Practical Systems for Quasi-Stereophony

Abstract

Artificial- or quasi-stereophony derives different multiple signals from a monophonic signal by means of (linear) filtering. The derived signals are then radiated from two or more separated loudspeakers. For certain filtering conditions and loudspeaker placements, a diffuse sound image is created which has the same “ambience” (spatial spread) as true stereophonic reproduction. Quasi-stereophony cannot, of course, duplicate the localization of true stereophony. However, it has been found that ambience, by avoiding the unrealistic impression that all sounds come from a small area, is as important to stereophonic-sound projection as the ability to localize correctly individual sound sources. Several practical systems for quasi-stereophonic reproduction are described. A new approach to artificial stereophony [J. Acoust. Soc. Am. 33, 1061 (1961)] using all-pass filters to avoid spectral distortions is demonstrated.