H.Wittek: Systems and techniques for 3D recording Slide 1

Recording with height

Systems and Techniques

for 3D recording

Helmut Wittek, SCHOEPS GmbH

wittek@schoeps.de

H.Wittek: Systems and techniques for 3D recording Slide 2

Outline

• What is 3D Audio?

– 3D Video � 3D Audio

– 3D Audio-Formats

• Physical/Perceptual effect of the height loudspeakers

• Spatial properties (Direction, Distance, Room) of 3D audio

• Consequences for microphone recording

H.Wittek: Systems and techniques for 3D recording Slide 3

What is 3D-Audio?

• What is 3D-Audio?

• 2D Video:– no real depth, but width + height

3D Video adds the real depth dimension

• 2D Audio:– no height, but width + depth

3D Audio adds the height dimension

• One example for 3D Audio is Multichannel Stereo + height …

H.Wittek: Systems and techniques for 3D recording Slide 4

Multichannel + height

ITU 5.1

= X

= X = X

= X

= X

ITU 5.1

= X

= X = X

= X

= X

• 5.1 Surround + n height channels

– one of the proposals: “Auro3D 9.1” = 5.1 Surround + 4 height channels

30°

H.Wittek: Systems and techniques for 3D recording Slide 5

Potential 3D Audio formats

Sound field synthesis

Reconstruction of the original wave field at the listener’s ears

Stereophony

Creation of a quasi-natural acoustical perception

Ambisonics / HOA

WFS / Derivatives+ height

Binaural

Stereo + height

H.Wittek: Systems and techniques for 3D recording Slide 6

Effect of the height loudspeakers

• 4 main physical changes of the sound field after adding

height loudspeakers:

R CRS5.1:

R CRS

RhRSh

Auro-3D:

R2.0:

R CRS5.1:

R CRS

RhRSh

Auro-3D:

R2.0:

1. More possible directions for

discrete sources

2. More possible directions for

reflections

3. Lower source/reflection

density

4. Higher diffuseness of the

diffuse portions, more evenly

distributed diffuse field

H.Wittek: Systems and techniques for 3D recording Slide 7

Effect of the height loudspeakers

• Hypothesis: 4 main perceptual changes of the sound field after

adding height loudspeakers:

R CRS5.1:

R CRS

RhRSh

Auro-3D:

R2.0:

R CRS5.1:

R CRS

RhRSh

Auro-3D:

R2.0:

1. Enhanced distribution of

sound sources

2. More natural perception of

distance/depth

3. Less coloration

4. More natural spatial

impression; larger diffuse field

sweet spot

H.Wittek: Systems and techniques for 3D recording Slide 8

Properties of 3D Audio

1. Directional Imaging:

• Discrete sources in the height loudspeakers are possible

• Elevation is hardly possible or unstable, coloration is likely

• Up/Down Panning can be used, but it does not create stable phantom

sources, coloration is likely?

• “Filling the area” is possible � a/b technique

• Sufficient channel separation is mandatory for directional imaging

2,2 ms1,7 ms

0,7 ms1,2 ms

∆∆∆∆ t

0,2 ms

3 m 0,6 m

2,2 ms1,7 ms

0,7 ms1,2 ms

∆∆∆∆ t

0,2 ms

3 m 0,6 m

2,2 ms1,7 ms

0,7 ms1,2 ms

∆∆∆∆ t

0,2 ms

3 m 0,6 m

H.Wittek: Systems and techniques for 3D recording Slide 9

Properties of 3D Audio

2. Distance/Depth:

– More natural distance/depth perception?

– Less coloration due to lower reflection density?

3. Spatial impression/Envelopment:

- More natural spatial impression?

- Larger diffuse field sweet spot?

H.Wittek: Systems and techniques for 3D recording Slide 10

Recording for 3D Audio

• Consequences for the recording technique:

– Directional Imaging:

• Stereophonic rules (∆L, ∆t) apply in general for all loudspeaker pairs, height loudspeakers are potentially displaced by 1-2 ms!

– Channel separation:

• discrete signals: one signal on more than two loudspeakers leads to coloration

• diffuse signals: the more de-correlated diffuse sources, the more diffuse is the resulting sound field

H.Wittek: Systems and techniques for 3D recording Slide 11

Two examples for Auro3D recording techniques

• ORTF-like recording techniques, e.g. “OCT 9”

– Closely spaced, directive microphones

– Typical properties:

• proportional and clear directional imaging

• natural spatial impression

– Application: chamber music, drama, sports, ambience

• Wide a/b-like recording techniques

– Widely spaced, omni-directional microphones

– Typical properties:

• stable, but not proportional directional imaging

• enhanced spatial impression

– Application: music, film music

H.Wittek: Systems and techniques for 3D recording Slide 12

Two examples for Auro3D recording techniques

OCT 70 + 4 super-cardioids pointing upwards

msLargely-spaced 9-channel A/B setup

ms

OCT 70 + 4 super-cardioids pointing upwards

msmsLargely-spaced 9-channel A/B setup

msms

Reflection patterns in the “Sweet Spot” of an Auro-3D speaker array, generated using 2 different microphone arrays. The microphone arrays record the same source. A shoebox-shaped recording room was produced for emulation purposes. The source produces a Dirac impulse. Each peak color corresponds to a (1st order) image source.

H.Wittek: Systems and techniques for 3D recording Slide 13

Two examples for Auro3D recording techniques

L h R

lower plane: OCT Surround

upper plane: height + 100cm, 4 Supercardioids pointing upwards

b

b + 20 cm

40 cm

LS RS

C

„OCT 9“:

Lh Rh

LSh RSh

H.Wittek: Systems and techniques for 3D recording Slide 14

Two examples for Auro3D recording techniques

Wide a/b:spacings > 0.5-2 m, upper plane: height + > 1 m

C

L R

LS RS

LS RS

L R

H.Wittek: Systems and techniques for 3D recording Slide 15

Test recordings Galaxy Studio

• Test recordings in Galaxy Studios and HfM Detmold(ICSA):

– OCT 9

– Omni array

Listen to a/b

comparisons -

without/with height

- OCT/Omnis

Workshop WC 5

Today, 14h in the “großerSeminarraum” Thank you!

Questions and corrections are welcome