Schoeps-wittek Stereo Surround

November 2008

… Surround Microphones

Surround Microphone Techniques in Practice Demonstration of experimental recordings Helmut Wittek SCHOEPS Mikrofone GmbH Karlsruhe, Germany

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 © J.Wuttke

Compactness

ORTF

CMXY

AB

KFM 6 CMIT-MS

Surround Techniques in general

Compactness

IRT cross

KFM 360

OCT Double MS

Decca Tree

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


• [email protected] ; [email protected]

Sound Sample #1

• OCT Surround – Stadtkirche, Karlsruhe – A-capella amateur choir – Bach motet: Komm, Jesu, komm

DEMO Sound 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?

Spatial impression Direction

0 ms

Distance, Depth, Spaciousness

30 ms

Envelopment Reverberance

t © Theile

Spatial Perception Discrete Signals:

Diffuse Signals:

Correlated at both ears

Decorrelated at both ears

From discrete directions

From all directions

Spatial impression Direction

0 ms

Distance, Depth, Spaciousness

30 ms

Envelopment Reverberance

t © Theile

Directions and points in time Direct Sound s Early Reflections Reverb

0 10 20 30

ms tim e

2.0 Reflection pattern Direct Sound

L

R

Early Reflections Reverb

0 10 • Directional imaging of direct sound and early reflections

• Envelopment, depth?

20 30

ms ti

me • Reflection density too high!
has to be reduced

• Diffuse sound (Reverb) should be reproduced as diffuse as possible
decorrelated!

5.1 Reflection pattern C

Direct Sound

L

R

Early Reflections Reverb

0

10 • Directional imaging of direct sound and early reflections

LS•

Envelopment, depth?

20 30

RS ms

tim e • Reflection density is good, Lateral reflections are important

• Diffuse sound (Reverb) should be reproduced as diffuse as possible
decorrelated!

5.1 Spatial reproduction

Imaging area

C Early reflections

L

R

Reverb

LS

RS

DEMO Sound Sample #2 Sprache IR

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:

L

R

DFC 0

DFC L

R

0.5

Diffuse field correlation (DFC)

DFC L

R

1

Diffuse Field Correlation DFC

• Diffuse Field Correlation DFC of coincident microphone setups:

Setup

DFC ( -1 ... 1 )

XY, 90° 2 Cardioids

XY, 120° 2 Supercardioids

Blumlein, 90° 2 Figure-8

XY, 180° 2 Cardioids

0.75

0.23

0

0.5

Diff_GUI

Diffuse Field Correlation DFC

Correlation vs. microphone angle

ds i o rdi a erc p Su

n Blumlei

Correlation coefficient (DFC)

XY

Offset angle (°)

is n Om

DEMO Sound Sample #3 Laeisz Sprache IR

Diffuse Field Correlation DFC

•

DFC of spaced setups is frequency-dependent Korr_GUI

•

Samples from Laeiszhalle, Hamburg: © Jan Korte – Small AB 52 cm

– Double MS: Supercardioids 120°

Small AB 52 cm

Supercardioids, 120°

Directional Imaging

100%

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” on www.hauptmikrofon.de

D 75%

B A

50%

7,5 % / dB 25%

0

3 6 9 12 15 Interchannel level difference ∆L [dB]

100%

D Phantom source shift

•

Phantom source shift

C

75%

B

A

E 50%

13 % / 0,1ms 25%

0

0,2 0,4 0,6 0,8 1,0 Interchannel time difference ∆t [ms]

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 •

DEMO Sound Sample #4 Showroom

SCHOEPS Microphone Showroom: www.schoeps.de/showroom offers an interactive comparison of stereo techniques…

XY

UMS 20

UMS 20

M100C

CMXY

MS

UMS 20 CMIT MS

CMC 64 + CCM 8

WSR MS

RCY

MS-BLM

SGMSC (CCM4 + CCM8)

ORTF and AB Stereo STCg

Decca 3 * CCM 2H MSTC 64 U, STC

M100C UMS 20

MAB1000 KFM 6

ORTF Outdoor Set

Surround Microphone Design

•

Directional Image: – Image Assistant – Crosstalk: never 3 correlated direct signals!

α = 30°

α = 0°

L, R: C: b: h:

Super-Cardioid Cardioid 40 .... 100 cm 8 cm

OCT setup

C α = 90°

h = 8 cm

L

b = 40 .. 100 cm

R

L CR

Stability in 5.1

Localisation curve on off-centre position

Auslenkung (Grad) ϑ Perceived sourceΦdirection

C

R

Sitzposition LINKS: Lokalisationskurven experimentell

L

•

30 30 15 15 0

0

-15 -15 -30 -30 -60 OCT 70 OCT 70

-30

0

30 60 Sound Einfallswinkel (Grad)source direction Ω INA INA 33

(Mittelwert + 95% Vertrauensbereich)

Quasi-ORTF Quasi-

ORTF

DEMO Sound Sample #5 OCT: Porta Westfalica

OCT Surround Early reflections

OCT Surround

C L

Reverb

R

h

b

40 cm b + 20 cm

RS LS

OCT Surround Setup OCT Surround using 5 SCHOEPS CCM compact microphones and the stereo bar MAB1000

RS Front + 20cm

R

LS 8 cm 40 cm

L

C 40 - 100 cm

DEMO Sound Sample #6 Lyon: OCT SurroundOCT+Hamasaki

OCT + Hamasaki Early reflections

OCT + Hamasaki square

Reverb

C L

R

h b

+-

>2m

+-

L

R

>2m

LS

+-

+-

RS

DEMO Sound Sample #7 Lyon: Decca+HamasakiOCT+Hamasaki

Omni setups / Decca Tree •

Decca Tree

C

h > 0.5 m

L

•

Surround channels: – – –

2 further microphones, 1-4 m apart Hamasaki square etc.

b > 1.5 m

R

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°

DEMO Sound 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

OCT Surround IRT cross

Decca Tree

KFM 360

Double MS: The M/S principle

M=L+R S=L-R

M S

L R

1 L = *( M + S) 2 1 R = *( M -S) 2

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) b)

each pair is decoded separately decoding utilizes the third microphone as well

LR

a) LR

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

DEMO Sound Sample #9 Schostakovitsch Klavierkonzert Rossini

DEMO Sound Sample #10 Schalke Volksmusik 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. 2. 3. 4.

OCT – DMS IRT – DMS ORTF Surround – DMS OCT – Decca Tree – Hamasaki – DMS

OCT Surround

OCT + Hamasaki Decca Tree + Hamasaki

DEMO Sound Sample #11 Porta Westfalica Marktplatz Kammertheater Lyon Marktplatz Schalke Durlach, Altstadtfest

IRT cross

Double MS

ORTF Surround

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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