GB288225A - Method of and means for eliminating disturbing noises in the optical reproduction of sound records - Google Patents

Abstract

288,225. Siemens & Halske Akt.-Ges. April 9, 1927, [Convention date]. Optical apparatus and records.-To eliminate ground noises in the reproduction of photographic ,sound records, the non-recorded part of the record is shuttered, either in the recording or the copying process, up to the envelope of the sound trace, particularly at the parts of the trace of small amplitude. This may be effected, according to one method, by covering the transparent portion of a positive made from a negative with a non- transparent colour up to the envelope of the trace. Alternatively the negative record may have the blackened part removed, by known reducers, up to the curve enveloping the record so that on making a positive therefrom only the part within the envelopo remains unblackened. Another method consists in apply a mark s, Fig. 7, corresponding to the envelope to a positive film made from a negative and again exposing to light. The resulting record according to the invention is shown in Fig. 2 wherein the envelops embracing the sound trace is the only part through which light can pass in reproducing. In another method, which avoids the necessity for additional blackening of the record, provision is made for automatically actuating a shutter from the record during reproduction so that light passes only through a width corresponding to the envelope of the sound trace. In this arrangement a beam from a source l, Fig. 9, directed through the record on to a cell z is variably intercepted by a shutter m, n, Fig. 10. comprising a fixed plate m and a plate n provided with an inclined edge and movable towards and away from the plate m by a pivoted lever q actuated by an electromagnet r in the circuit of a selenium cell p influenced by a beam directed through the record. This beam is spaced along the record o at such a distance from the reproducing beam that the lag in the circuit of the electromagnet r is compensated. The arrangement of Fig. 9, can be used in recording by substituting an auxiliary microphone for the cell p in the electromagnet circuit.