Higher order Ambisonics Higher order Ambisonics A future-proof 3D - - PowerPoint PPT Presentation

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Higher order Ambisonics Higher order Ambisonics A future-proof 3D - - PowerPoint PPT Presentation

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Higher order Ambisonics Higher order Ambisonics A future-proof 3D audio technique A future-proof 3D audio technique What is Ambisonics? What is Ambisonics? How does it work? How does it work? Higher orders: Higher orders: theory and

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Higher order Ambisonics Higher order Ambisonics

A future-proof 3D audio technique A future-proof 3D audio technique

Jörn Nettingsmeier Jörn Nettingsmeier

Meister für Veranstaltungstechnik Meister für Veranstaltungstechnik Essen/Germany Essen/Germany nettings@stackingdwarves.net nettings@stackingdwarves.net http://stackingdwarves.net http://stackingdwarves.net

What is Ambisonics? How does it work? Higher orders: theory and practice Project report What is Ambisonics? How does it work? Higher orders: theory and practice Project report

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Ambisonics is...

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Ambisonics is...

...just a signal representation. It is not equivalent or limited to the sound field microphone.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Ambisonics is...

...just a signal representation. It is not equivalent or limited to the sound field microphone. ...based on the concept of spatial sampling. Just as in temporal sampling, you can scale the sampling density to the desired resolution.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Ambisonics is...

...just a signal representation. It is not equivalent or limited to the sound field microphone. ...based on the concept of spatial sampling. Just as in temporal sampling, you can scale the sampling density to the desired resolution. ...independent of the consumer's speaker layout.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Ambisonics is...

...just a signal representation. It is not equivalent or limited to the sound field microphone. ...based on the concept of spatial sampling. Just as in temporal sampling, you can scale the sampling density to the desired resolution. ...independent of the consumer's speaker layout. ...systematic and mathematically sound, making optimal use

  • f hardware and transmission bandwidth (three channels for

basic horizontal home surround!).

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Also, Ambisonics...

...degrades gracefully when playback capabilities are limited.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Also, Ambisonics...

...degrades gracefully when playback capabilities are limited. ...allows for very reasonable automatic fold-downs to stereo

  • r 5.0.
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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Also, Ambisonics...

...degrades gracefully when playback capabilities are limited. ...allows for very reasonable automatic fold-downs to stereo

  • r 5.0.

...provides perfectly smooth panning, without timbral or focal changes.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Also, Ambisonics...

...degrades gracefully when playback capabilities are limited. ...allows for very reasonable automatic fold-downs to stereo

  • r 5.0.

...provides perfectly smooth panning, without timbral or focal changes. ...is fully isotropic, i.e. it works equally well in all directions.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Also, Ambisonics...

...degrades gracefully when playback capabilities are limited. ...allows for very reasonable automatic fold-downs to stereo

  • r 5.0.

...provides perfectly smooth panning, without timbral or focal changes. ...is fully isotropic, i.e. it works equally well in all directions. ...naturally includes height, without requiring special case panning.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

“If you know the sound pressure and velocity in any point on the surface of a source-free volume, you have complete knowledge of the sound field inside.”

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

“If you know the sound pressure and velocity in any point on the surface of a source-free volume, you have complete knowledge of the sound field inside.” = If you can record the boundary,

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

“If you know the sound pressure and velocity in any point on the surface of a source-free volume, you have complete knowledge of the sound field inside.” you can reproduce the entire inside! = If you can record the boundary,

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

Consider a spherical volume that encloses the listener:

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

If we put an infinite number of mics all over the surface of our sphere...

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

...then use an infinite number of loudspeakers to play back the recorded signal...

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

The Kirchhoff-Helmholtz Integral

...the result will be identical to the

  • riginal performance.
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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sampling the sphere

Microphones can be thought of as spatial sampling instruments. By using their directional characteristics, maybe we can use a finite number of mics and still get good results.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sampling the sphere

So how to approach this in a clever way?

?

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sampling the sphere

The systematic approach: Find a set of polar patterns that cover the sphere uniformly. Avoid redundant information.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sampling the sphere

An omni pattern will sample the sphere completely. No directional information, unfortunately.

W

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sampling the sphere

Three figures-of- eight will also cover the sphere uniformly. Together with W, they provide directional information.

Z Y X

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

an omni in the middle

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

an omni in the middle a fig8 for left-right

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

a fig8 for front-back an omni in the middle a fig8 for left-right

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

works well for horizontal sound

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

Problem: Sound from

  • utside the

horizontal plane arrives at the capsules at different times.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” B-format microphone:

Problem: Sound from

  • utside the

horizontal plane arrives at the capsules at different times. (even worse with an additional Z mic)

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sound field microphone:

three cardioids in the corners of a tetrahedron

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sound field microphone:

three cardioids in the corners of a tetrahedron uniform time errors in all directions

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sound field microphone:

works well when you make the array small

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Sound field microphone:

equivalent to B-format:

LBU

RBD LFD RFU

W = LFD + RFU + LBU + RBD X = LFD + RFU – LBU – RBD Y = LFD – RFU + LBU – RBD Z = - LFD + RFU + LBU - RBD

works because our approach is systematic!

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Decoding B-format

B-format to square layout: LF = W + X + Y RF = W + X – Y LB = W – X + Y RB = W – X – Y

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

B-format to diamond layout: F = W + X L = W + Y R = W - Y B = W – X

Decoding B-format

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Other layouts can be derived using trigonometric functions and gain coefficients.

Decoding B-format

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

5.0 or stereo fold-downs work similarly. Irregular layouts lose some spatial resolution and will introduce slight localisation errors.

Decoding B-format

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

What's wrong with first-order Ambisonics?

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

What's wrong with first-order Ambisonics?

Low angular resolution: shallow off-axis roll-off.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

What's wrong with first-order Ambisonics?

In practice, this means instability and a small sweet spot (= listening area)

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

So we need narrower polar patterns which again sample the sphere uniformly and are linearly independent ...

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

...and here they are:

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Higher-order Ambisonics

0th order 1st 2nd 3rd 4th channels: 1 4 9 16 25

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“Native” higher order microphones do not exist. But we can use the same trick as the tetrahedral mic:

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

And for synthetic sources or spot mics, we can use panning functions that compute higher-order components.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Producing in HOA

Problem: Existing higher-order microphones are not satisfactory for high-quality recording.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Producing in HOA

Problem: Existing higher-order microphones are not satisfactory for high-quality recording. But: There is no satisfying single 7.1, 22.2 or Auro-3D mic either – no problem: we can combine and pan mono sources easily.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Producing in HOA

  • Pop: √
  • Cinema: √
  • Electro-acoustic music: √
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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Producing in HOA

  • Pop: √
  • Cinema: √
  • Electro-acoustic music: √

But how to record classical events?

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Saunders, “Chroma XII” Saunders, “Chroma XII”

→ → Large space (60x10x8m) plus garden Large space (60x10x8m) plus garden → → Musicians on balconies + floor Musicians on balconies + floor → → Audience can move freely Audience can move freely How to capture a walk-around How to capture a walk-around experience? experience?

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

→ → SoundField as main mic: very good SoundField as main mic: very good ambience, but unstable and blurry. ambience, but unstable and blurry. → → Spot mics panned in 3 Spot mics panned in 3rd

rd order, one

  • rder, one

for each(!) instrument: add focus, for each(!) instrument: add focus, allow for balance correction and allow for balance correction and score interpretation. score interpretation.

Hybrid miking approach Hybrid miking approach

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

“ → “ → correct” directional mix, as correct” directional mix, as heard live heard live → → several main mic positions to several main mic positions to allow for change of perspective in allow for change of perspective in post post

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Post-production at IEM Cube, Graz: Post-production at IEM Cube, Graz: 24 Tannoy 1200 24 Tannoy 1200 in a 12-8-4 hemisphere in a 12-8-4 hemisphere

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

5.0 fold-down check 5.0 fold-down check at IEM Produktionsstudio, Graz: at IEM Produktionsstudio, Graz: Genelec ITU 5.1 setup Genelec ITU 5.1 setup 5x 1032a + 1x 1094a 5x 1032a + 1x 1094a No No changes changes in the mix. in the mix.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Concert performance at MUMUTH, Graz: Concert performance at MUMUTH, Graz: 29 Kling & Freitag CA 1001 29 Kling & Freitag CA 1001

  • n motorized
  • n motorized

telescopes plus telescopes plus two sub stacks, two sub stacks, arranged in a arranged in a squashed squashed 12-10-6-1 12-10-6-1 hemisphere hemisphere No changes in the mix. No changes in the mix.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Listening session with composer: Listening session with composer: the SPIRAL system the SPIRAL system at Huddersfield University, at Huddersfield University, 25 Genelec 8240A in three stacked 25 Genelec 8240A in three stacked rings of eight plus zenith, with 4 rings of eight plus zenith, with 4 7270A subs. 7270A subs. No changes in the mix. No changes in the mix.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Thanks for your attention!

I'm looking forward to your questions.

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Tonmeistertagung 2010, Leipzig Jörn Nettingsmeier, http://stackingdwarves.net

Acknowledgements: Polar pattern graphs: Wikimedia Commons Microphone and grand piano clipart:

  • penclipart.org

Spherical harmonics chart: Robin Green, Spherical Harmonic Lighting:The Gritty Details, 2003