Ambisonics …

old and new… old and new

Peter Craven

peter@algol.co.uk

Clement Adler Paris Exhibition 1881

1881

Adler

1931

Blumlein

1957

Stereo

LP

1970

quadra-

phonics

2003

„HOA‟

Stereo/Ambisonic timeline

1971

Directional

encoding

patents

(Cooper,

Fellgett)

1975

Ambisonic

Soundfield

microphone

1992

„Vienna‟

decoder

1980

Peri-

Phonic

demo

8th May

1971

Tetrahedral

array

7th Feb

1972

“Spherical mic”

idea

12th July

1974

Patent

filed

1975

Proto-

type

1980+

Commercial

Product

Soundfield mic timeline

8th May 1971

Photo: Stephen Thorntonmichaelgerzonphotos.org.uk

Directional Encoding

Speaker Based Encoding

“I want this sound to come out of the front-left loudspeaker”

“I want this sound to come from 45 deg left of front”

whether there is a loudspeaker there or not

June 1970

Duane H. Cooper 1971

US pat 3,856,992Peter B. Fellgett 1971

British pat 1,369.813

+ -

-

+

+ Omnidirectional

Figure-of-eight

Figure-of-eight

1

cos(θ )

sin(θ )

W

X

Y

W, X, Y Horizontal 1st order Ambisonics

Ambisonic panpot

W

X

Y

cos

sin

x

xθ

WXY encoding

Ambisonic panpot

W

X

Y

cos

sin

x

xθ

Ambisonic mixing

+

+

+ W

X

Y

g1

cos

sin

x

x

g2

cos

sin

x

x

θ1

θ2

Nimbus-Halliday microphone

-

+

+ -+ =

WXY decoding

+

-

α β

X Y

-

+

+ -+ =

WXY decoding

+

-

+

-

+ =+

-

+

+ -+ =

WXY decoding

+

-

+

-

+ =+“Virtual microphone”

+ + + =

+ + =

+ =

Spherical harmonics

W

YX Z

Spherical harmonics

2nd order

U

T

V

R

S

Directional Psychoacoustics

Michael Gerzon 1945-1996

Imaging

• Phantom images

• „Discrete‟ reproduction

• Sound field reconstruction

(animation – Jerôme Daniel)

High Order Ambisonics

“Unfortunately, arguments from information

theory can be used to show that to recreate a

sound field over a two-metre diameter listening

area for frequencies up to 20kHz, one would

need 400,000 channels and loudspeakers. These

would occupy 8GHz of bandwidth, equivalent to

the space used up by 1,000 625-line television

channels!”

Michael Gerzon: “Surround-sound psychoacoustics”

Wireless World, December 1974

www.audiosignal.co.uk

Gerzon‟s approach

• Don‟t rely on a single theory of „how the

ear works‟

• Try to make many cues as possible point

to the correct direction

Conflicting cues cause „listener fatigue‟

Gerzon localisation

AES preprint 3345 section 3

(rv, θv) Velocity vector

(re, θe) Energy vector

x

y

Velocity

x

y

V

Energy

x

y

E

Rhonda Wilson

Meridian Audio

x

y

Velocity Energy

x

y

v

x

y

E

x

y

V

E

AES preprint 3345 section 3

Ambisonics does not work away from the ‘sweet spot’

Ambisonics cannot work away from the ‘sweet spot’

Ambisonics does not work away from the ‘sweet spot’

• If you close your eyes, you can‟t tell where the speakers

are

• Images are not crisp, but they can have a magical

„hanging in space‟ quality

• If you move from the sweet spot, the sound stage moves

with you, as if projected to infinity.

It does not disintegrate or collapse into one speaker.

• Velocity localisation theory assumes coherent addition

• This is pretty well scrambled by 500Hz, even for the

person sitting next to you

• So no point in requiring θv = θe at the „sweet spot‟

Ambisonics cannot work away from the ‘sweet spot’

• Gerzon & Barton “Ambisonic Decoders for HDTV”

AES preprint 3345 (1992)

…..

• Gerzon & Barton “Ambisonic Decoders for HDTV”

AES preprint 3345 (1992)

…..

Thank you

Peter Craven

peter@algol.co.uk