hearing in better ear)
- You are testing with bone conduction (bc bone conducted sound stimulates both cochleae at a similar level)
What is interaural attenuation?
-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
What is crossover?
-How much sound energy crosses or leaks to the other side (primarily via bone vibrations)
The amount of energy lost when crossing from one ear to the other is called ___ ___
Interaural attenuation
What is cross-over equal to?
Presentation level minus interaural attenuation
Cross-hearing vs cross-over
-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)
T/F: the cadaver head study revealed transcranial attenuation was larger for low frequencies
FALSE: transcranial attenuation is larger for HIGH frequencies (~5-10 dB)
What IA values should we use for TDH and ER-3?
-TDH: 40 dB
-ER-3: 50 dB
When do you mask for bone?
Whenever there is any significant air-bone gap (usually an ABG > 10 dB)
T/F: masking is when we cover up a tone with noise
FALSE: it’s how the sensitivity to one sound is affected by the presence of another sound
How much pressure does the tone need to have in the presence of a 100 dB SPL masker in order to be heard?
~70 dB SPL
How well (how many dB) can we discriminate intensity for tones at a high level?
~0.4 dB
T/F: audiometric masking always uses noise
TRUE: narrowband noise for tones and speech-shaped noise for speech
Band noise level vs spectrum level
-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’
Equation for spectrum level
Spectrum level = band level - 10log_10 (bandwidth)
Are audiometric maskers specified in dB SPL or dB HL?
Naur
Are audiometric maskers spectrum or band levels?
Naur
Fletcher’s Critical Band Theory
-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
T/F: CB width at 1000 Hz is 63 Hz
FALSE: this was Fletcher’s theory but he was wrong. It’s more like 150 Hz at 1000 Hz
Where did Fletcher go wrong?
He assumed that the band level has to be equal to the tone level, but this is wrong! Masking is NOT covering up
What is effective masking level (EML)?
It equals the level to which it masks a pure tone (i.e., 40 dB EML masks a pure tone to 40 dB HL)
T/F: 50 dB EML equals 50 dB HL
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
Amount of masking vs EML
-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
Basic Principle #1 of Masking
Put in enough masking to the NTE to shift the threshold in the NTE (and check the threshold in the TE again)
What is minimum masking?
5 dB above threshold of NTE
Basic Principle #2 of Masking
Don’t put too much masking in the NTE (you don’t want masker to cross over to the TE)
What is maximum masking?
The safest level of masking before overmasking
T/F: interaural attenuation can never be less than ABG
TRUE
Are we more concerned about over-masking in SNHL or CHL?
CHL
