SHS 311 EXAM QUESTIONS WITH 100% CORRECT ANSWERS
What are the three types of temporal masking? - Answer- 1. Simultaneous masking
2. Forward masking
3. Backward masking
What is simultaneous masking? - Answer- Noise and masker overlap at the same time
Ex. Having a conversation with someone ...
What are the three types of temporal masking? - Answer- 1. Simultaneous masking
2. Forward masking
3. Backward masking
What is simultaneous masking? - Answer- Noise and masker overlap at the same time
Ex. Having a conversation with someone in a room (convo of about 65 dB) and hearing
a radio in the room as loud as a concert (about 120 dB) - You no longer can hear the
other person talking because you are completely masked out
What is forward masking? - Answer- Occurs when the masker precedes the signal (up
until 200 ms)
What is backward masking? - Answer- The masking of a tone by a sound that begins a
few milliseconds later (occurs when the masker follows the signal ) (up until 20 ms)
What is Spatial Hearing? - Answer- The ability to determine the location of a sound
source
- Important for detecting a sound source located outside the field of vision
What are three planes of 3-D space? - Answer- Near - far = distance (relative loudness
& reflections)
Left - right = interaural differences of time & level
Up - down = spectral differences from HRTFs
Why are ILDs greater at high frequencies? - Answer- - ILDs are produced by the inverse
square law and head shadow, the head shadow accounts for almost all of the ILDs
- ILD increases with increasing frequency
- ILD is larger when a sound comes from that side
Therefore, a sound with a frequency of 1944 Hz or higher would produce a sound
shadow on the other side of the head
Why are ITDs probably not a useful localization cue at high frequencies? - Answer- -
Due phase ambiguity
- Auditory nerve fibers do not phase lock on high frequency stimulus
For sound localization - At which frequency region do the greatest errors occur at the
Azimuth plane? - Answer- Localization errors increase around mid-frequency range,
, where ITDs are starting to cause phase ambiguity and ILDs are not strong enough to
produce and appreciable sound shadow
- neither ILDs or ITDs provide good cues for sound localization
What is the Duplex theory of Sound Localization? - Answer- The way in which ILDs and
ITDs are physically different as a function of frequency and that localization errors occur
at the middle frequencies lead to this theory
What are the cues for sound localization in the horizontal plane? - Answer- - High
frequency sounds are located in the azimuth plane based on ILDs
- Low frequency sounds are located in the azimuth plane based on ITDs
* The dividing line between low and high frequencies is between 1200 and 1600 Hz
What are the two types of localization tasks? - Answer- 1. Identification
2. Discrimination
(Localization Task) What does identification determine? - Answer- How well does the
perceived location align with the presented location of a sound source?
- For a broadband noise containing a range of frequencies, both ILDs and ITDs are
useable cues
(Localization task) What does discrimination determine? - Answer- How well can
subjects detect a small change in the sound location?
- To determine the smallest separation between two otherwise identical sound sources
that can be discriminated
What is MAA? - Answer- The smallest discriminable separation (Minimum Audible
Angle)
How is MAA measured? How does MAA change with frequency and with reference
azimuth position? - Answer-
What is a cone of confusion? - Answer- Source locations that produce sounds with the
same ILDs and ITDs, but the sources are located in different positions in 3-D space
What is the cue for sound localization in the vertical direction? - Answer- - Spectral
notches
- Very dependent on elevation
What are the two cues for distance localization? - Answer- - Relative loudness
- Reflections
What is relative loudness? - Answer- The level of sound decreases as the distance
between the source and ear increases
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