Spatial Sound Recording and Transmission Systems: Status, Problems, and Prospects

Contemporary analog and digital signal processing techniques have 'been refined to the point of being able to routinely convey individual audio channels with little or no perceptible loss of quality. The greatest disparity between original anti reproduced soundfields usually involves their spatial characteristics. Improving the spatial fidelity of audio recording and transmission systems involves understanding the underlying localization mechanisms, then applying this understanding to evolve specific system requirements, subject to the constraints of real world components and practices. Spatial audio systems are conveniently dividable into three functional blocks: 1. soundfield pickup, via one or more microphones and/or electronically synthesized signals, 2. means for coding, transmission (or recording/playback), and decoding of the net source audio signals, and 3. soundfield reconstruction, via loudspeakers or headphones, and possible associated processing. The presentation environment exerts sufficient influence on system configuration to have spawned several classes of spatial audio systems, e.g. home, headphone, and theatre systems. Conventional home stereo is currently the most common spatial audio system in use. It purports to encode a horizontal continuum of space into a pair of audio channels, which are then conveyed via a discrete two channel medium to a pair of loudspeakers. This system relies on the psychoacoustic phenomenon of phantom images; to try to fill the space between the speakers. Related techniques, such as 'Sonic Holography' or Q-Sound, attempt to extend the range of horizontal space conveyed, in part by using interaural cross cancellation to extend the apparent reproduced image beyond the arc of the speakers. Microphone pickup arrangements for stereo recording vary widely, and are often a matter of strong individual preference on the part of recording producers. It is desirable for newly developed systems to retain this option.