Sascha Spors

An Analytical Approach to Sound Field Reproduction Using Circular and Spherical Loudspeaker Distributions

In this paper, we present the theoretical basics and implementation strategies for sound field reproduction using circular and spherical loudspeaker arrays. The presented approach can be seen as an analytical formulation of what is known as higher order Ambisonics. It relies on the assumption of a continuous distribution of secondary sources on which sampling is performed to yield the loudspeaker driving signals for real-world implementations. We present the theoretical derivation of the loudspeaker driving signals and investigate the properties of the actual reproduced wave field, whereby the focus lies on the consequences of the spatial discretization of the secondary source distribution.

Sound Field Reproduction Using Planar and Linear Arrays of Loudspeakers

In this paper, we consider physical reproduction of sound fields via planar and linear distributions of secondary sources (i.e., loudspeakers). The presented approach employs a formulation of the reproduction equation in spatial frequency domain which is explicitly solved for the secondary source driving signals. Wave field synthesis (WFS), the alternative formulation, can be shown to be equivalent under equal assumptions. Unlike the WFS formulation, the presented approach does not employ a far-field approximation when linear secondary source distributions are considered but provides exact results. We focus on the investigation of the spatial truncation and discretization of the secondary source distribution occurring in real-world implementations and present a rigorous analysis of evanescent and propagating components in the reproduced sound field.

Joint audio-video object localization and tracking

There has been a tremendous amount of research on object localization either involving microphone arrays or video cameras. Considerable less attention has been paid, however, to object localization and tracking based on joint audio-video processing thus far. This may be related to the lack of suitable algorithms for object localization simultaneously using multimicrophone outputs and color image sequences. In this article, we propose a solution to this problem. Before elaborating on joint audio-video processing, we review some previous work the areas of audio and video object localization. Then a recursive sensor fusion method based on decentralized Kalman filtering is introduced. Unfortunately, the decentralized Kalman filter cannot be directly used for joint audio-video object localization due to specific properties of the audio sensor. By properly adjusting the local audio position estimator, however, we manage to keep the overall architecture. We stress the general methodology.

Active listening room compensation for massive multichannel sound reproduction systems using wave-domain adaptive filtering

The acoustic theory for multichannel sound reproduction systems usually assumes free-field conditions for the listening environment. However, their performance in real-world listening environments may be impaired by reflections at the walls. This impairment can be reduced by suitable compensation measures. For systems with many channels, active compensation is an option, since the compensating waves can be created by the reproduction loudspeakers. Due to the time-varying nature of room acoustics, the compensation signals have to be determined by an adaptive system. The problems associated with the successful operation of multichannel adaptive systems are addressed in this contribution. First, a method for decoupling the adaptation problem is introduced. It is based on a generalized singular value decomposition and is called eigenspace adaptive filtering. Unfortunately, it cannot be implemented in its pure form, since the continuous adaptation of the generalized singular value decomposition matrices to the variable room acoustics is numerically very demanding. However, a combination of this mathematical technique with the physical description of wave propagation yields a realizable multichannel adaptation method with good decoupling properties. It is called wave domain adaptive filtering and is discussed here in the context of wave field synthesis.

A real-time face tracker for color video

This paper presents a face localization and tracking algorithm which is based upon skin color detection and principal component analysis (PCA) based eye localization. Skin color segmentation is performed using statistical models for human skin color. The skin color segmentation task results in a mask marking the skin color regions in the actual frame, which is further used to compute the position and size of the dominant facial region utilizing a robust statistics-based localization method. To improve the results of skin color segmentation, a foreground/background segmentation and an adaptive background update scheme are added. Additionally, the derived face position is tracked with a Kalman filter. To overcome the problem of skin color ambiguity, an eye detection algorithm based on PCA is presented.

Spatial Sound With Loudspeakers and Its Perception: A Review of the Current State

This paper reviews the current state of loudspeaker-based spatial sound reproduction methods from technical perspective as well as perceptual perspective. A nomenclature is developed that allows for a strict separation between these two perspectives. The physical fundamentals, practical realization, and results from perceptual studies are discussed for a number of well-established and emerging reproduction techniques. Further, the paper outlines novel approaches to spatial sound evaluation in terms of perceived quality and provides a comparison of current approaches.

Analytical driving functions for higher order Ambisonics

In this paper, we present the derivation and investigation of analytical expressions for the loudspeaker driving signals for higher order Ambisonics. The approach relies on the assumption of a continuous distribution of secondary sources on which sampling is performed to yield the actual loudspeaker signals for real-world implementations. For source-free volumes enclosed by the secondary source distribution, this formulation of Ambisonics leads to what is known as simple source approach. Since the simple source approach is theoretically well documented, we will depart from it and concentrate on the special case of a circular distribution of secondary point sources and derive analytical expressions for the driving signals. We furthermore derive a closed-form expression for the actual reproduced wave field for the circular secondary source distribution.

An integrated real-time system for immersive audio applications

A real-time system for immersive audio applications is presented. Sound sources are recorded using a microphone array whose beam is steered according to the output of an acoustic source localization and tracking system. The output of the beamformer (BF) along with the source position updates are continuously transmitted to a wave field synthesis (WFS) system. By using WFS, the sound sources in the recording room are rendered in the reproduction room with the correct spatial cues.

A novel approach to active listening room compensation for wave field synthesis using wave-domain adaptive filtering

Wave field synthesis is an auralization technique which allows the entire wave field to be controlled within the entire listening area. However, reflections in the listening room interfere with the auralized wave field and may impair the spatial reproduction. Active listening room compensation aims at reducing these impairments by using the playback system. Due to the high number of playback channels used for wave field synthesis, the existing approaches to room compensation are not applicable. A novel approach to active room compensation overcomes these problems by a transformation from the space-time to the wave domain and application of wave-domain adaptive filtering.

A sparsity-based approach to 3D binaural sound synthesis using time-frequency array processing

Localization of sounds in physical space plays a very important role in multiple audio-related disciplines, such as music, telecommunications, and audiovisual productions. Binaural recording is the most commonly used method to provide an immersive sound experience by means of headphone reproduction. However, it requires a very specific recording setup using high-fidelity microphones mounted in a dummy head. In this paper, we present a novel processing framework for binaural sound recording and reproduction that avoids the use of dummy heads, which is specially suitable for immersive teleconferencing applications. The method is based on a time-frequency analysis of the spatial properties of the sound picked up by a simple tetrahedral microphone array, assuming source sparseness. The experiments carried out using simulations and a real-time prototype confirm the validity of the proposed approach.