Simulating distance cues in virtual reverberant environments

1. Simulating distance cues in virtual reverberant environments • Norbert Kopčo1, Scott Santarelli, Virginia Best, • and Barbara Shinn-Cunningham • Hearing Research Center • Boston University • and • 1Technical University of Košice • Slovakia

2. For sources near the listener (e.g., distance < 1m):- Interaural level differences change as a function of distance (Brungart & Rabinowitz, 1999; Shinn-Cunningham et al., 2000). Introduction Main goal:Illustrate that binaural simulation of nearby sources in reverberation effective in providing distance information without distorting other aspects of the stimuli. - ILDs can be used as absolute distance cue (and they are used as such in real anechoic space; Brungart, 1999). - In reverberant space, D/Rs are large, and received sounds are not strongly influenced by reverberation (Shinn- Cunningham et al., 2006).

3. Exp. 1. Compare nearby-source distance perception in real anechoic and reverberant environments. Overview Present results of three experiments that study distance perception for nearby sources in real and simulated environments.Consider cues used by listeners.Suggest implications for auditory displays. Exp. 2. Measure performance in virtual environment, look at importance of ILD and reverberation cues. Exp. 3. Study frequency-dependence of performance in simulated reverberation.

4. Goal:Compare nearby-source distance perception in real anechoic and reverberant environments.Hypothesis: Performance will be similar because reverberation energy is low for nearby sources. Exp. 1: Real Environments

5. Stimuli: - broadband pink-noise bursts,- presented at various azimuths, 0.12 to 1 m from listener roving the presentation level,- in a small classroom (T60 ~0.6 sec).Response:- pointing to perceived target location using a wand with electromagn.sensor. Exp. 1: Real Environments - Methods Analysis:- Bin data by target lateral angle.- Compute correlation coefficient r between actual and perceived stimulus distance (on a log scale) in each lateral bin.- Compare to results of a similar experiment performed in anechoic chamber (Brungart, 1999).

6. When simulating distance, choose virtual reverberant space (even for nearby sources) because it provides better accuracy. Exp. 1: Real Environments - Results Anechoic (Brungart, 1999):- good for lateral sources,- bad for medial. Reverberant:- similar to anechoic for lateral sources,- very good for medial.

7. Goals:Compare real and virtual environments.Analyze contribution of ILD and reverberation cues.Hypothesis: Performance similar (or slightly worse in virtual environment because of limitations of simulation).ILD used equally in anechoic and reverberant environments. Exp. 2: Virtual Environments

8. Similar to Exp. 1, except:- virtual environment,- only two directions: medial and lateral,- binaural and (ipsi) monaural presentation modes,- blocks of 45 trials, keeping direction and presentation mode constant,- blocks randomly interleaved, - responding by a mouse click on a computer screen. Exp. 2: Virtual Environments - Methods

9. Exp. 1 Exp. 2: Virtual Environments - Results Anechoic:- performance below chance. Reverberant:- small drop in correlation re. real environment (Exp. 1) (by .1 to .2 for lat and for med) • independent of mon/binaural presentation mode

10. Exp.2: Virtual Environments - Discussion Why anechoic simulation poor:- technical limitations, - varying simulated environment. Why ILD not used:- Not clear, but a follow-up confirmed that ILD was perceptible. D/R changes sufficient to explaindifference between lat/med. When simulating distance, choose virtual reverberant space – simulation is more robust.

11. Exp. 3: Spectral Content Goals:In anechoic environment, distance perception deteriorates for high-frequency lateral sources (Brungart, 1999). Measure frequency dependence in reverberation.Hypothesis: In reverberation, dependence on spectral content will be different (compared to anechoic environment), because of the dominant reverberation cues.Methods: Similar to Exp. 2, except:Stimuli are 200-Hz wide noise bursts centered at .4, 3, and 5.7 kHz.

12. Exp. 3: Spectral content - Results At low frequencies:Both lat and med performance very good (med better than broadband data from Exp. 2). At higher frequencies:- Lateral: drops slightly.- Medial: drops strongly.

13. When simulating distance, choose virtual reverberant space – performance is less frequency dependent. Exp. 3: Spectral content - Discussion Difference in spectral effect re. anechoic:- not consistent with ILD or reverberation-related cue. Improvement in medial performance over Exp. 2:- possible effect of adaptation to environment (inconsistent in Exp. 2)- similar effects shown in learning studies (School- master et al., 2004)

14. Conclusions • Technology used to simulate auditory distance should use reverberant simulation because it is • more accurate (even in real environment), • less sensitive to simulation quality and stimulus spectrum. • Good news: The simulation • does not need to be binaural, • might not need to require nearby sources if reverb-related distortions don’t matter (as ILDs do not contribute), • might require to be consistent. • Bad news: Even simulation that includes reverberation does not provide usable cues for frontal high-frequency stimuli  relative cues (e.g., overall level) may be required. • Research supported by US AFOSR, US National Institutes of Health, US National Academy of Sciences and Slovak Science Grant Agency