Auditory Localization in Rooms: Acoustic Analysis and Behavior

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

3. center wall corner back 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°, 0.15-1m Positions of KEMAR and listeners Positions of sound source Room 5x9 meters, T60 ~700 ms

4. HRTF analysis Reverberation Alters Spectral Cues Anechoic Reverberant Left Ear Normalized Amplitude Frequency Spectrum (dB) Anechoic Reverberant Right Ear 0 50 100 150 200 0.1 0.5 1 5 10 Time (ms) Frequency (kHz)

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

7. Anechoic ITDs and Reverberation Source Distance 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 distanceMagnitude of x-corr peakdecreases with distance and with number of nearby wallsSecondary x-corr peak can be larger than primary 0.2 0.0 0.8 0.6 ITD (ms) 0.4 0.2 0.0 0 30 60 90 0 30 60 90 0 30 60 90 Source Azimuth (degs)

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

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 similar2) 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