GB732370A - Improvements in or relating to electrical systems for the transmission of speech - Google Patents

Abstract

732,370. Secret telephony. GENERAL ELECTRIC CO., Ltd., and BLOCH, A. Aug. 7, 1953 [July 31, 1952], No. 19413/52. Class 40 (4). In a speech-transmission system in which frequency-compression is achieved by taking samples of the speech and transmitting them at reduced speed, the frequency of sampling is adjustable. As shown (Fig. 1) a transmitting terminal comprises a plurality of devices 1 for effecting frequency-compression of an input speech signal supplied over a path 2. Each of the devices 1 comprises (Fig. 2) a continuous magnetic tape 5 on which the speech signal is recorded by means of a recording head 6. A drum 9 carrying a plurality of pick-ups 8 rotates so that the speed of each pick-up 8 is less than that of the tape 5. The pick-ups 8 thus take samples of the recorded speech and transmit them at reduced speed through a variable attenuation network or variable-gain amplifier 12 which fades each pick-up in and out in turn. The recorded speech is erased by a head 13. The various devices 1 have different sampling frequencies, and the device having the sampling frequency nearest to the fundamental frequency of the input speech at any moment is selectively brought into operation by means of filters 15, 16 and relays A, B, C ... (Fig. 1). A similar arrangement at the receiving terminal effects frequency-expansion, so that a speech signal is reproduced having approximately the same pitch as the input speech signal.