Plug-in Suite for Mastering the Production and Playback in Surround Sound and Ambisonics Matthias Kronlachner The cross-platform audio plug-ins presented here in suite provides frequently-used equalization fea- largely simplify the creation and playback of sur- tures such as levels, delays, and convolution fil- round sound productions by providing user-friend- ters to an arbitrary number of channels within one ly access to Ambisonic techniques taken from the Digital Audio Workstation. most recent research. Hereby, sound designers and The plug-in suite has already been successfully em- composers, the essential end users, can easily em- ployed in several performances with various sphe- ploy the newest ways to create, manipulate, and rical playback facilities, in the technical support play back Ambisonic recordings in variable spatial of computer musicians, and in the production of resolutions. Additionally, the multichannel plug- Ambisonic surround recordings. Figure 1: Screenshot of ambix surround plug-ins within the DAW Reaper. Introduction Digital Audio Workstation Ambisonics Spatial audio has not only been a hot research topic but provides mixing/editing and export functionality Ambisonics can be used to create spatial au- an integral part of cinema sound for many years. The add multichannel mcfx and Ambisonic ambix plug-ins: dio productions for circular or spherical louds- new generation of cinema sound technologies include peaker arrangements. In contrast to channel- + Encoders (Panner) for mono/stereo/... + Spatial effects (Reverb, Widening,...) + Multichannel Metering loudspeakers on different elevation levels thus allow for based standards in surround sound such, as + Encoders for microphone arrays + Ambisonic Format Converters + Multichannel Equalizer the playback of full periphonic surround content. While 5.1, it offers flexibility regarding the loudspea- in private homes such extensive loudspeaker installati- (Sounfield, Eigenmike, ...) + Decoders for Loudspeakers + Multichannel Convolver ker setup around the listening area. This ma- ons are still rare a major amount of music and movies + Manipulators (Rotation, Dominance,...) + Decoders for Headphones + Multichannel Delay and Gain kes the production stage largely independent is nowadays consumed through headphones. This work of the loudspeaker arrangement. Furthermo- addresses this topic by not only providing monitoring toolkits for spatial audio were developed in graphical This plug-in suite is meant to get rid of the above- re, Ambisonic content can be recorded using of surround sound over loudspeakers but also through programming environments, such as Pure Data and mentioned difficulties. It has been developed as an its classical and new main microphone array headphones. MaxMSP, which basically have no restriction concer- open source project in C++ using the JUCE framework technology. ning the number of channels and offer quick develop- which supports building audio plug-ins in all major for- Ambisonics is based on the expansion of the For several years research institutions have been expe- ment and maintenance cycles. mats and standalone audio applications for Windows, surround signal into spherical harmonics up rimenting with loudspeaker arrays in two- and three- However, not only is the integration of such external MacOS and Linux. Currently the software is provided to the order N that defines the angular reso- dimensional setups. Many individual software solutions spatialization toolboxes into a DAW challenging for the as VST and standalone binaries for Windows and MacOS. lution. A full periphonic (3D) Ambisonic sig- were developed that support the creation of content developer, these toolboxes are often also challenging to nal set of order N results in ( N + 1) 2 channels. for these loudspeaker arrangements. While most Digi- use for non-experts. Audio channels and control data Using flexible DAWs such as Reaper or Ardour allows tal Audio Workstations (DAWs) provide tools to pro- have to be sent between the applications and complex for a single software controlling the entire production The maximum Ambisonic order N for all am- duce for standard surround setups such as 5.1 only, routing scenarios need to be re-established everytime. cycle starting from panning the source signals, mixing bix plug-ins can be defined at compile time more extensive loudspeaker setups (eg. Fig. 4) clearly This frequently causes difficulties when sharing pro- microphone array recordings until decoding the play- and is only limited by the maximum number require tools for a more flexible channel routing. jects and due to the loss of the ability to render audio back signals and adjusting the loudspeaker signals. of channels per track of the host. To overcome the limitation of DAWs, most tracks offline. mcfx_filter mcfx_convolver Head Tracking Binaural Decoder Microphone . Ambisonic left . Array . signals Ambisonic . Headphone . Rotation . Surround Signal Signals right Figure 4: Adjusting the sonic charactersitic of microphone array recordings and converting to Ambisonics. ambix_rotator ambix_binaural Figure 9: Listening to Ambisonic recordings using virtual louds- peakes and binaural loudspeaker impulse responses, headtra- cking controls the rotator for a stable surround image. Decoder matrices are obtained using the AllRAD method [4]. Figure 7: Ambisonic metering, RMS and peak me- ters distributed on the surface of a sphere. mcfx_filter mcfx_delay_gain Delay Gain Figure 2: ambix_encoder is used for panning mono or Loudspeaker . Figure 5: Example microphone arrays that have been used: . multichannel sound sources on a surface of a sphere. Signals . (a) 32 channel mh acoustics Eigenmike [1] and 4 channel Delay Gain (b) Soundfield and (c) Coresound Tetramic. individual OSC/UDP connection from visualization to encoders Figure 10: Multichannel filter and delay/gain for adjusting a azimuth, elevation Visualization loudspeaker array on the fly. Encoder OSC/UDP and azimuth, elevation, Remote Control Encoder audio level Loudspeaker array ambix_encoder mcfx_convolver ... ambix_warp allows to adjust the spatial Sound Encoder Figure 8a: . perspective of the surround mix. Source . Digital Audio Workstation Thin lines indicates unmodified surround image, azimuth, elevation upper scheme: warping towards the northpole Built in OSC layer for monitoring and control- Figure 3: lower scheme: warping away from equator [2]. ling multiple encoders from one central point, this appli- Figure 11: Ambisonics signals can also be used to control the Figure 8b: ambix_widening performs a frequency cation may run on the same computer or on a different radiation of loudspeaker arrays. This scheme shows the usage Figure 6: ambix_converter allows to convert between dif- dependent z-rotation and can be used to widen the device connected via network. for the IEM icosahedral loudspeaker array [5]. ferent Ambisonic formats. source or synthesize early reflections [3]. Figure 12: Examples for surround concert venues where the software was already used. ambix_binaural comes with binaural loudspeaker impulse responses of the Cube and Mumuth which allows to virtually listen to your surround production within those venues using headphones and headt- racking. The software was used for performances using 4-43 loudpseakers so far. 1 12 23 18 2 10 20 13 Sub 17 11 11 3 9 2 19 24 21 14 8 +90° 3 10 4 22 16 R1 12 19 23 22 18 7 4 +59° 15 9 6 +50° 5 17 +28° 16 5 13 15 0° 8 14 0° 6 21 20 7 Ring on floor (-45°) (a) Loudspeaker layout and (b) panoramic picture of the IEM CUBE with 24 loudspeakers. (b) Mumuth, Graz, 29 loudspeaker hemisphere. (c) Observatory of Vilnius University, (d) 23 loudspeaker layout. Conclusion The software has already been successfully used References A suite of cross-platform Ambisonic and multi- by professionals and students for the production [1] S. Lösler, “Schallfeldspezische Entzerrung bei Radialfiltern begrenzter Dynamik für das Eigen- channel effect plug-ins has been presented. The of 3D surround sound and formed an integral mike“, Project thesis, Graz, 2013. software allows to use extensive multichannel part of the concert setup in various venues. [2] M. Kronlachner and F. Zotter, “Spatial transformations for the enhancement of Ambisonic recor- microphone and loudspeaker arrays within Di- dings“, in 2nd International Conference on Spatial Audio, Erlangen, 2014. gital Audio Workstations. By keeping the who- Acknowledgment [3] F. Zotter, M. Frank, M. Kronlachner, J.-W. Choi, “Efficient Phantom Source Widening and Dif- le production within one host, the editing and fuseness in Ambisonics“, EAA Symposium on Auralization and Ambisonics, Berlin, 2014. The author would like to thank the Music Inno- offline rendering functionality of DAWs can be [4] F. Zotter, M. Frank, “All-Round Ambisonic Panning and Decoding“, Journal of the Audio Engi- vation Studies Centre Vilnius where parts of the used to efficiently create and share immersive neering Society, October, 2012. development and tests where carried out. surround productions. [5] F. Zotter, “Analysis and Synthesis of Sound-Radiation with Spherical Arrays“, IEM, University of Music and Performing Arts Graz, 2009. AES Students Design Competition Software available here: Institute of Electronic Music and Acoustics INSTITUTBerlin, Germany, 1 April 26-29, 2014. Komposition, Musiktheorie, -geschichte und Dirigieren www.matthiaskronlachner.com Inffeldgasse 10 / III, 8010 Graz, http://iem.at Matthias Kronlachner.