Abstract: Audio information is recovered from a variable-area optical record, particularly motion picture film variable-area optical soundtracks. A scan signal is obtained by repetitively scanning the optical record substantially transverse to the bias line. The noise reduction effect is enhanced by a threshold detector which is provided with a transversely varying threshold level that varies according to the position of the scan across the width of the soundtrack. A threshold is provided for a bilateral soundtrack, the threshold having a minimum level at the bias line of the soundtrack and increasing progressively with distance from the bias line. Thus, one each scan, the threshold level is high when the scan is at the edge of each soundtrack, falls progressively to a minimum when the scan reaches the bias line, and then increases progressively back to its original high level when the scan is at the other edge of the soundtrack.

Abstract: An electric piano has a complete player actuated piano voice of which harmonics are basically controlled by a tuning fork that is struck by the piano key. The piano is also provided with an electronically generated voice of which harmonics are electronically generated. To better enable the two voices to be played simultaneously by striking a single piano key, the amplitude envelope of the electromechanically generated piano voice is imposed upon the electronically generated voice which is gated and amplitude modulated so as to be heard in precise synchronization with a piano note produced by the instrument player. Linearity of modulation is extended to low piano voice amplitudes by use of modulating and gating diodes in oppositely poled feedback paths of an operational amplifier.