… 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

Stereo Techniques in general

CMXYORTF

CMIT-MS

KFM 6

AB

© J.Wuttke

Compactness

Surround Techniques in general

Double MS

IRT cross

OCT

KFM 360

Decca TreeCompactness

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

• wittek@schoeps.de ; surround@schoeps.de

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

s

Directions and points in time

0 10 20 30 ms time

Direct Sound

Early Reflections

Reverb

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!

L RC

LS RS

Early reflections

Reverb

Imaging area

5.1 Spatial reproduction

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

XY

UMS 20 UMS 20

M100C

CMXY

MS

CMIT MS

CMC 64 + CCM 8

RCY

SGMSC(CCM4 + CCM8)

MS-BLM

WSR MS

UMS 20

ORTF and AB Stereo

STCg

MSTC 64 U, STC

M100CUMS 20

KFM 6

MAB1000

ORTF Outdoor Set

Decca3 * CCM 2H

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

IRT cross

• Test recordings

KFM 360 for 5.1 Surround

• 18 cm sphere microphone + 2 * fig-8

• MS processor to produce 5.1 output

Surround – non-coincident

IRT cross

OCT Surround

Decca Tree

KFM 360

Double MS: The M/S principle

R - L S

R L M

=+=

) S - M ( * 2

1 R

) S M ( * 2

1 L

=

+=

M S

LR

The Double M/S idea

• Front M/S pair

• Rear M/S pair

• Combined Double M/S triplet

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

Crosstalk

• Crosstalk in Double M/S

Avoid crosstalk by optimal decoding

4ch 5ch

Film recording

• Double M/S with shotgun

– for live surround e.g. in documentaries

Surround - coincident

CMIT-Double M/S

Double M/S

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.

SCHOEPS Mikrofone

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– 21 capsules

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• Special accessories for every application– Studio, Live, Film, Instrument, Conference, Broadcast, Show, Stereo/Surround, etc.

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