Scanning system for reproducing side-by-side optical sound tracks

Claim 1

A scanning system for reproducing a plurality of side-by-side variable area optical sound tracks, comprising scanning means arranged to scan repeatedly across the width of all of said tracks in each scan to provide a two-level first electrical signal; a plurality of bistable circuits; gating means coupled between said scanning means and said bistable circuits; a source of gating signals synchronized to said scanning means and operating said gating means to pass portions of said first signal corresponding to the different sound tracks to different ones of said bistable circuits; each said bistable circuit providing a two-level second signal and being responsive to the first signal portion gated thereto to set its second signal from a first level to a second level in response to a transition in the first signal occurring as said scanning means scan from an opaque area to a clear area of the corresponding sound track; delay means operative to delay setting of each bistable circuit until said transition in the first signal is followed by maintenance of the first signal at a level corresponding to a clear area of the corresponding sound track for a predetermined length of time established by the delay means; and means for resetting said bistable circuits at reference instants, independently of said first signal, thereby to reset said second signals from said second level to said first level.