ENGINEERING REPORTS Phantom SourcesApplied to Stereo-BaseWidening*

A stereo-base widening system producing a good effect, achievable with a simple analog circuit as well as with a digital one, is presented. The system is derived from a combination of the traditional approachusing head-relatedtxansfer functions (HRTFs), and by using a simple model where ideal loudspeakers and an acoustically transparent subject's head are assumed. Both the HRTF approach and the simple model are discussed, and some special eases for the latter are considered. Merging these models with some experimentally deter-minedadaptationsled to a practicalwidening system. The system producesa pleasant and naturalsound, particularlyfor voices and normalmixed stereo recordings.The widening circuit is tuned in such a way that for common stereo recordingsit gives the same tonal balance as conventional stereo reproduction. For sound effects as in action movies, the system producesextremeeffects, which was a deliberatedesign goal of the system. 0 INTRODUCTION known as TRADIS (true reproduction of all directional information by stereophony). A vast amount of literature It is hardly possible to image sound reproduction to- followed, in the form of papers (see, for example, [25], day without stereophonic techniques, and it is to the [26]), but mostly through patents. According to a paten