… Surround Microphones
Surround Microphone Techniques in Practice
Demonstration of experimental recordings
Helmut WittekSCHOEPS Mikrofone GmbH
Karlsruhe, Germany
November 2008
Contents
• Overview of applied psychoacoustics
• Practical examination: Sound samples of experimental recordings
• Discussion of popular Surround microphone techniques
Topics
• Practical aspects
• Stereophonic imaging
• Spatial reproduction
• Differences between and pros and cons of the respective microphone setups
More Information
• Get more information and samples:– www.hauptmikrofon.de (Theile, Wittek)
– SCHOEPS Surround brochure
– www.schoeps.de
• This presentation and other in-depth papers
• More info on all setups, applications, topics
• free Double MS-Plug-in (Win/MAC)
• Demo samples
– Contact me
Sound Sample #1
• OCT Surround – Stadtkirche, Karlsruhe
– A-capella amateur choir
– Bach motet: Komm, Jesu, komm
DEMOSound Sample #1
Komm, Jesu, komm
Spatial Perception
• The reference: perception of a natural source
– Where, how distant, in which room, what is the room like?
– What does the source radiate?
t0 ms 30 ms
DirectionDistance,Depth,
Spaciousness
© Theile
EnvelopmentReverberance
Spatial impression
Spatial Perception
t0 ms 30 ms
DirectionDistance,Depth,
Spaciousness
Spatial impression
EnvelopmentReverberance
Discrete Signals:
Correlated at both ears
From discrete directions
Diffuse Signals:
Decorrelated at both ears
From all directions
© Theile
L R
0 10 20 30 ms time
Direct Sound
Early Reflections
Reverb
• Directional imaging of direct sound and early reflections
• Envelopment, depth?
• Reflection density too high! has to be reduced
• Diffuse sound (Reverb) should be reproduced as diffuse as possible decorrelated!
2.0 Reflection pattern
5.1 Reflection pattern
RS
L R
LS
C
0 10 20 30 ms time
Direct Sound
Early Reflections
Reverb
• Directional imaging of direct sound and early reflections
• Envelopment, depth?
• Reflection density is good, Lateral reflections are important
• Diffuse sound (Reverb) should be reproduced as diffuse as possible decorrelated!
Diffuse Field Correlation DFC
Reproduction of the reverb tail:
- Should be diffuse, should be perceived from everywhere
- The more correlation, the narrower the image of the reverb tail and it will get localizable
The diffuse sound should be reproduced decorrelated.
The decisive measure is called:
Diffuse field correlation
(DFC)
L R
L R
L R
DFC
0
0.5
1
DFC
DFC
DEMOSound Sample #2
Sprache IR
• Diffuse Field Correlation DFC of coincident microphone setups:
Diffuse Field Correlation DFC
0
Blumlein,
90°2 Figure-8
XY,
180°2 Cardioids
XY,
120°2 Super-cardioids
XY,
90°2 Cardioids
Setup
0.50.230.75DFC
( -1 ... 1 )
Diff_GUI
Diffuse Field Correlation DFC
Correlation vs. microphone angle
Supercardioids
Cor
rela
tion
coef
ficie
nt (
DF
C)
XYOmnis
Offset angle (°)
Blum
lein
• DFC of spaced setups is frequency-dependent
• Samples from Laeiszhalle, Hamburg:© Jan Korte
– Small AB 52 cm
– Double MS:Supercardioids 120°
Diffuse Field Correlation DFC
Supercardioids, 120°
Small AB 52 cm
Korr_GUI
DEMOSound Sample #3Laeisz Sprache IR
Directional Imaging
• Level and time differences govern the perceived phantom source direction
– φL = f (∆L) ;– φt = f (∆t) ;– φ = φL + φt;
• The necessary interchannel differences are rather similar to those known from natural hearing
• Recording angle
– Recording angle 75%
• “Image Assistant” onwww.hauptmikrofon.de
7,5 % / dB
100%
50%
75%
25%Ph
anto
m s
ou
rce
shif
t
0 3 9 126Interchannel level difference ∆∆∆∆L [dB]
15
A
DC
B
100%
50%
75%
25%Ph
anto
m s
ou
rce
shif
t
0 0,2 0,8 1,00,60,4Interchannel time difference ∆∆∆∆t [ms]
13 % / 0,1ms
B
D
E
A
Principal issues in Microphone Design
• Directional Image:
– can be calculated, differences between stereo techniques regarding the image
• Early reflections:
– Lateral reflections are important – should be perceived separately
• Diffuse Field Reproduction:
– Diffuse Field Correlation DFC should be minimal, can easily be predicted the channels have to be decorrelated regarding the diffuse sound
• Further points of interest:
– Reality is not always ideal!
– Type and properties of single capsules (pressure/pressure gradient transducer)
– Direct/Reverb ratio controls reflection level
– Loudness balance
– Size of the setup
– Sensitivity to wind noise
2-ch setups in practice 1
• AB, Decca Tree– 2-3 * Omni (LF pickup !)
– Distance: 0.5 .. 2 m (decorr!)
– Most popular for orchestra recording
– Vague directional image, open spatial image
– Potentially low DFC and reflection density
• ORTF, quasi-ORTF setups– 2 cardioids (or var.)
– Distance: 0.17 m, Angle: 110 ° (or var.)
– Most popular for ensemble recording
– Good directional image, good spatial image
– Low reflection density, low DFC
2-ch setups in practice 2
• KFM 6 - sphere microphone– 2 Half-Omnis
– Distance: 0.2 m
– Most popular for natural spaces
– Very natural directional and spatial image
– Reflection density and DFC are natural high!
• XY, MS setups– 2 directional pattern or M (variable) + S (fig-8)
– Distance: 0 m, Angle ≥ 90°
– Most popular for film, music, drama recording
– Good directional image, clear spatial image
– Reflection density and DFC strongly depend on the setup
Comparison of stereo setups
• SCHOEPS Microphone Showroom: www.schoeps.de/showroom
offers an interactive comparison of stereo techniques…
DEMOSound Sample #4
Showroom
Surround Microphone Design
• Directional Image:
– Image Assistant
– Crosstalk: never 3 correlated direct signals!
L
h = 8 cm
C
R
L, R: Super-CardioidC: Cardioidb: 40 .... 100 cmh: 8 cm
OCT setup
b = 40 .. 100 cm
L C Rα = 30°α = 0°
α = 90°
Stability in 5.1
• Localisation curve on off-centre position
INA 3OCT 70 Quasi-ORTF
Einfallswinkel (Grad)
Sitzposition LINKS: Lokalisationskurven experimentell
(Mittelwert + 95% Vertrauensbereich)
LC
R
Aus
lenk
ung
(G
rad)
Φ
-60 0 60
-30
30
0
30-30
-15
15
30
15
0
-30
-15
Per
ceiv
edso
urce
dire
ctio
nϑϑ ϑϑ
Sound source direction ΩΩΩΩQuasi-ORTF
INA 3OCT 70
OCT Surround
L h
C
R
OCT Surround
b
b + 20 cm
40 cm
LS
RS
Early reflections
Reverb
DEMOSound Sample #5
OCT: Porta Westfalica
OCT Surround Setup
OCT Surround using 5 SCHOEPS CCM compact microphones and the stereo bar MAB1000
40 cm
Front + 20cm
40 - 100 cm
8 cm
LC
R LS
RS
OCT + Hamasaki
L h
CR
OCT + Hamasaki square
b
> 2 m
LS RS
Early reflections
Reverb
L R
> 2 m
+ -
+ -
+ -
+ -
DEMOSound Sample #6
Lyon: OCT Surround-OCT+Hamasaki
Omni setups / Decca Tree
• Decca Tree
L
h > 0.5 m
C
Rb > 1.5 m
• Surround channels:
– 2 further microphones, 1-4 m apart
– Hamasaki square
– etc.
DEMOSound Sample #7
Lyon: Decca+Hamasaki-OCT+Hamasaki
IRT cross and ORTF Surround
• IRT cross for Surround atmos:
– 4 Cardioids at 20 cm - 90°
– 4 Supercardioids at 14 cm - 90°
• “ORTF Surround” for Surround atmos:
– 4 Supercardioids at 10/20 cm - 100°/80°
IRT cross and ORTF Surround
• IRT cross for Surround atmos
– 4 Cardioids at 20 cm - 90°
– 4 Supercardioids at 14 cm - 90°
• “ORTF Surround” for Surround atmos
– 4 Supercardioids at 10/20 cm - 100°/80°
DEMOSound Sample #8
ORTF Surround/DMS:Durlach Altstadtfest:
Atmo - Kapelle
The Double M/S decoding
Double M/S enables 2 different decoding methods:
a) each pair is decoded separately
b) decoding utilizes the third microphone as well
L R
L R
a)
b)
Tools for Decoding
Decoding variants:
• 2 M/S Matrices
• Hardware (M DMS)
• Software (VST, RTAS)
– Try by yourself, it’s free!
– www.schoeps.de/dmsplugin.htm
DEMOSound Sample #9SchostakovitschKlavierkonzert
Rossini
DEMOSound Sample #10
SchalkeVolksmusik
Drums
What‘s best for …?
1. OCT – DMS
2. IRT – DMS
3. ORTF Surround – DMS
4. OCT – Decca Tree –Hamasaki – DMS
DEMOSound Sample #11Porta Westfalica
MarktplatzKammertheater
LyonMarktplatzSchalke
Durlach, Altstadtfest
OCT Surround
IRT cross
ORTF Surround
Double MS
OCT + Hamasaki
Decca Tree + Hamasaki
What‘s best for …?
• The choice of the recording setup depends on:
– Aesthetical intention of the tonmeister
– Available space on location
– Available time/manpower for the installation (fail-safe)
– Need for wind screen and elastic suspension
– Ease of use, robustness
– Post-production or live broadcast
• Thank you
What does the microphone need?
• The microphone is the basis for all.
• Well-known parameters govern the quality:– Good frequency response
– Smooth polar pattern
– Low noise floor
– Good reliability
– And the sound…
Thank you.
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