Meeting Topic: Ambisonics and the Ambisonic Toolkit
Speaker Name: Joseph Anderson, University of Washington DXARTS
Other business or activities at the meeting: Noted the International AES AVAR (Audio for Virtual and Augmented Reality) Conference to be held at DigiPen on Aug. 20-22, 2018.
Meeting Location: University of Washington DXARTS, Raitt Hall, Seattle WA
The PNW Section met on Wednesday, November 15, 2017 at Raitt Hall on UW's campus for a presentation by Joseph Anderson called "Ambisonics and the Ambisonic Toolkit (ATK)," hosted by University of Washington's DXARTS (Center for Digital Arts & Experimental Media). There were 60 attendees, including 24 AES members.
Section chair Dan Mortensen gave a short introduction to the meeting and welcomed everyone. Matt Klassen, professor of mathematics at DigiPen Institute of Technology, and Bob Moses, executive director of the AES, both provided an announcement for the upcoming International AES AVAR (Audio for Virtual and Augmented Reality) Conference to be held at DigiPen on Aug. 20-22, 2018.
Joseph Anderson began by discussing some required readings for anyone interested in learning more about the theory and mathematics behind ambisonic sound techniques. Anderson describes ambisonics using the following terms: holographic, heriphonic, rational, convenient, isotropic, "scene based," and hierarchical. Anderson explained terms relating to ambisonics such as sound fields, first-order ambisonics (FOA), higher-order ambisonics (HOA), ambisonic encoding and decoding, A-format vs. B-format ambisonic signals, and A-format tetrahedral microphone arrays. Various formats of first-order and higher-order ambisonics and their properties were discussed. Anderson went over some of the current software technologies available for production and research for audio engineers and composers wishing to explore ambisonic encoding, processing (transformation), and decoding.
Anderson then introduced the design of DXARTS multiple ambisonic studios which each feature large multi-channel speaker arrays. Depending on the studio the speaker arrays are arranged in either mid-field or near-field positioning and either in a spherical or hemi-spherical distribution. Anderson discussed some of the challenges in calibrating these speaker systems using a digital room correction process that corrects for the distance, tonal response, phase response, and proximity of the loudspeakers. This correction is done with a custom program developed at DXARTS featuring a set of FIR filters.
Anderson then began to discuss his work on developing the Ambisonic ToolKit (ATK). The ATK allows users to encode, transform, and decode ambisonic signals using software such as SuperCollider or Reaper. Joseph thanked the various composers, engineers, and programmers who had helped him along the way developing this software. Developers include Juan Pampin (Director of DXARTS), Joshua Parmenter, Michael McCrea, Trond Lossius, and Daniel Petersen along with institutional support from Bergen Center for Electronic Arts and Oslo National Academy of the Arts. The SuperCollider version of ATK is the most mature and the Reaper version is a subset.
Various types of transformation of the ambisonic signal, or soundfield kernel, were discussed and how they can be used creatively. In addition, Anderson explained different creative approaches to making recordings and mixing music using ambisonic techniques.
At this point in the meeting we took a brief break for cookies and water and conversation. During the break door prizes were awarded:
• AES coasters won by Rob Miller and Rick Chinn
• Belden CAT cable tool (courtesy Steve Lampen/Belden) won by Tom Stiles
Joseph Anderson, our presenter, provided several Ambisonic CDs for door prizes:
• Joseph Anderson Ambisonic CD, "Epihanie Sequence" won by Drew Cady
• Jos Zwaanburg Ambisonic CD, "20 ODD YEARS: Music for Flute and Electronics" won by Keith Sjoquist
• Juan Pampin Ambisonic CD, "Percussion Cycle: Les Percussions de Strasbourg" won by Miles Gardner
• Jonty Harrison Ambisonic CD, "Voyages," won by Jayney Wallick
Immediately following the break, attendees were treated to a series of three different demos using ATK that took place in three different DXARTS' ambisonic sound projections spaces. These demos included a work for horn and electronics by composer Ewa Trebacz, performed by Josiah Boothby. Trebacz's work focused upon utilizing ambisonic room impulse responses (RIR) taken from the Fort Worden cistern. Another demo by Daniel Petersen and Martin Jarmick explored virtual reality and holographic sound synthesis using the ATK. Finally, James Wenlock presented his ambisonic tank reverb model for SuperCollider 3 called, AmbiVerbSC.
After the demos, attendees were very curious to ask Anderson many questions regarding ambisonics. Questions from attendees ranged from understanding the concept of a panning laws, how to choose the right loudspeakers for ambisonics, recommendations for ambisonic microphones, and recommendations for ambisonic plug-ins.
Written By: Greg Dixon, PNW Section Committee