GB657546A - Communication and signal translation systems - Google Patents

Abstract

657,546. Automatic volume control; gramophone pick-ups. MULLER, E. N. Nov. 17, 1947, No. 30285. [Class 40 (iv)] [Also in Groups XXXVIII and XL (c)] A signal translation system comprises means for automatically producing or deriving auxiliary signals denoting discrete values of signal level and applying them for selecting or adjusting in stepwise manner corresponding amplitudes of main signals at a transmitter or recorder, or at a reproducer restoring the original amplitudes, the " main " and " level " signals being concurrently impressed on or derived from a single transmission or recording medium to provide accurate relative timing. The system is described applied to a multiplex pulse communication system in which succeeding pulses of one auxiliary channel periodically indicate in turn the compression of the communication pulse trains, [see Group XL (c)], and to recording and reproducing. A pick-up (Fig. 13) comprises a flat condenser electrode SC supporting the stylus S, the spacing of which from a fixed electrode CS is stepwise varied by the depth of a disc or tape record groove, the latter being selectively and stepwise varied in depth during recording in accordance with the volume level. The condenser capacity variation alters the frequency of an associated oscillator VA which is amplified, 'detected and passed through a high-pass filter CC producing at its output a sawtooth pulse 1p1 or 1p2 (Fig. 14) on each change of gain level. The positive or negative sawtooth pulses operate a trigger valve pair MV with alternative stable states to restore the correct gain level. Alternatively the recording stylus may be restored to normal record groove depth after recording a level change pulse of type 1p1 or 1p2. Further, a series of pulses 1p3, 1p4 ... may be recorded during one change of level which during reproduction may successively operate a control trigger circuit to minimise erroneous response due to a defective groove spot. The member SC may alternatively co-operate with an auxiliary magnetic structure or a piezo - electric cartridge.