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Localization of a virtual point source within the listening area for Wave Field Synthesis

Hagen Wierstorf1, Alexander Raake1, Sascha Spors2

1Assessment of IP-based Applications, Technische Universität Berlin 2 Institute of Communications Engineering, Universität Rostock

• 27. October 2012

Wave Field Synthesis (WFS)

correct field for the whole listening area

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.20 m, f = 1 kHz virtual source

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 1 / 18

Wave Field Synthesis (WFS)

artefacts in the whole area

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.41 m, f = 1 kHz virtual source

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 1 / 18

Research questions

Is the localization in Wave Field Synthesis equal over the whole listening area? How to assess the localization within the whole listening area? How many speakers do we need for correct localization?

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 2 / 18

Theoretical considerations

law of the first wave front

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.20 m virtual source

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 3 / 18

Theoretical considerations

law of the first wave front

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.41 m virtual source

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 3 / 18

Theoretical considerations

law of the first wave front

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 1.43 m virtual source

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 3 / 18

Localization in WFS

results from the literature

Localization is the same for real and virtual sources for loudspeaker spacings around 0.12 cm Localization is slightly worse for virtual sources for loudspeaker spacings around 0.24 cm We are not interested in the influence of the reproduction room the ease of localization

Vogel (1993), Application of Wave Field Synthesis in Room Acoustics, Delft Start (1997), Direct Sound Enhancement by Wave Field Synthesis, Delft Verheijen (1997), Sound Reproduction by Wave Field Synthesis, Delft Wittek (2007), Perceptual differences between Wave Field Synthesis and stereophony, Surrey

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 4 / 18

Localization in WFS

results from the literature

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Vogel (1993)

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 5 / 18

Localization in WFS

results from the literature

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Vogel (1993)

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 5 / 18

Localization in WFS

results from the literature

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Start (1993)

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 5 / 18

Localization in WFS

results from the literature

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Verheijen (1997)

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 5 / 18

Localization in WFS

results from the literature

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Wittek (1997)

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 5 / 18

Localization in WFS

what we want to do

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 6 / 18

Localization in WFS

what we want to do

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 6 / 18

Localization in WFS

what we want to do

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 6 / 18

Localization in WFS

How to measure localization in the whole listening area?

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 7 / 18

Binaural synthesis

connection between sound field synthesis and psychoacoustics (Völk, 2008) dynamic binaural synthesis via head tracker transparent with individual HRTFs (Langendijk, 2000)

Völk et al. (2008), Simulation of wave field synthesis, Acoustics Langendijk und Bronkhorst (2000), Fidelity of three-dimensional-sound reproduction using a virtual auditory display, JASA Wierstorf et al. (2011), A free database of head-related impulse response measurements in the horizontal plane with multiple distances, 130thAES

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 8 / 18

Binaural synthesis

connection between sound field synthesis and psychoacoustics (Völk, 2008) dynamic binaural synthesis via head tracker transparent with individual HRTFs (Langendijk, 2000)

Völk et al. (2008), Simulation of wave field synthesis, Acoustics Langendijk und Bronkhorst (2000), Fidelity of three-dimensional-sound reproduction using a virtual auditory display, JASA Wierstorf et al. (2011), A free database of head-related impulse response measurements in the horizontal plane with multiple distances, 130thAES

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 8 / 18

Binaural synthesis

connection between sound field synthesis and psychoacoustics (Völk, 2008) dynamic binaural synthesis via head tracker transparent with individual HRTFs (Langendijk, 2000)

Völk et al. (2008), Simulation of wave field synthesis, Acoustics Langendijk und Bronkhorst (2000), Fidelity of three-dimensional-sound reproduction using a virtual auditory display, JASA Wierstorf et al. (2011), A free database of head-related impulse response measurements in the horizontal plane with multiple distances, 130thAES

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 8 / 18

Binaural synthesis

connection between sound field synthesis and psychoacoustics (Völk, 2008) dynamic binaural synthesis via head tracker transparent with individual HRTFs (Langendijk, 2000)

Völk et al. (2008), Simulation of wave field synthesis, Acoustics Langendijk und Bronkhorst (2000), Fidelity of three-dimensional-sound reproduction using a virtual auditory display, JASA Wierstorf et al. (2011), A free database of head-related impulse response measurements in the horizontal plane with multiple distances, 130thAES

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 8 / 18

Procedure

Pre-test: Verification of binaural synthesis Main test: Localization within a sound field for WFS

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 9 / 18

Apparatus

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 10 / 18

Apparatus

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 10 / 18

Pre-test: Verification of binaural synthesis

method

head-pointing method with laser pointer mounted on the head (Makous 1990) ⇒ listener has to face the source, smallest human localization error (Mills 1958) ⇒ laser pointer gives visual feedback and enhances the cooperation with the motor system (Lewald 2000) white noise pulses 700 ms long, 300 ms pause 11 subjects, central position 22 conditions: 11 different positions of the virtual source/loudspeaker all randomized, 5 repetitions for each condition

Makous and Middlebrooks (1990), Two-dimensional sound localization by human listeners, JASA Mills (1958), On the minimum audible angle, JASA Lewald et al. (2000), Sound localization with eccentric head position, Behav Brain Res

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 11 / 18

Pre-test: Verification of binaural synthesis

mean results + 95% confidence interval

−6◦ 0◦ 6◦ −6◦ 0◦ 6◦ −45◦ −30◦ −15◦ 0◦ 15◦ 30◦ 45◦ φauditory event − φsound event φsound event

loudspeaker mean error: 2.4◦ binaural synthesis mean error: 2.0◦

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 12 / 18

Localization within a sound field for WFS

method

−4 −3 −2 −1 1 −3 −2 −1 1 2 3 y/ m x/ m

white noise pulses 700 ms long, 300 ms pause 11 subjects, 16 different positions 3 conditions: 2.85 m loudspeaker array consisting of 3, 8, or 15 loudspeakers simulated by dynamic binaural synthesis all randomized, 5 repetitions for each condition and position

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 13 / 18

Localization within a sound field for WFS

mean results

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.20 m mean error: 1.8◦ maximum error: 2.5◦

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 14 / 18

Localization within a sound field for WFS

mean results

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 0.41 m mean error: 2.7◦ maximum error: 4.4◦

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 14 / 18

Localization within a sound field for WFS

mean results

−2 −1 1 −2 −1 1 2 y/ m x/ m

loudspeaker spacing: 1.43 m mean error: 6.6◦ maximum error: 11.4◦

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 14 / 18

Conclusion

Is the localization in Wave Field Synthesis equal over the whole listening area? Localization is equal, only for loudspeaker spacings of more than 1 m sweet spot like distributions occur How to assess the localization within the whole listening area? With dynamic binaural synthesis. full control of stimuli reaching the listener every position and loudspeaker array possible How many loudspeakers do we need for correct localization? A loudspeaker distance of 20 cm is transparent, 40 cm still sufficient for localization

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 15 / 18

Open Questions

what is the influence of the reproduction room? is the ease of localization affected? can these questions be investigated by binaural synthesis? focused sources, plane waves different array geometries, for example circular

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 16 / 18

Open Questions

Coloration

−110 −100 −90 −80 −70 −110 −100 −90 −80 −70 10 100 1000 10000 amplitude / dB center frequency / Hz

loudspeaker spacing: 0.001 m loudspeaker spacing: 0.2 m

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Questions?

http://audio.qu.tu-berlin.de/

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Further analysis

interaural time differences

0.2 0.4 0.6

listener at (−0.25, −1.5) m

0.2 0.4 0.6 interaural time difference / ms 0.2 0.4 0.6 289 414 569 761 1k 1.3k center frequency / Hz

loudspeaker spacing: 0.20 m loudspeaker spacing: 0.41 m source at desired direction source at perceived direction virtual source (WFS) loudspeaker spacing: 1.43 m

Wierstorf, Raake, Spors Localization within the listening area for WFS 12/10/27 19 / 18