ambisonics - audio engineering society · stereo/ambisonic timeline 1971 directional encoding...
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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)
…..
