GB622698A - A monitoring circuit arrangement - Google Patents

Abstract

622,698. Monitoring circuits. BOSTON, D. W. Jan. 16, 1947, No. 1484. [Class 40 (iv)] In a sound-recording apparatus, particularly for sound films, a monitoring circuit is provided which indicates when over-recording is taking place by limiting the peaks of the sound waves in the same way as in the recording system. In a variable-width system in which the maximum width of the track is limited by the finite dimensions of the part of the film allotted for the sound track, the peaks of the sound waves are cut off during over-recording in the manner indicated in Fig. 1 and distortion occurs. The monitoring circuit is branched off from the main recording channel and may take the form of two diodes D1, D2 connected as shown in Fig. 2, in which the signal passes from the input terminals I to the output terminals O without distortion until the signal voltage exceeds that of the batteries B1, B2. When this occurs the diodes D1, D2 become conductive and the peaks of the waves are cut in a manner similar to that shown in Fig. 1, and audible distortion is produced in a monitoring loudspeaker. The control R may be set to a position in which the distortion in the monitoring circuit occurs simultaneously with, or slightly before, distortion occurring in the recording system. The monitoring circuit may be provided with an output transformer T1 and cathode-ray tube C1 as shown in Fig. 4, so that no indication appears until distortion commences. An alternative peak limiting and indicating circuit, Fig. 5 (not shown), takes the form of a triode valve followed by a glowdischarge lamp which strikes when distortion is taking place in the recording system, and serves both to limit the peaks in the monitoring circuit and act as an indicator at the same time.