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

1. Audio Rendering
& Ambisonics

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. Ambisonics
• The result of experiments by several
researchers:
• Professor Fellgett at University of Reading
• Michael Gerzon, Mathematical Institute,
Oxford
• and others

4. Michael A Gerzon

5. Michael A Gerzon

6. Michael A Gerzon
• 1945–1996

7. Michael A Gerzon
• 1945–1996
• A true genius, at the level of Blumlein

8. Michael A Gerzon
• 1945–1996
• A true genius, at the level of Blumlein
• Developed technologies that are still ahead
of their time:

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. Ambisonics
• Arose out of experiments with four-mic
tetrahedral arrays
• Led to the development of the Soundfield
mic
• SFM extends Blumlein into 3D

11. Ambisonic Advantages
• Apparent movement of sound source
• Ambisonics uses more than just level to provide
localisation cues – listener position independent

12. Beyond level-only
localisation
• Phase-shift panning: localisation by L/R phase
relationships

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. 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. 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. 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. Other SFM Designs
• Tetramic from Core Sound
…and several others

18. A-format to B-format
• Capsule signals
converted to sum &
difference signals

19. B-Format:
The Studio Format
• W = Left + Right + Front + Back
(+ Up + Down)
• X = Front – Back
• Y = Left – Right
• Z = Up – Down

20. Halliday/Nimbus
mic array
• Generates B-Format
directly
• Omni and two
figure-8 mics

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. Ambisonics
• Two original methods of
transmission:

23. Ambisonics
• Two original methods of
transmission:
• B-Format (the studio
format):
sum & difference channels.

24. Ambisonics
• Two original methods of
transmission:
• B-Format (the studio
format):
sum & difference channels.
• UHJ stereo-compatible
matrix:
(typically 2-channel UHJ).

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. 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. Benefits of
Playback-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. Disadvantages of
Playback-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. The Other Side
of Ambisonics
• Ambisonics was conceived originally as a
method of accurately capturing and
reproducing a natural acoustic event.

30. The Misconception
• “Ambisonics requires recording with
a special microphone/array.”

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. Ambisonic Mixing

33. Ambisonic Mixing
• The vast majority of
popular music is mixed
from multitrack.

34. Ambisonic Mixing
• The vast majority of
popular music is mixed
from multitrack.
• Ambisonic panpots predate
the Soundfield Microphone

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. 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. Ambisonic Mixing:
Principles
• Multitrack environment
• Conventional recording techniques
(may add an SFM if helpful)
• Ambisonics is used at the Mixing stage

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. Ambisonic Mixing
System
• Ambisonic
Mixing System
designed to
allow
conventional
consoles to do
Ambisonics

40. Ambisonic Mixing System

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. 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. 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. Some Current Tools
• Daniel
Courville’s
B2X
• Apple Audio
Unit and VST
plugins

45. Some Current Tools
• Swiss Centre for
Computer Music
• VST plugins

46. Some Current Tools
• University of York
• VST Plugins
• Also higher-order designs

47. Future Tools?
• Manipulate sounds in
3D space in a virtual
world?

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. 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. 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. 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. 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. 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. 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. Ambisonic Recordings
www.ambsonia.com

56. More Resources
at ambisonic.net

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?