Abstract: Apparatus for recording and reproducing audio signals on flat rectangular recording media comprising a magnetic coating or the like on at least one side. A magnetic head on a swing arm moves across the magnetic media in mutually parallel lines guided by a heart-shaped cam, the recording medium being stationary during recording and reproducing so its visible surface can be examined without difficulty. The heart-shaped cam is of asymmetric configuration, and the magnetic head is pivotably mounted on one end of the swing arm which carries between its ends a cam follower peg which continually engages the heart-shaped cam while under spring loading. The other end of said swing arm is pivotably mounted on a sliding carriage plate which is moved stepwise perpendicularly to the chord of the curved path of movement of the magnetic head for each line. The stepwise perpendicular movement of the sliding carriage plate is produced by a mechanism which is controlled by the reversal of direction of the magnetic head.

Abstract: The arm carrying the optical head that projects and focuses a light beam onto a record trace on a video disc record is provided with a tracking movement by mounting the arm on an electromagnetically driven moving coil system that produces torque, driving the arm radially of the disc in accordance with a combination of coarse and fine tracking correction signals. The light beam is deflected by mirrors both at the pivot of the arm and at its extremity. The mirror at the arm extremity is either associated with a focusing lens or else provided with a parabolic curvature so that the light beam will be narrowed to a spot on the record trace. For transparent records, a photocell on the other side of the record disc is carried on a second arm mounted on the same torque-producing moving coil system in a manner elastically rather than rigidly coupled to the moving coil structure. In a system for opaque discs, the arm extremity deflecting mirror is a half mirror and the photocell is mounted behind the half mirror.

Abstract: The principle of the Foucault knife edge method of testing lenses is utilized by providing an imperfect focus of the reading light beam on the signal track of a moving optical record and detecting the lateral distribution of light beyond the track to produce a tracking control while a centered detector utilizes the same light beam to read the information on the track. Since the Foucault principle is used and not ordinary shadow effect, the method is operable just as much with a translucent track on an opaque record as with an opaque track on a translucent record.