1. Auditory Localization in Rooms: Acoustic Analysis and Behavior
Norbert Kopčo1
Barbara Shinn-Cunningham1,2
Boston University Hearing Research Center
1Cognitive and Neural Systems, Boston University
2Biomedical Engineering, Boston University

2. Localization in a room:
Degraded directional hearing Improved distance perception
Goal:
Analyze how localization cues are influenced by
listener position in a room
source azimuth and distance around listener
Compare predictions to behavior
Outline:
Effect of Room on Spatial Cues:
Spectral Cues, Interaural Level Differences, Interaural Time Differences
Human Localization Performance
Conclusions and Future work

3. Methods Measure KEMAR HRTFs
4 room positions, azimuths 0 – 90° (15° steps), dist 15, 40, 100 cm
Analyze effect of reverberation on ILD, ITD, spectrum
In terms of mean value and variability
Human performance
mean and std dev in perceived azimuth within 0-90°, m
Positions of KEMAR and listeners
Positions of sound source
Room 5x9 meters, T60 ~700 ms
center
wall
corner
back

4. Reverberation Alters Spectral Cues
HRTF analysis
Reverberation Alters Spectral Cues
Anechoic
Reverberant
Left Ear
Normalized Amplitude
Frequency Spectrum (dB)
Anechoic
Reverberant
Right Ear 50
100
150
200
0.1
0.5 1 5 10
Time (ms)
Frequency (kHz)

5. Magnitude Spectrum (dB)
Reverberation Effects Depend on Source Direction, Increase with Distance
0˚ azimuth
90˚ azimuth
Left
Right
Left
Right
15 cm
Anechoic
Anechoic
Reverberant
Reverberant
Magnitude Spectrum (dB)
200 cm
0.1 1 10
0.1 1 10
0.1 1 10
0.1 1 10
Frequency (kHz)

6. ILDs and Reverberation
Source Distance
Anechoic
ILDs smaller: - with distance and with asymmetric reflections ILD variability: - 0 in anechoic - increase with distance - largest in Center

7. ITDs and Reverberation
Source Distance
Anechoic
0.15 m
0.40 m
1 m
1.0
0.8
0.6
X-Corr Peak Coeff
0.4
ITD of x-corr peak independent of position or distance Magnitude of x-corr peak decreases with distance and with number of nearby walls Secondary x-corr peak can be larger than primary
0.2
0.0
0.8
0.6
ITD (ms)
0.4
0.2
0.0 30 60 90 30 60 90 30 60 90
Source Azimuth (degs)

8. Reverberation and ITD Variation
Anechoic baseline
Variation is random around mean in Center (and Back ) In Corner (and Ear) the early asymmetric reflections are have more pronounced effect
0.8
0.6
ITD (ms)
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
200
600
1000
1400
1800
200
600
1000
1400
1800
Frequency (Hz)

9. Human performance
Two significant trends: 1) In Back and Corner, bias towards median plane (3.5°) - no correlation with acoustics where Corner and Ear similar 2) Variance in azimuth increases from Center to Corner - consistent with variability in ITD and ILD - however, not consistent as a function of distance

10. Conclusions and discussion
All localization cues affected strongly by reverberation in a room position dependent way
Localization performance affected modestly
Possible explanations:
humans are sensitive to changes in cues over time (precedence effect)
listeners are able to estimate effect of reverberation and compensate for it
Future work:
apply models of auditory processing (Colburn, 1977) to predict how cues are extracted from reverberant signals in the brain
look at effects of learning (Kopčo et al., 2001) on localization in rooms