GB859602A - Improvements in or relating to apparatus for effecting amplitude compression or expansion of electric signals - Google Patents

Abstract

859,602. Volume compression and expansion. GENERAL ELECTRIC CO. Ltd. July 14, 1959 [April 14, 1958], No. 11847/58. Class 40 (4). Several channels share a single compressor or expander on a time-division bases. As shown, signals are fed to the compressor 2 from channels 1A, 1B ... in succession by an electronic switch 5, whence they are distributed to the channels 3A, 3B ... by switch 6. Each output channel feeds a low-pass filter 7 and detector 8 which produces a signal following the syllabic changes of level. These are fed by switch 9 at the appropriate instant to the compressor 2 to effect the compression appropriate to that channel. Since the intelligence of any output channel is available either in the audio range or as side-bands of the switching frequency or its harmonics these may be selected by appropriate different filters for the different channels, and combined for frequency multiplex transmission. Alternatively identical filters 10 may select the same side-band, say 8-12 kc/s., which may then be fed to modulators 11 fed by appropriate frequencies, and filtered at 12 for combination in the frequency multiplex transmission line 13. By so choosing such a side-band rather than the audio signal, the construction of the filters 12 is simplified. Supervisory signals may be injected at 14. An expander operating on the same principles, but with the control signals for the expander being derived from the input signals is also described, Fig. 2 (not shown). Separate signals indicating the degree of compression may be sent if desired.