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3D sound reproduction with “OPSODIS”3D sound reproduction with “OPSODIS”andand

its commercial applicationsits commercial applications

Takashi Takeuchi, PhD Takashi Takeuchi, PhD

Chief Technical OfficerChief Technical Officer

OPSODIS LimitedOPSODIS LimitedInstitute of Sound and Vibration Research, University of SouthamptonInstitute of Sound and Vibration Research, University of Southampton

Kajima Technical Research InstituteKajima Technical Research Institute

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History

　 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Student

University of Southampton

　 　 　 　 　 　 　 　 　 　 　 　 　 　

AcousticConsultant

(Kajima)

　 　 　 　 　 　 　 　 　 　 　 　 　 　

Staff ISVR

University of Southampton

　 　 　 　 　 　 　 　 　 　 　 　 　 　

3D soundBusiness

　 　 　 　 　 　 　 　 　 　 　 　 　 　

MSc PhD

Stereo Dipole OPSODIS (UK Ltd.)

OPSODIS

Joint R&D Joint R&D

Auralisation

(OPSODIS)(Invention)

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What is OPSODIS™?OpOptimal timal SoSource urce DisDistributiontribution

• Principle Principle - 3D sound reproduction- 3D sound reproduction -- Binaural Binaural -- Loudspeaker reproduction Loudspeaker reproduction -- 2 channel system (3ch option) 2 channel system (3ch option) -- Stereo & Surround Stereo & Surround -- reproduction compatible reproduction compatible

• What is special?What is special? - Lossless crosstalk cancellation!- Lossless crosstalk cancellation! -- Signal processing by loudspeaker Signal processing by loudspeaker -- Good & natural sound quality Good & natural sound quality -- Robust control Robust control -- Elevation (height) reproduction Elevation (height) reproduction -- Multiple listeners Multiple listeners

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Spatial hearing and binaural signal

Sound source signal

Binaural signals

• Physics　 source signal　　　　 propagation　　　　 two different signal at ears

• Perception　 Separates signal and spatial information　　　　 binaural signals

Characteristics of space (physics)Characteristics of space (physics)（（ relative positionrelative position ，， response of spaceresponse of space ））Spatial hearing (human)Spatial hearing (human)（（ source positionsource position ，， movementmovement ，， room sizeroom size，， reverberationreverberation ））

A1

A2

d

s

21

11

A

AA

Asd any number of sources …any number of sources …

stereosurround

binaural

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Inverse filtering (crosstalk cancellation)

• Loudspeaker reproduction interweaves loudspeaker position

• In order to reproduce spatial information arbitrarily, independent transmission to each ear is necessary.

• Minimum of two independent (real) sound source necessary

Synthesised binaural signals

C11

C21

C12

C22

2221

1211

CC

CCC

Inverse filtering

H

binaural Signals

d CHdw w

dw

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Conventional cross-talk cancellation

t

t

L

R

t

t

Right ear

Left ear

Cancelling each other

Left ear

Right ear

Independent control at both ears

t

t

Loudspeaker output

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Conventional cross-talk cancellation

t

t

L

R

t

t

Right ear

Left ear

Left ear

Right ear

Independent control at both ears

t

t

Loudspeaker output

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Conventional cross-talk cancellation

t

t

L

R

t

t

Right ear

Left ear

Loudspeaker output

Left ear

Right ear

Independent control at both ears

t

t

Massive destructive interference

Repetitive delay = Large output(Frequency dependent)

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Crosstalk cancellation (frequency)

Destructive interference at both ears. Inefficient, quality loss, sensitive to errors.

amplitudephase

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Frequency dependency

frequency

– from Left SP – from Right SP– reproduced frequency

Conventional

Right earLeft ear

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Frequency (linear)

level

20Hz 20kHz-40dB

0dB

Why have 3D systems not performed well so far?

in

out

Sound emitted by loudspeakers do not reach listener’s ears at certain frequencies.

Large output required to compensate it.

In-phase signal

Out-of-phasesignal

(_____ ) 　　　　　

Frequency response to listener

(_ _ _ )

(two point sources) 6dB

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Frequency

Loss of performance through cross-talk cancellation process

• Typical frequency response of the inverse filters

for 3D reproduction.

level

20Hz 20kHz-40dB

0dB

Out-of-phasesignal

In-phase signal

1e

e1

e1

1sinrj-

sinr-j

sinr2j-21

k

k

k g

g

gCH

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Loss of performance through cross-talk cancellation process

level

0dB

-30dB

Dynamic range loss = Low Quality

OriginalPerformance

Frequency20Hz 20kHz

Cross-talk cancellation degrades performance severely.

Synthesized sound

Distortion

Noise

Exact matching

≈ 5 bit

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Analogy to picture quality

Reduce;Constant resolution

Magnify; Pixel size

Quality Loss

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Loudspeaker span

frequency (log)

-16dB

Original Performance

Synthesized sound

180°

More complexity

Smaller loss

frequency

0 dB

-43dB

10°

Larger loss

Less complexity

≈ - 7 bit≈ - 3 bit

20Hz 20kHz 20Hz 20kHz

(Stereo Dipole)

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Optimal Source Distributionfr

eque

ncy

20kHz

0° 180°20Hzg

ood

poor

60° 120°

200Hz

2kHz

OPSODIS

Con

vent

iona

lC

onve

ntio

nal

high

frequency

low low

OPSODIS

transducer position

Transducer position vs Performance(excess amplification)

Conventional

Ste

reo

Dip

ole

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Conventional

OPSODIS

(Stereo Dipole)

The worst conditioned frequency dictates performancefor all frequencies!!

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OPSODIS loudspeaker• Frequency response to listener with OPSODIS.

frequency

level

-40dB

0dBOPSODIS

1j

j1C

No frequency dependency on amplitude response and phase response

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OPSODIS principle• Frequency response of the OPSODIS inverse filters.

frequency

level

•Simple process•No loss resulting from signal manipulations

•High quality 3D reproduction•Natural & pure sound quality•Elevation reproduction

-40dB

0dB

robust

H

1

1

1

11

2

1

12g

g

g

j

j

j

j

No frequency dependency on amplitude response and phase response

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Crosstalk cancellation of OPSODIS

Cancellation

Addition

Left ear

Right ear

Independent control at both ears

amplitudephase

L

R

Loudspeaker output

Right ear

Left ear

½ amplitude, -90º phase

½ amplitude

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Crosstalk cancellation of OPSODIS

Left ear

Right ear

Independent control at both ears

amplitudephase

L

R

Loudspeaker output

Right ear

Left ear

½ amplitude, -90º phase

½ amplitude

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Crosstalk cancellation of OPSODIS

Left ear

Right ear

Independent control at both ears

amplitudephase

L

R

Loudspeaker output

Right ear

Left ear

½ amplitude, -90º phase

½ amplitude

Destructive interference

Constructive interference

Efficient, Lossless, Robust to errors.

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frequency

Reproduction quality

frequency

– L channel– R channel– reproduced

Stereo Dipole

16 bit 16 bit≈9 bit

OPSODIS16 bit 16 bit

≈17 bit

Example: 16bit hardware

Reproduced dynamic range≈ -43 dB

Reproduced dynamic range≈ +3 dB

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Electro-acoustic transducer for OPSODIS

narrow slot wide

driverslot

high frequency low

plateshaker

large stiffness smallnarrow width wide

high frequency low

driving plate

•Flat panel loudspeakers

•Acoustic waveguidehigh frequency low

Variation in excited frequency and radiation impedance

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Discrete system

•2 channel, multi-way system•Use of conventional transducers•Wide frequency range

transducer span

freq

uenc

y(H

z)

•U-shaped valley

Small performance loss

n n 1 1 1 •Width of n enables discretisation

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Effects of room reflection (sound radiation)0 dB- dB 0 dB- dB

0 dB

Small radiation Small radiation by OPSODISby OPSODIS

Not affected by reflectionNot affected by reflection

Reference to radiation by mono loudspeaker

conventional OPSODIS

Very large sound radiation other than receiver directions

Needs anechoic room

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Radiation pattern of Conventional

• Radiation pattern is different depending on the frequency. • Single listener．• Very small sweet area.

0dB -∞dB

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0.6m 0.6m

A BBA A

Radiation pattern of OPSODIS

• Radiation pattern is constant regardless the frequency; Large sweet area• No spectral change; elevation works everywhere. • Multiple listener listening with a little performance loss. • The interval of L-R cross-talk cancellation is about 0.3m; Alternative

seating positions.

A: 1 or 3 listener(s)B: 2 listeners

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Reproduced sound level (lateral position）

• 3 seater or 2 seater

Lateral position　（m）

Left ear signalRight ear signal

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• NoNo dynamic range dynamic range lossloss– Quality (Lossless)Quality (Lossless)– Good S/NGood S/N– No distortionNo distortion

• RobustRobust to errors in plants and filters to errors in plants and filters– Robust to individual difference in HRTFsRobust to individual difference in HRTFs– Generic inverse filtersGeneric inverse filters

• Flat amplitudeFlat amplitude response of inverse filters response of inverse filters– Elevation (height etc) works at any locationElevation (height etc) works at any location– No colouration at any location No colouration at any location

• SmallSmall sound sound radiationradiation other than receiver directions other than receiver directions– Robust to room reflectionsRobust to room reflections

• ConsistentConsistent radiation over frequency radiation over frequency– Multiple listener listeningMultiple listener listening

Aspects of the “OPSODIS”

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3 channel OPSODIS

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Frequency/azimuth

Inverse filter ~ 2 channel OSD

level

-40dB

0dB

2ch OSDIn-phase component

Out-of-phasecomponent

frequency

high

low low

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Frequency/azimuth

Inverse filter ~ 3 channel OSD

level

-40dB

0dB

high

low low

3ch OSD

In-phase component

Out-of-phasecomponent

frequency

high

low low

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Extension to 3 channel

2ch OSD

3ch OSD

In-phase component

Out-of-phasecomponent

2ch

3ch2ch OSD

3ch OSD

Singular values of the inverse filter matrix H

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3 channel OSDfr

eque

ncy

20kHz

0° 180°20Hzvalle

yp

eak

60° 120°

200Hz

2kHz

2ch OSD

2ch OSD

transducer azimuth

excess amplification

peak (out of phase) peak (out of phase) = valley (in phase)= valley (in phase)

3ch OSD

peak (in phase) peak (in phase) = valley (out of phase)= valley (out of phase)

3ch OSD3ch OSD

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Addition

Crosstalk cancellation of 3ch OPSODIS

L

R

CancellationLeft ear

Right ear

Independent control at both ears

C

amplitudephase

Right ear

Left ear

Loudspeaker output

¼ amplitude, -90º phase

½ amplitude

¼ amplitude, +90º phase

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Crosstalk cancellation of 3ch OPSODIS

L

R

Left ear

Right ear

Independent control at both ears

C

amplitudephase

Right ear

Left ear

Loudspeaker output

¼ amplitude, -90º phase

½ amplitude

¼ amplitude, +90º phase

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Crosstalk cancellation of 3ch OPSODIS

L

R

Left ear

Right ear

Independent control at both ears

C

amplitudephaseDestructive interference

Constructive interference

Right ear

Left ear

Loudspeaker output

Efficient, Lossless, Quality, Robust to Efficient, Lossless, Quality, Robust to errors.errors.

¼ amplitude, -90º phase

½ amplitude

¼ amplitude, +90º phase

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Crosstalk cancellation of 3ch OPSODIS

L

R

Left ear

Right ear

Independent control at both ears

C

amplitudephaseDestructive interference

Efficient, Lossless, Quality, Robust to Efficient, Lossless, Quality, Robust to errors.errors.

Right ear

Left ear

Loudspeaker output

Constructive interference

1/3 amplitude, -120º phase

1/3 amplitude

1/3 amplitude, +120º phase

• OPSODISOPSODIS– Enabling high definition 3D sound reproduction with 2 channel (or 3ch)

loudspeakers – Natural sound quality without distortion– Natural sound at any location– Effective in any room– Compatible with surround reproduction

enables ideal 3D sound enables ideal 3D sound delivered to ears.delivered to ears.

SummarySummary

Combination of signal processing Combination of signal processing and the new type of loudspeaker and the new type of loudspeaker based on a new principlebased on a new principle