Tomlinson Holman

Surrounded by sound

The authors discuss immersive audio systems and the signal processing issues that pertain to the acquisition and subsequent rendering of 3D sound fields over loudspeakers. On the acquisition side, recent advances in statistical methods for achieving acoustical arrays in audio applications are reviewed. Classical array signal processing addresses two major aspects of spatial filtering, namely localization of a signal of interest, and adaptation of the spatial response of an array of sensors to achieve steering in a given direction. The achieved spatial focusing in the direction of interest makes array signal processing a necessary component in immersive sound acquisition systems. On the rendering side, 3D audio signal processing methods are described that allow rendering of virtual sources around the listener using only two loudspeakers. Finally, the authors discuss the commercial implications of audio DSP.

Signal Processing, Acoustics, and Psychoacoustics for High Quality Desktop Audio

Integrated media workstations are increasingly being used for creating, editing, and monitoring sound that is associated with video or computer-generated images. While the requirements for high quality reproduction in large-scale systems are well understood, these have not yet been adequately translated to the workstation environment. In this paper we discuss several factors that pertain to high quality sound reproduction at the desktop, including acoustical and psychoacoustical considerations, signal processing requirements, and the importance of dynamically adapting the reproduced sound as the listeners head moves. We present a desktop audio system that incorporates several novel design requirements and integrates vision-based listener-tracking for accurate spatial sound reproduction. We conclude with a discussion of the role the pinnae play in immersive (3D) audio reproduction and present a method of pinna classification that allows users to select a set of parameters that closely match their individual listening characteristics.

Monitoring Sound in the One-Person Environment

With the growth of personal computers as display devices for media has come the need to monitor sound accompanying images on these systems. Many of the same parameters that constitute the capabilities of large-scale systems also need to be addressed in small-scale ones in order to produce similar experiences of the program material. These include frequency range and response over the range, dynamic range, and stereo imaging capabilities. In addition, some new problems also arise, such as those brought about by being too close to the loudspeakers, and the difficult acoustical environment faced by the loudspeakers. Several methods are described that make the desktop environment useful in making professional judgments of sound usually reserved for calibrated monitoring systems in motion picture dubbing stages. Having such a system extends the utility of digital audio and video workstations. Performance data are presented here.

Head-related transfer function synthesis for immersive audio

Immersive audio systems are being envisioned for applications that include teleconferencing and telepresence; augmented and virtual reality for manufacturing and entertainment; air traffic control, pilot warning, and guidance systems; displays for the visually- or aurally-impaired; home entertainment; distance learning; and professional sound and picture editing for television and film. The principal function of such systems is to synthesize, manipulate, and render sound fields in real time. In this paper we examine the limitations that are inherent in spatial sound delivery over loudspeakers and propose a method that generates virtual sound sources based on synthetic head-related transfer functions with the same spectral characteristics as those of the real source.

Immersive audio for the desktop

Integrated media workstations are increasingly being used for creating, editing, and monitoring sound that is associated with video or computer-generated images. While the requirements for high quality reproduction in large-scale systems are well understood, these have not yet been adequately translated to the workstation environment. We discuss several factors that pertain to high quality sound reproduction at the desktop including acoustical considerations, signal processing requirements, and listener location issues. We also present a novel desktop system design with integrated listener-tracking capability that circumvents several of the problems faced by current digital audio and video workstations.

Immersive audio for desktop systems

Numerous applications are envisioned for integrated media workstations to create, edit, and accurately monitor digital video and audio. There are two major classes of limitations that impede the performance of current desktop loudspeaker‐based sound systems. The first encompasses problems that arise due to the local acoustical environment, such as early reflections from the CRT and nearby flat surfaces, as well as the design characteristics and performance of the loudspeakers. The second class involves limitations that arise from variations in human listening characteristics and listener movement relative to the loudspeakers. In this paper several findings are presented that are based on acoustical, psychoacoustical, and signal processing methods for delivering accurate sound field representations. Furthermore, a novel vision‐based method for accurate listener tracking is presented that eliminates the need for headgear or tethered magnetic devices. Current findings show that this algorithm can be implemented without imposing a significant computational overhead to the host processor. Research directions include adaptive real‐time HRTF synthesis based on the tracking information, as well as vision‐based pinna shape classification for improved performance.

The history and future of DSPs in consumer audio equipment-part I: history and current conditions

The introduction of DSPs into consumer audio/video receivers was for media format decoders such as Dolby Digital and DTS decoding. To achieve greater functionality than decoding alone, additional processors were required, as decoding processes alone commanded virtually all the available capacity of DSPs of the time. Thus additional functions were limited to relatively expensive equipment that could use more than one processor. With the growth in hardware capability has come the ability to do more things. These papers trace how the rate of hardware and software development leads to increased audio capabilities, and proposes how to employ added capacity of DSP in the future.

Signal Processing Considerations for Immersive Audio Rendering

Immersive audio systems are being envisioned for applications that include teleconferencing and telepresence; augmented and virtual reality for manufacturing and entertainment; air traffic control, pilot warning, and guidance systems; displays for the visually-impaired; distance learning; and professional sound and picture editing for television and film. In this paper we examine signal processing issues that pertain to immersive audio rendering over loudspeakers. We propose two methods that can be used to implement the necessary filters for generating virtual sound sources based on synthetic head-related transfer functions with the same spectral characteristics as those of the real source. Furthermore, several factors are presented that pertain to high quality immersive audio reproduction at the desktop including acoustical and psychoacoustical considerations and the importance of dynamically adapting to listener’s head movement.

Motion-Picture Theater Sound System Performance: New Studies of the B-Chain

As the industry moves to digital delivery of sound tracks to motion-picture theaters, attention shifts to the performance of the B-Chain of the sound system, consisting of room and loudspeaker equalization, power amplifiers, crossovers and loudspeakers, screen loss, and auditorium acoustics. After choosing appropriate performance metrics, studies of the uniformity of coverage in the listening area of both steady-state and transient sound energy were performed on five motion-picture theater sound systems in situ. Conformity to the standard SMPTE 202M-1991 (ISO 2969 internationally) was measured. A hypothesis was developed regarding high-frequency uniformity of coverage and the screen-loss function

The History and Future of DSPs in Consumer Audio Equipment-Part II: Emerging Areas and the Future

The article provides a list of emerging and existing consumer audio equipment. The use of digital signal processing (DSP) with psychoacoustic methods is further discussed.