GB523787A - Improvements in and relating to electric wave systems - Google Patents

Abstract

523,787. Automatic volume control. TELEPHONE MANUFACTURING CO., Ltd., and PADDLE, L. H. Jan. 13, 1939, No. 1210. [Class 40 (iv)] In a volume range compressor or expander, using a network of non-linear impedances in the transmission path the attenuation of which is controlled over a path connected to the input or output compressor or expander respectively, a further network of non-linear impedances is included in the control path, both networks being controlled in accordance with the amplitude of the signals in' the control path. The invention is applicable to telephone systems, with or without radio links, radio broadcast systems and gramophone recording and reproducing systems. In the compressor shown in Fig. 1a, the output of rectifier M5 in the control path, fed over pad AP2 from the input 10, is applied over circuits including separate bias batteries B1, B2 to attenuating networks of metal rectifiers M1. M2 and M3, M4 in the transmission and control paths, a circuit C1, R1 of suitable time constant being included in the control path. The characteristic of the control depends on the initial bias voltages and may also be varied by controlling the ratio of control current passing to the two networks. Normally, the attenuation in the transmission path is small and that in the control path large, the attenuators being inversely controlled. The expander shown in Fig. 1b is similar but is controlled from the output side and both attenuators are normally of high impedance, a common bias battery being employed. Instead of networks in a loop circuit between transformers, the networks may be associated with a third winding of a transformer, Fig. 2 (not shown). Figs. 3a and 3b (not shown) comprise a compressor and expander in which shunt non-linear impedances are used in the transmission path and series impedances in the control path and vice-versa, the transmission and control paths being decoupled by resistance-capacity connections. The characteristics of the attenuators are such that a linear compression or expansion and a non- distorted overall characteristic is produced.