~Proceedings ICMCISMCI2014 14-20 September 2014, Athens, Greece
Supporting tracks of up to 64 channels, 4 it is exceptionally
open-ended with respect to routing of both channels and
tracks. All standard fixed-channel surround sound configurations are supported, and the included ReaSurround panning plugin caters for non-standard speaker configurations
[10]. Flexible routing makes Reaper well-suited for Ambisonics; it is a preferred DAW for many composers within
the Ambisonic community. 5 Additionally, Reaper's FX
Chains feature conveniently allows plugin chains to be
saved as presets.
1.3 Plugins for Ambisonic processing
In recent years a number of plugins have emerged for Ambisonic processing. WigWare is a set of VST plugins for
Mac and Windows that includes FOA and HOA panners
and decoders for regular and irregular speaker layouts, as
well as an FOA 3D reverb.6 Courville has developed a
suite of FOA, 2nd order and TOA plugins 7. These include
encoding and decoding, rotations, reverb, and additional
convenient utilities. Additionally encoders and decoders
for 5th order pantophonic 8 are also available. Unfortunately, the plugins are developed using SonicBirth9, and
due to the long halt in development of this framework,
these plugins do not work reliably in all newer DAW versions. ambiX are cross-platform FOA, TOA and 5th order Ambisonic processors for encoding and decoding, including binaural decoding, as well as spatial transforms
[11, 12]. These plugins use the ambiX encoded signal convention, ACN channel ordering with SN3D normalization
[13], but also provides a conversions utility for other formats. They are accompanied by mcfx, a number of more
general multichannel plugins for equalising, delay, gain
adjustment and level metering [14]. Flux Ircam Spat wraps
the Ircam Spatialisateur multiformat room acoustics simulation and localization software as AU and VST plugins
for Mac and Windows [15]. Although this plugin mainly
provides object-based scene descriptions, it can render the
auralization as B-format. The HARPEX plugin for decoding FOA uses a spatial upsampling algorithm based on
high angular resolution planewave expansion (HARPEX)
in order to expand the smaller sweet spot of FOA to HOA
extents [16]. Blue Ripple Sound offers a wide range of
OSX and Windows VST plugins for TOA, 10 including encoders, transcoders and decoders, and a rich set of plugins
for spatial filtering of the encoded signal. Moreover, TOA
includes a HARPEX upsampler, facilitating FOA to TOA
conversion via the HARPEX algorithm.
2. AMBISONIC TOOLKIT
The Ambisonic Toolkit (ATK) brings together a number
of tools and transforms for working with Ambisonic surround sound [17]. Use is targeted towards the composer of
4 Suitable for 7th order HOA.
5 http://www.brucewiggins.co.uk/?pageid=215
6 http://www.brucewiggins.co.uk/?page-id=78
7 http://www.radio.uqam.ca/ambisonic/b2x.html
8 Horizontal only.
9 http://sonicbirth.com/
10 http://www.blueripplesound.com/product-listings/pro-audio
acousmatic and experimental music. The intention is for
the toolset to be both ergonomic and comprehensive, providing algorithms to creatively manipulate and synthesize
Ambisonic soundfields.
By focusing on the problem of synthesising and processing soundfields, the tools are framed for the user to 'think
Ambisonically'. The model of the ATK is a sound-field
sound-image model rather than a sound-object sound-scene
model. In addressing the holistic problem of creatively
controlling a complete soundfield, the ATK allows and encourages the composer to think beyond the placement of
sounds in a sound-space and instead attend to the impression and image of a soundfield. This is viewed to be the idiomatic approach for working with Ambisonic technique,
leveraging the model the technology presents.
The ATK has existed in a variety of forms since 1998,
beginning as a collection of Csound orchestras, and later
as a set of privately distributed VST plugins. Development of the real-time ATK library for SuperCollider2 began in 2000, and in recent years ATK has primarily been
distributed as a version for SuperCollider3 [17]. Some of
the underlying ideas of ATK has also been incorporated
into the Blue Ripple Sound TOA plugins.
2.1 Ambisonic Toolkit Paradigm
Figure 1 illustrates how the ATK separates the task of production work with Ambisonics into three distinct elements:
Author: Capture or synthesise an Ambisonic soundfield.
Image: Spatially filter an Ambisonic soundfield.
Monitor: Playback or render an Ambisonic soundfield.
In its most simple form, Ambisonics can be regarded as
splitting the panning law into two separate parts: encoding
(Authoring) and decoding (Monitoring), where final panning (decoding) is deferred to an actual loudspeaker array
at the time of audition. The ATK considers Imaging (transforming) a soundfield to be an critical step; this is where
the artist shapes and processes the soundfield in a coherent
way which isn't easily available via the other models for
working with spatial sound. Further details are discussed
in section 4, below.
Many publicly distributed implementations of Ambisonics provide only encoding and decoding. While giving
flexibility regarding final playback, failing to include transformers misses out the concept of imaging and fails to capitalise on the advantages of the sound-field sound-image
paradigm intrinsic to Ambisonics.
3. ATK REAPER: DESIGN CONSIDERATIONS
3.1 Choice of plugin architecture
When porting ATK for use in a DAW environment the
prime question is whether to implement plugins in C++
using plugin architectures such as VST 11 or AudioUnit
11 http://www.steinberg.net/en/company/developer.html
- 1339 -
