wave field synthesis: basics and applicationsdafx09.como.polimi.it/data/wfs_dafx_0909.pdf ·...

Prof. Dr.-Ing. Karlheinz Brandenburg, [email protected] 2009-09-02

Wave Field Synthesis:

Basics and Applications

Karlheinz Brandenburg, Sandra Brix, Thomas Sporer

Technische Universität Ilmenau

Fraunhofer Institute for Digital Media Technology IDMT

llmenau, Germany


Overview

• Why do we need a new sound system ?

• Theory of WFS

• Applications

– Movie theatres

– Live performances

• Conclusions


Blind testing 100 years ago

Sou

rce:

blu

egu

m /

SXC

.hu


Starting with Mono ...


... via Stereo ...


... to 5-channel stereo


but still not perfect

Sweet Spot


in the living room

Sweet Spot


in the living room

Sweet Spot ???


In the cinema

Sweet Spot ???


Basic Idea of Wave Field Synthesis (WFS)

Sou

rce:

htt

p://

ress

ou

rces

2.te

chn

o.f

ree.

fr/in

form

atiq

ue/

site

s/in

ven

tio

ns/

inve

nti

on

s.h

tml

Christof Huygens • 17th century

• Work on light waves

Guus Berkhout/ Diemer De Vries (TUD) • 20th century

• Work on acoustic waves


Delay Amplitude adjustment

Primary Source

Secundary Source

Diemer de Vries, Rinus Boone (TUD) Redrawn by Frank Melchior (IDMT)

Wave Field Synthesis (WFS)


The Kirchhoff-Helmholtz Integral

Vn - component of particle velocity in rS,

P - pressure,

- density function SV

n

r rS

rR


distribution of monopoles distribution of dipoles

R

3D Kirchhoff-Helmholtz Integral (Space-Freq. Domain)


• 3D Kirchhoff-Helmholtz-Integral:

• 3D Rayleigh-Integral I:

3D Rayleigh Integral I – Monopoles only


• 3D Kirchhoff-Helmholtz-Integral:

• 3D Rayleigh-Integral II:

3D Rayleigh Integral II – Dipoles only


• Adaptation 3D -> 2 D (linear loudspeaker arrays)

• Finite length of loudspeaker arrays

• Discrete loudspeaker distance

• Enclosing listeners with loudspeakers

See (many) papers

Next Steps


Wave Field Synthesis

• The sound is perceived from a certain position behind the loudspeakers

• … creates a wave field within the listening area

• A large number of separately controlled loudspeakers …


• The sound is perceived from a certain position behind the loudspeakers

• … creates a wave field within the listening area

• A large number of separately controlled loudspeakers …




focused source

• Three types of sound sources – Point sources

– Plane waves

– Focused sources

• Signal at each loudspeaker defined by delay and amplitude

• Moving sources create Doppler shift


sound hologram

Wave Field Synthesis in the living room


sweet spot “virtual loudspeakers”

... using Wave Field Synthesis


• Perfect »sound hologram« – Within encircled area

– Up to alias frequency

– Ability to simulate room effect

– Natural Doppler effect

– Ability to compensate for reproduction room

– Compatible to 2.0/5.1/…

Wave Field Synthesis - Properties


WFS – File Format

• Storing of audio objects – Point sources (sound and position)

– Plain waves (sound and direction)

– (distributed objects)

• Rendering at reproduction site to

– WFS

– (Higher Order) Ambisonics

– 22.2, 5.1, stereo

– Head phones (w/wo head tracking)

Don't mix down in studio

Keep decision open


WFS: How to create perfect illusion ?

• Up to now, physics centered view – Wave equations

• Psychoacoustics

– Spatial hearing: we got just two ears, but …

– Cone of confusion

– Height perception: Blauert bands

– Binaural cues

• ITD

• ILD

• Correlation

– Head Related Transfer Functions (HRTF)


More about spatial hearing

• Sense of direction – ITD, ILD, HRTF

• Sense of distance

– Curvature of wave field

– Loudness

– Air as a filter

• We can build simulated plane waves sounding near

• Everything goes through processing in the brain


Recognizing rooms

• Blind people detect a wall from the sound of their foot steps

• We all can recognize rooms from listening to reflections

• There are different theories of how we do this

– Just from binaural cues

– Or do we have a auditory picture in our brain ?

• Anyway: playing WFS in a room with natural reflections can destroy the illusion


WFS – Technological Challenges Today (1)

• Compensate for room acoustics (dereverb)

• Compensation of loudspeaker characteristics

• Far field / near field

– position dependent filtering

• Incomplete loudspeaker setups

– position dependent level adjustment

– smart interpolation algorithms


WFS – Technological Challenges Today (2)

• Moving sound sources – Interpolation

• Doppler suppression

– Unwanted natural Doppler (music)

– Unnatural Doppler

• Complex scenes

– Rain

– Applause

Algorithms mostly available, but not the hardware (at reasonable price)


Application example: Cinema Ilmenau

• 192 loudspeaker WFS

• WFS trailer shown before all exhibitions

• compatible reproduction of all films in WFS

• in operation since 2003


Application example: Authoring System

• screenshot


Bregenzer Festspiele 2008 (open air opera)

• 800 loudspeaker

• WFS around audience

• 100 loudspeaker BOA for stage

• 7000 seats


Bregenzer Festspiele 2008 (open air opera)


München/Germany: Bavaria Filmstadt

Sou

rce:

Bav

aria

Film

stad

t (2

)


Application Example: Museum and Exhibition

• Spanish Pavilion at Expo 2008 in Zaragoza, Spain

Sou

rce:

IOSO

NO

Gm

bH


Zürich: Multi-Modal Motion Synthesis Lab of ETH

Sou

rce:

IOSO

NO

Gm

bH


Los Angeles: Museum of Tolerance/Simon Wiesenthal Center

Sou

rce:

IOSO

NO

Gm

bH

(2)


Hollywood: Chinese 6, Mann Theatres

Sou

rce:

IOSO

NO

Gm

bH


The future: Wave Field Synthesis at home?


• Mono -> stereo -> WFS!!

• After years, computational complexity is no longer an obstacle

• WFS is especially suited for large audiences (with some problems !)

• WFS brings new artistic possibilities

• Until now, good sound was only there for “natural” environments without amplifiers

This will change.

Conclusion

wave field synthesis: basics and applicationsdafx09.como.polimi.it/data/wfs_dafx_0909.pdf ·...

Documents