Mosca

Extension

Description

Mosca is a SuperCollider class for GUI-assisted production of sound fields with simulated moving or stationary sound sources. Input sources may be any combination of mono, stereo or B-format material and the signals may originate from file, from external inputs (physical or from other applications via Jack) or from SuperCollider's own synths. In the case of synth input, each is associated by the user with a particular source and registered in a synth registry. This way, they are spatialised and also receive data from the source control (eg. x, y and z coordinates or auxiliary fader data). Ambisonic Sound fields may be decoded using a variety of built-in decoders (including binaural), Faust Ugens created with the AmbiDecodertoolbox (see HOA decoding) or with external decoders such as Ambdec. Mosca has its own transport provided by the Automation quark for recording and playback of source data. This can be used independently or may be synchronised to a DAW using Midi Machine Control (MMC) messages. This function has been tested to work with Ardour and Jack. The integration of ossia-sclang also allows Mosca's individual parameters to be controled with the interactive sequencer Ossia/score as well as any other application featuring OSCQuerry or plain OSC communication.

Sources

Mono and stereo sources may be spatialized with ugens from a selection of libraries (Ambitools, HoaLib, ADT, ATK, BF-FMH, Josh & VBAP) set indiviualy for each source. For B-format input signals, which are already ambisonically encoded, the available options for transformation the ATK and Abitools. The ATK is used to implement push transformations to manipulate the angular location of sources as well as to perform rotations of the source sound field and to manipulate its directivity. Ambitools is used to implement a beam formation technique. All sources are subject to high frequency attenuation with distance. For a better sensation of nearness, ATK implements a proximity effect, adding a bass boost to proximal sources among other phase effects to simulate wave curvature. To that same effect, the Ambitools encoder makes use of "Near Field Compensation". Generally, the differences between libraries can be summarised as follows:

Reverberation

Reverberation is performed either using a B-format tail impulse responses (IRs) or by using reverberators crated with SuperCollider's AllpassC and FreeVerb ugens. With both options, two reverberation level controls are included in the GUI for setting close and distant levels. "Close" reverberation in this case is "global" and is audible by the listener from all directions when the source is close. As it is global, it's type is applied to the entire scene. "Distant" reverb on the other hand is "local" in scope and selected and applied on a per-source basis. It is processed by the individually selected spatialiser along with the dry signal. This effect predominates as the source becomes more distant. For ambisonic signals, the "Close" reverberation may be described as a "2nd order diffuse A-format reverberation". This technique produces reverberation weighted in the direction of sound events and involves conversion to and from A-format in order to apply the effect (ANDERSON). The encoded 2nd order ambisonic signal is converted to a 12-channel A-format signal and then either:

• convolved with a B-format IR which has been "upsampled" to 2nd order and converted to A-format impulse spectrum
• passed through Freeverb or allpass ugens before being converted back to a 2nd order B-format diffuse signal

For non-ambisonic signals, spatialised with VBAP, a part of the original source signal is mixed with the W component of the B-format reverb input for an omnidirectional effect. These options are drawing from John Chowning's technique of applying "local" and "global" reverberation to sources (CHOWNING)

Additional Features

Additional features include a scalable Doppler Effect on moving sources, the looping of sources loaded or streamed from file and the adjustment of the virtual loudspeaker angle for stereo sources. Further, a "contraction" control enables crossfades between B-format signals and their raw W component. In the case B-format input signals the contraction changes the sound from having omnidirectional characteristics to becoming a focussed point source. When using the ATK in the case as mono or stereo input sources (the latter of which are treated as two mono sources with adjustable angle from one another) with the ATK, a de-contraction of the focussed source will render it omnidirectional.

Mosca supports methods for making "A-format inserts" on any source spatialised in the GUI. In this way, the user may write a filtering synth and apply it to the sound without disrupting the encoded spatial characteristics. Please see the guide for examples.

Additionally, Mosca v0.2 implements headtracking with the Arduino 9-axes Motion Shield and an appropriate Arduino board such as an Uno. Mosca may also run GUI-free and has a mechanism for coded control of the interface (Setup example in the guide).

Acknowledgments

The class makes extensive use of the Ambisonic Toolkit (ATK) by Joseph Anderson as well as Florian Grond's SC-HOA, based on Ambitools by Pierre Lecompte, the faust version of the HoaLibrary by Pierre Guillot, the AmbiDecoderToolbox and sevral other supercollider pluggins for spatial renderding. Augmented controll has been granted by the integrating the Automation quark by Neels Hofmeyr and ossia-sclang, made possible by Pierre Cochard, Jean-Michaël Celerier and the OSSIA Team.

Many thanks to Joseph Anderson, Neels Hofmeyr and members of the SuperCollider list for their assistance and valuable suggestions.

References

ANDERSON, Joseph. Authoring complex Ambisonic soundfields: An artist's tips & tricks. DIGITAL HYBRIDITY AND SOUNDS IN SPACE JOINT SYMPOSIUM. University of Derby, UK: 2011.

CHOWNING, John M. The Simulation of Moving Sound Sources. Computer Music Journal, v. 1, n. 3, p. 48-52, 1977.

GROND, Florian & LECOMPTE, Pierre. Higher Order Ambisonics for SuperCollider. Linux Audio Conference, Jean MONNET University. Saint-Etienne France: 2017.

CELERIER, Jean-Michaël. Authoring interactive media : a logical & temporal approach. Ph. D dissertations, University of BOrdeaux, France: 2018.

Class Methods

.new

.printSynthParams

Instance Methods

.gui

.headTracker

.getSCBus

.playAutomation

.loadAutomation

Examples

The following is a basic Binaural Setup, see guide-Mosca for more examples( Server.killAll; // Make sure no servers are running yet // Create and name an OSSIA_Device to contain all of Mosca's parameters ~supercoll = OSSIA_Device('SC'); ~supercoll.exposeOSC; // Enable OSC communication with the OSSIA_Device o = s.options; o.numInputBusChannels = 32; // Allow for many possible inputs o.numOutputBusChannels = 2; // Stereo output for binaural rendering o.numAudioBusChannels = 2048; o.numWireBufs = 512; s.waitForBoot { // Booting scsynth server before setting up Mosca // Set global variable passed as Mosca's arguments ~decoder = FoaDecoderKernel.newCIPIC(21, s, s.sampleRate.asInteger); // ATK Binaural MIDIIn.connect(); // must connect to MIDI for MMC synchronisation s.sync; ~moscaInstance = Mosca( //autoDir: "/path/to/project/folder", //irBank: "/path/to/irBank/folder", nsources: 11, // Set the number of sources decoder: ~decoder, parentOssiaNode:~supercoll; ).gui(); }; )