Matthias Geier

Spatial perception of sound fields recorded by spherical microphone arrays with varying spatial resolution

The area of sound field synthesis has significantly advanced in the past decade, facilitated by the development of high-quality sound-field capturing and re-synthesis systems. Spherical microphone arrays are among the most recently developed systems for sound field capturing, enabling processing and analysis of three-dimensional sound fields in the spherical harmonics domain. In spite of these developments, a clear relation between sound fields recorded by spherical microphone arrays and their perception with a re-synthesis system has not yet been established, although some relation to scalar measures of spatial perception was recently presented. This paper presents an experimental study of spatial sound perception with the use of a spherical microphone array for sound recording and headphone-based binaural sound synthesis. Sound field analysis and processing is performed in the spherical harmonics domain with the use of head-related transfer functions and simulated enclosed sound fields. The effect of several factors, such as spherical harmonics order, frequency bandwidth, and spatial sampling, are investigated by applying the repertory grid technique to the results of the experiment, forming a clearer relation between sound-field capture with a spherical microphone array and its perception using binaural synthesis regarding space, frequency, and additional artifacts. The experimental study clearly shows that a source will be perceived more spatially sharp and more externalized when represented by a binaural stimuli reconstructed with a higher spherical harmonics order. This effect is apparent from low spherical harmonics orders. Spatial aliasing, as a result of sound field capturing with a finite number of microphones, introduces unpleasant artifacts which increased with the degree of aliasing error.

Object-based audio reproduction and the audio scene description format

The introduction of new techniques for audio reproduction such as HRTF-based technology, wave field synthesis and higher-order Ambisonics is accompanied by a paradigm shift from channel-based to object-based transmission and storage of spatial audio. Not only is the separate coding of source signal and source location more efficient considering the number of channels used for reproduction by large loudspeaker arrays, it also opens up new options for a user-controlled interactive sound field design. This article describes the need for a common exchange format for object-based audio scenes, reviews some existing formats with potential to meet some of the requirements and finally introduces a new format called Audio Scene Description Format (ASDF) and presents the SoundScape Renderer, an audio reproduction software which implements a draft version of the ASDF.

The multi-touch SoundScape renderer

In this paper, we introduce a direct manipulation tabletop multi-touch user interface for spatial audio scenes. Although spatial audio rendering exists for several decades now, mass market applications have not been developed and the user interfaces still address a small group of expert users. We implemented an easy-to-use direct manipulation interface for multiple users, taking full advantage of the object-based audio rendering mode. Two versions of the user interface have been developed to explore variations in information architecture and will be evaluated in user tests.

The future of audio reproduction: technology - formats - applications

The introduction of new techniques for audio reproduction such as binaural technology, Wave Field Synthesis and Higher Order Ambisonics is accompanied by a paradigm shift from channel-based to object-based transmission and storage of spatial audio. The separate coding of source signal and source location is not only more efficient considering the number of channels used for reproduction by large loudspeaker arrays, it will also open up new options for a user-controlled soundfield design. The paper describes the technological change from stereophonic to array-based audio reproduction techniques and introduces a new proposal for the coding of spatial properties related to auditory objects.

The interactive soundscape renderer for loudspeaker- and headphone-based spatial sound presentation

We demonstrate the SoundScape Renderer (SSR), which is an open-source software package that performs realtime spatial sound reproduction based on various different loudspeaker-based methods as well as headphones. The implemented algorithms include wave field synthesis, amplitude panning Ambisonics, VBAP, and binaural reproduction amongst others and cover the entire range from single-person sound reproduction to large-scale loudspeaker arrays. SSR comprises a TCP/IP interface that allows for its entire functionality to be controlled remotely. Any software running on any platform can connect to SSR and serve as a remote control. We describe two such examples: 1) The BoomRoom, a system for mid-air direct interaction with virtual sound sources, and 2) an Android-based remote control that allows for interaction with SSR using the touch screen of a smartphone.