General-purpose Ambisonic playback systems for electroacoustic - - PowerPoint PPT Presentation

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General-purpose Ambisonic playback systems for electroacoustic - - PowerPoint PPT Presentation

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2 nd International Symposium on Ambisonics and Spherical Acoustics, IRCAM, Paris/France General-purpose Ambisonic playback systems for electroacoustic concerts A practical approach Jrn Nettingsmeier freelance audio and event engineer

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2nd International Symposium on Ambisonics and Spherical Acoustics, IRCAM, Paris/France

General-purpose Ambisonic playback systems for electroacoustic concerts A practical approach

Jörn Nettingsmeier freelance audio and event engineer nettings@stackingdwarves.net http://stackingdwarves.net

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So you are organizing a concert with contemporary electro-acoustic works? Great! Let's publish that call for music, and wait for contributions.

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Hmm. This quadraphonic piece would fit right in!

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Hmm. This quadraphonic piece would fit right in! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1!

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Hmm. This quadraphonic piece would fit right in! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! We got to have this one. Oops – eight speakers at irregular angles and distances?

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Hmm. This quadraphonic piece would fit right in! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! Whee! This one needs six speakers in a regular hexagon. We got to have this one. Oops – eight speakers at irregular angles?

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Hmm. This quadraphonic piece would fit right in! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! This is great, too. Oh, it's 5.1! We got to have this one. Oops – eight speakers at irregular angles? Whee! This one needs six speakers in a regular hexagon. Two speakers in the front, and one in the back? Well...

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Half the show we'll be watching the crew move speakers around...

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Wish I had „virtual speakers“!

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...

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A Higher-order Ambisonic system lets you create virtual speaker positions with reasonable accuracy, to help accommodate a wide range

  • f required speaker layouts.

...well, you do!

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A Higher-order Ambisonic system lets you create virtual speaker positions with reasonable accuracy, to help accommodate a wide range

  • f required speaker layouts.

It also scales nicely to include height.

...well, you do!

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A Higher-order Ambisonic system lets you create virtual speaker positions with reasonable accuracy, to help accommodate a wide range

  • f required speaker layouts.

It also scales nicely to include height. (And as a bonus, you will be able to reproduce native Ambisonic compositions at their very best.)

...well, you do!

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Components:

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Components:

A speaker array suitable for 3rd-order Ambisonic reproduction (horizontal-only here, for the sake of simplicity) A speaker array suitable for 3rd-order Ambisonic reproduction (horizontal-only here, for the sake of simplicity)

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Components:

A Linux rendering PC (or MacOS, or maybe even Windows), with ADAT I/O, using free software A Linux rendering PC (or MacOS, or maybe even Windows), with ADAT I/O, using free software

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Components:

(optionally) a digital mixer, for convenience and safety, with additional ADAT I/O (optionally) a digital mixer, for convenience and safety, with additional ADAT I/O

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Components:

You can do without, but consider this: If your PC gets stuck („motorboating“) or there is a sync problem, you'll get loud digital noise, and no means to turn it off. You can do without, but consider this: If your PC gets stuck („motorboating“) or there is a sync problem, you'll get loud digital noise, and no means to turn it off.

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Components:

That means you're utterly hosed. That means you're utterly hosed.

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Components:

So don't be cheap, get that mixer. So don't be cheap, get that mixer.

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Virtual speakers:

Inside the PC, Ambisonic encoders (a.k.a. panners) will take the discrete input signals, position them at azimuth and elevation angles

  • f your choice,

and route them to a third-order Ambi master bus. Inside the PC, Ambisonic encoders (a.k.a. panners) will take the discrete input signals, position them at azimuth and elevation angles

  • f your choice,

and route them to a third-order Ambi master bus.

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Virtual speakers:

An Ambisonic decoder will then generate speaker signals for the physical speaker layout you have chosen. An Ambisonic decoder will then generate speaker signals for the physical speaker layout you have chosen.

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Virtual speakers:

The speaker signals are routed back through the mixer, where you can calibrate each one for equal loudness, and control the master volume. The speaker signals are routed back through the mixer, where you can calibrate each one for equal loudness, and control the master volume.

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Process different sources:

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Process different sources:

„tape pieces“ from harddisk „tape pieces“ from harddisk

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Process different sources:

live electronics or microphones live electronics or microphones

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Process different sources:

artist-supplied ADAT signals (for material rendered in real-time) artist-supplied ADAT signals (for material rendered in real-time)

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The software stack:

  • Ambisonic encoding: AMB plugin set

(LADSPA, by Fons Adriaensen)

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The software stack:

  • Ambisonic encoding: AMB plugin set

(LADSPA, by Fons Adriaensen)

  • Hosting of plugins, signal routing, tape playback:

Ardour 2.8 (Paul Davis et al., native on Linux and MacOSX)

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The software stack:

  • Ambisonic encoding: AMB plugin set

(LADSPA, by Fons Adriaensen et al.)

  • Hosting of plugins, signal routing, tape playback:

Ardour 2.8 (Paul Davis et al., native on Linux and MacOSX)

  • Ambisonic decoding: AmbDec

(Fons Adriaensen)

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The software stack:

  • Ambisonic encoding: AMB plugin set

(LADSPA, by Fons Adriaensen et al.)

  • Hosting of plugins, signal routing, tape playback:

Ardour 2.8 (Paul Davis et al., native on Linux and MacOSX)

  • Ambisonic decoding: AmbDec

(Fons Adriaensen)

  • Putting it all together: JACK Audio Connection Kit

(Davis, Letz, Hohn et al.)

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Mission control: Mission control:

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Mission control: Mission control: AMB plugins in Ardour AMB plugins in Ardour

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Mission control: Mission control: AMB panners in Ardour AMB panners in Ardour Panners accessible via generic MIDI control surface Panners accessible via generic MIDI control surface

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Mission control: Mission control: AMB panners in Ardour AMB panners in Ardour Panners accessible via generic MIDI control surface Panners accessible via generic MIDI control surface Ganged output faders for volume adjustment;

  • ptionally ganged EQ for tone correction.

Ganged output faders for volume adjustment;

  • ptionally ganged EQ for tone correction.
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The paper contains detailed setup information.

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Advantages:

  • Accommodate arbitrary speaker layout

requirements

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Advantages:

  • Accommodate arbitrary speaker layout

requirements

  • Improve the concert experience by avoiding

disruptive speaker rearrangement breaks

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Advantages:

  • Accommodate arbitrary speaker layout

requirements

  • Improve the concert experience by avoiding

disruptive speaker rearrangement breaks

  • No errors and malfunctions caused by in-flight

rewiring and reconfiguration

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Advantages:

  • Accommodate arbitrary speaker layout

requirements

  • Improve the concert experience by avoiding

disruptive speaker rearrangement breaks

  • No errors and malfunctions caused by in-flight

rewiring and reconfiguration

  • Provide the performer with positional control,

as an additional degree of freedom in sound diffusion

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So where's the catch?

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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
  • On-speaker sources will become slightly more blurred.
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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
  • On-speaker sources will become slightly more blurred.
  • Phantom sources will generally improve.
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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
  • On-speaker sources will become slightly more blurred.
  • Phantom sources will generally improve.
  • Source localisation will be at constant angles, not

absolute positions (watch that center signal when you're doing video-related sound).

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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
  • On-speaker sources will become slightly more blurred.
  • Phantom sources will generally improve.
  • Source localisation will be at constant angles, not

absolute positions (watch that center signal when you're doing video-related sound).

  • Acoustically dry venues will emphasize HF phasing

effects which must be corrected by other means.

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So where's the catch?

  • We introduce artefacts and change some features
  • f the reproduced sound field:
  • On-speaker sources will become slightly more blurred.
  • Phantom sources will generally improve.
  • Source localisation will be at constant angles, not

absolute positions (watch that center signal when you're doing video-related sound).

  • Acoustically dry venues will emphasize HF phasing

effects which must be corrected by other means.

  • Signals susceptible to comb-filtering may suffer.
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So where's the catch?

Artefacts may have different effects and severity, depending on the compositional approach.

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So where's the catch?

While artefacts may be evident in A/B comparison, they need not pose a problem in actual practice.

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Genres unsuitable for Ambi playback:

  • Acousmatic works (a.k.a. music for „Loudspeaker

Orchestra“)

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Genres unsuitable for Ambi playback:

  • Acousmatic works (a.k.a. music for „Loudspeaker

Orchestra“)

  • Pathological signals with large amounts of

negative correlation

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Genres unsuitable for Ambi playback:

  • Acousmatic works (a.k.a. music for „Loudspeaker

Orchestra“)

  • Pathological signals with large amounts of

negative correlation

  • The dialogue channel(s) of movie sound tracks

(workaround: use a discrete speaker for the center)

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Practical experience

  • Past deployments of Ambisonic concert systems

have met with general approval, both by audience and performers:

  • LAC 2009 concert system, Audiorium Paganini, Parma

Eight full-range QSC speakers driven in 3

rd order,

implemented by Fons Adriaensen

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Practical experience

  • Past deployments of Ambisonic concert systems

have met with general approval, both by audience and performers:

  • LAC 2009 concert system, Audiorium Paganini, Parma

Eight full-range QSC speakers driven in 3

rd order,

implemented by Fons Adriaensen

  • DEGEM 2009 concert system, musikFabrik, Köln

Twelve K+H O108TV speakers driven in 3

rd order, plus

two Genelec subs driven with W/Y, implemented by the author

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Practical experience

  • Past deployments of Ambisonic concert systems

have met with general approval, both by audience and performers:

  • LAC 2009 concert system, Audiorium Paganini, Parma

Eight full-range QSC speakers driven in 3rd order, implemented by Fons Adriaensen

  • DEGEM 2009 concert system, musikFabrik, Köln

Twelve K+H O108TV speakers driven in 3rd order, plus two Genelec subs driven with W/Y, implemented by the author

  • CCRMA lecturer Fernando Lopez-Lezcano has reported

very pleasant results in several concerts (one open-air) with a similar eight-channel 3rd order rig

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Listening tests

Practical deployments were always successful. But how does the system fare in a direct A/B comparison?

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Listening tests

  • Two informal listening tests have been conducted

in spring 2010:

  • Kunsthochschule für Medien, Köln, with film and media

artists, using direct A/B comparisons between interspersed 5.0 and 3rd-order horizontal Ambisonics rigs

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Listening tests

  • Two informal listening tests have been conducted

in spring 2010:

  • Kunsthochschule für Medien, Köln, with film and media

artists, using direct A/B comparisons between interspersed 5.0 and 3rd-order horizontal Ambisonics rigs

  • ICEM, Folkwang Universität der Künste Essen, with

electronic composers, using a 3rd-order horizontal rig, A/B-ing between Ambi and quad reproduction

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Listening tests

Test setup: 5.0 or 4.0 content was played back over a virtual Ambisonic rig in 3rd order, and compared with native reproduction over 5 and 4 speakers. Evil! It is clear that Ambi can't outperform the original. Rather, it will combine the defects of both discrete and Ambisonic playback. Does it work? Is it a good compromise?

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Listening tests – film artists

  • absolute position of C is mandatory
  • focus and stability over correctness and

homogeneity

  • no advantage in coverage area
  • phasing artefacts evident in typical cinema

acoustics For film, not too impressed. For music, ok.

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Listening tests – Film artists

Conjecture: Does Ambisonic listening require training or habituation? If so, maybe their verdict would improve over time? But also: can it be that „us Ambi professionals“ routinely over-estimate the impact on casual (i.e. non-habituated) listeners?

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Listening tests – Electronic composers

  • shortcomings inobtrusive
  • often no clear preference (very good!), but large

individual deviations

  • no advantage in coverage area
  • subjects prefer being able to pinpoint speaker

locations over homogeneity

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„In the context of electro-acoustic music, any reproduction is interpretation. Ambisonic reproduction is a valid form of interpretation (except for a few very particular works).“

  • a test participant
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Thank you for your attention!

I'll be happy to address your questions.

2nd International Symposium on Ambisonics and Spherical Acoustics – IRCAM, Paris/France Ambisonic playback systems – Jörn Nettingsmeier <nettings@stackingdwarves.net>