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Audio Rendering & Ambisonics
Audio Rendering• A single file format contains complete  (3D?) soundfield data• At the playback end, the system reproduces  ...
Ambisonics• The result of experiments by several  researchers:• Professor Fellgett at University of Reading• Michael Gerzo...
Michael A Gerzon
Michael A Gerzon
Michael A Gerzon• 1945–1996
Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein
Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein• Developed technologies that are still ahead  of thei...
Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein• Developed technologies that are still ahead  of thei...
Ambisonics• Arose out of experiments with four-mic  tetrahedral arrays• Led to the development of the Soundfield  mic• SFM ...
Ambisonic Advantages• Apparent movement of sound source• Ambisonics uses more than just level to provide  localisation cue...
Beyond level-only          localisation• Phase-shift panning: localisation by L/R phase  relationships
Ambisonic Advantages• In Ambisonics, each location has its own  combination of level and phase  relationships.• Head Relat...
Soundfield Microphone     Principles• Mid-Side recording  captures a stereo  stage (with a good  sense of depth)• Omni (L+R...
Soundfield Microphone     Principles• SFM extends this into  three dimensions• Omni (sum of all  directions) “W”• Three figu...
Soundfield Microphone    Capsule Array• Tetrahedral array of  capsules as close as  possible• Circuitry for coincidence  co...
Other SFM Designs• Tetramic from Core Sound  …and several others
A-format to B-format• Capsule signals  converted to sum &  difference signals
B-Format:   The Studio Format• W = Left + Right + Front + Back       (+ Up + Down)• X = Front – Back• Y = Left – Right• Z ...
Halliday/Nimbus        mic array• Generates B-Format  directly• Omni and two  figure-8 mics
Transmission• B-Format thought not suitable for  transmission as it is not stereo-compatible.• Is this still a valid probl...
Ambisonics• Two original methods of  transmission:
Ambisonics• Two original methods of  transmission: • B-Format (the studio    format):    sum & difference channels.
Ambisonics• Two original methods of  transmission: • B-Format (the studio    format):    sum & difference channels. • UHJ ...
2-channel Transmission• Matrixing system based on UD-4• BBC Matrix H, HJ• UHJ (“Universal HJ”)• Convert B-Format into a 2-...
2-Channel Decoder• Requires the  listener to have a  decoder at home• One more item to  buy – probably not  supplied with ...
Benefits ofPlayback-end decoding• One single source (disc, file etc) the same  for all applications• Decoder is configured fo...
Disadvantages ofPlayback-end decoding• Decoders are needed ‘out there’.• People have to use them, and set them up  correct...
The Other Side       of Ambisonics• Ambisonics was conceived originally as a  method of accurately capturing and  reproduc...
The Misconception• “Ambisonics requires recording with   a special microphone/array.”
The Misconception• Almost no commercial music can be picked  up live with a single microphone• So what use is Ambisonics?•...
Ambisonic Mixing
Ambisonic Mixing• The vast majority of  popular music is mixed  from multitrack.
Ambisonic Mixing• The vast majority of  popular music is mixed  from multitrack.• Ambisonic panpots predate  the Soundfield...
Ambisonic Mixing• The vast majority of  popular music is mixed  from multitrack.• Ambisonic panpots predate  the Soundfield...
Ambisonics is           good at…• Ambisonics specialises in accurate  localisation• Suggests that if you take care of  loc...
Ambisonic Mixing:       Principles• Multitrack environment• Conventional recording techniques  (may add an SFM if helpful)...
Ambisonic Mixing:      Principles• Mono/stereo sources• B-Format panpots• B-Format bus• Record the mix (3- or 4-channel B-...
Ambisonic Mixing        System• Ambisonic  Mixing System  designed to  allow  conventional  consoles to do  Ambisonics
Ambisonic Mixing System
Ambisonic Mixing Today:   DAW Support• DAW needs to have true multichannel  architecture – not all do!• Most popular:  Ste...
DAW Plug-ins       for Ambisonics• Panners, decoders, reverb etc  implemented as plug-ins• VST is the most popular• Audio ...
Some DAW Plug-ins  for Ambisonics• Daniel Courville’s B2X suite (Mac only)• University of York (Mac/Win)• Gerzonic (Bidule...
Some Current Tools• Daniel  Courville’s  B2X• Apple Audio  Unit and VST  plugins
Some Current Tools• Swiss Centre for  Computer Music• VST plugins
Some Current Tools• University of York• VST Plugins• Also higher-order designs
Future Tools?• Manipulate sounds in  3D space in a virtual  world?
Ambisonic Application:  Large-scale PA• Funktion One:  Tony Andrews• Chemical Brothers,  Glastonbury Festival• London’s Mi...
Replay & Monitoring     Observations• Goal: Wide, accurate listening area  (or a wide area with a good experience).• Ideal...
Degrees of Freedom• Position virtual sources at any angle around  the listener (including height)• Position sounds at a di...
Artistic Freedom• Some people feel that direct virtual sources   should occupy the front stage and only   ambience behind ...
Surround Sound offers:• More freedom to create a sonic  environment for the listener• A more immersive experience• More li...
Ambisonics offers:• Better efficiency than 5.1, 7.1, 10.2 etc• More accurate rendering of source position• Side and rear im...
If Ambisonics is so       wonderful…• Why isn’t everyone using it?• The old stories…• Public Domain!• A lot of people are…...
Ambisonic Recordings www.ambsonia.com
More Resourcesat ambisonic.net
Ambisonics Today• Ambisonics has never been as accessible• Most tools are free• You can develop your own• But what about r...
Spatial Sound 3: Audio Rendering and Ambisonics
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Spatial Sound 3: Audio Rendering and Ambisonics

Part 3 of a series of four presentations that formed the basis of my short course on spatial audio for artists at the Music Department, Ionian University, Corfu, July 2008

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Spatial Sound 3: Audio Rendering and Ambisonics

  1. 1. Audio Rendering & Ambisonics
  2. 2. Audio Rendering• A single file format contains complete (3D?) soundfield data• At the playback end, the system reproduces it to the best of its ability• Analogous to a Postscript file/printer.• No 1:1 channel:speaker mapping• Ambisonics is an example
  3. 3. Ambisonics• The result of experiments by several researchers:• Professor Fellgett at University of Reading• Michael Gerzon, Mathematical Institute, Oxford• and others
  4. 4. Michael A Gerzon
  5. 5. Michael A Gerzon
  6. 6. Michael A Gerzon• 1945–1996
  7. 7. Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein
  8. 8. Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein• Developed technologies that are still ahead of their time:
  9. 9. Michael A Gerzon• 1945–1996• A true genius, at the level of Blumlein• Developed technologies that are still ahead of their time: • Ambisonics; lossless digital coding; etc
  10. 10. Ambisonics• Arose out of experiments with four-mic tetrahedral arrays• Led to the development of the Soundfield mic• SFM extends Blumlein into 3D
  11. 11. Ambisonic Advantages• Apparent movement of sound source• Ambisonics uses more than just level to provide localisation cues – listener position independent
  12. 12. Beyond level-only localisation• Phase-shift panning: localisation by L/R phase relationships
  13. 13. Ambisonic Advantages• In Ambisonics, each location has its own combination of level and phase relationships.• Head Related Transfer Functions (HRTF) are not considered.• Decoder is configured to match the speaker array in the room – original design goal.
  14. 14. Soundfield Microphone Principles• Mid-Side recording captures a stereo stage (with a good sense of depth)• Omni (L+R) and figure-8 (L-R)
  15. 15. Soundfield Microphone Principles• SFM extends this into three dimensions• Omni (sum of all directions) “W”• Three figure-8s at right angles “X”, “Y”, “Z”
  16. 16. Soundfield Microphone Capsule Array• Tetrahedral array of capsules as close as possible• Circuitry for coincidence compensation• Coincident up to about Original 10kHz SFM Design
  17. 17. Other SFM Designs• Tetramic from Core Sound …and several others
  18. 18. A-format to B-format• Capsule signals converted to sum & difference signals
  19. 19. B-Format: The Studio Format• W = Left + Right + Front + Back (+ Up + Down)• X = Front – Back• Y = Left – Right• Z = Up – Down
  20. 20. Halliday/Nimbus mic array• Generates B-Format directly• Omni and two figure-8 mics
  21. 21. Transmission• B-Format thought not suitable for transmission as it is not stereo-compatible.• Is this still a valid problem?• Could B-Format be carried on DVD? BRD?
  22. 22. Ambisonics• Two original methods of transmission:
  23. 23. Ambisonics• Two original methods of transmission: • B-Format (the studio format): sum & difference channels.
  24. 24. Ambisonics• Two original methods of transmission: • B-Format (the studio format): sum & difference channels. • UHJ stereo-compatible matrix: (typically 2-channel UHJ).
  25. 25. 2-channel Transmission• Matrixing system based on UD-4• BBC Matrix H, HJ• UHJ (“Universal HJ”)• Convert B-Format into a 2-channel format• Stereo/mono compatible• Decode at the listening end to suit room
  26. 26. 2-Channel Decoder• Requires the listener to have a decoder at home• One more item to buy – probably not supplied with the audio system
  27. 27. Benefits ofPlayback-end decoding• One single source (disc, file etc) the same for all applications• Decoder is configured for the playback environment: • Number and position of speakers etc
  28. 28. Disadvantages ofPlayback-end decoding• Decoders are needed ‘out there’.• People have to use them, and set them up correctly.• May be easier with software-based playback systems.
  29. 29. The Other Side of Ambisonics• Ambisonics was conceived originally as a method of accurately capturing and reproducing a natural acoustic event.
  30. 30. The Misconception• “Ambisonics requires recording with a special microphone/array.”
  31. 31. The Misconception• Almost no commercial music can be picked up live with a single microphone• So what use is Ambisonics?• Luckily, there are other methods besides a special microphone.
  32. 32. Ambisonic Mixing
  33. 33. Ambisonic Mixing• The vast majority of popular music is mixed from multitrack.
  34. 34. Ambisonic Mixing• The vast majority of popular music is mixed from multitrack.• Ambisonic panpots predate the Soundfield Microphone
  35. 35. Ambisonic Mixing• The vast majority of popular music is mixed from multitrack.• Ambisonic panpots predate the Soundfield Microphone• Ambisonics is particularly good at this: for example, it’s isotropic.
  36. 36. Ambisonics is good at…• Ambisonics specialises in accurate localisation• Suggests that if you take care of localisation, envelopment will take care of itself.• Is this true?
  37. 37. Ambisonic Mixing: Principles• Multitrack environment• Conventional recording techniques (may add an SFM if helpful)• Ambisonics is used at the Mixing stage
  38. 38. Ambisonic Mixing: Principles• Mono/stereo sources• B-Format panpots• B-Format bus• Record the mix (3- or 4-channel B-Format)• Monitor the mix (decoder fed by B-format bus)
  39. 39. Ambisonic Mixing System• Ambisonic Mixing System designed to allow conventional consoles to do Ambisonics
  40. 40. Ambisonic Mixing System
  41. 41. Ambisonic Mixing Today: DAW Support• DAW needs to have true multichannel architecture – not all do!• Most popular: Steinberg Cubase & Nuendo (VST); Apple Logic Pro & Soundtrack Pro 2 (AU); Audio Mulch & Plogue Bidule (VST)• Pro Tools is NOT (really) supported
  42. 42. DAW Plug-ins for Ambisonics• Panners, decoders, reverb etc implemented as plug-ins• VST is the most popular• Audio Units (Apple) also available (B2X)• First Order Ambisonics recommended (higher orders also available)
  43. 43. Some DAW Plug-ins for Ambisonics• Daniel Courville’s B2X suite (Mac only)• University of York (Mac/Win)• Gerzonic (Bidule/Audiomulch)• Bruce Wiggins (Reverb)• Swiss Centre for Computer Music (Max/MSP)• Visual Virtual Microphone
  44. 44. Some Current Tools• Daniel Courville’s B2X• Apple Audio Unit and VST plugins
  45. 45. Some Current Tools• Swiss Centre for Computer Music• VST plugins
  46. 46. Some Current Tools• University of York• VST Plugins• Also higher-order designs
  47. 47. Future Tools?• Manipulate sounds in 3D space in a virtual world?
  48. 48. Ambisonic Application: Large-scale PA• Funktion One: Tony Andrews• Chemical Brothers, Glastonbury Festival• London’s Millennium Dome central show• Sancho Panza at the Glade Festival
  49. 49. Replay & Monitoring Observations• Goal: Wide, accurate listening area (or a wide area with a good experience).• Ideally all speakers are the same.• Ideally all speakers are full range.• Speakers should have wide dispersion.• To a point, more speakers are better (decoder must support them).
  50. 50. Degrees of Freedom• Position virtual sources at any angle around the listener (including height)• Position sounds at a distance with radius vector, level and reverb combinations• Sounds can be stationary or move• Create a complete synthetic soundfield, either like or unlike reality
  51. 51. Artistic Freedom• Some people feel that direct virtual sources should occupy the front stage and only ambience behind the listener – NO!• Place sounds anywhere that you think is valid (including the above).• Mix of a live concert might be like the above; in the studio, anything goes.• If it sounds right, it is right.
  52. 52. Surround Sound offers:• More freedom to create a sonic environment for the listener• A more immersive experience• More listener involvement• Re-creating a real acoustic space/ performance• Creating virtual acoustic spaces
  53. 53. Ambisonics offers:• Better efficiency than 5.1, 7.1, 10.2 etc• More accurate rendering of source position• Side and rear images (and height)• Device-independent rendering: image quality is a function of the replay system• Replay system to suit the environment
  54. 54. If Ambisonics is so wonderful…• Why isn’t everyone using it?• The old stories…• Public Domain!• A lot of people are…• Free tools and systems• Some development needed (Pro Tools etc)
  55. 55. Ambisonic Recordings www.ambsonia.com
  56. 56. More Resourcesat ambisonic.net
  57. 57. Ambisonics Today• Ambisonics has never been as accessible• Most tools are free• You can develop your own• But what about replay on existing surround systems – eg 5.1 home theatre?

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