FR1551882A - - Google Patents

Abstract

1,233,922. Vocoder. INTERNATIONAL BUSINESS MACHINES CORP. 19 June, 1968 [21 June, 1967], No. 29108/68. Addition to 1,233,462. Heading H4R. In apparatus for multiplexing the outputs of the vocoder analyser of parent Specification on to a telephone line the spectrum function output is peak detected to produce a signal having frequency components in the range 0-300 Hz which is modulated with a carrier of 1100 Hz and the upper side-band selected for transmission, the excitation function signal, comprising a base band signal in the range 300 to 800 Hz is transmitted unchanged, together with two pilot signals of 900 and 2000 Hz respectively from which the vocoder analyser synchronizing signal and the demodulator carriers are derived, the two frequencies being used so as to provide cancellation of frequency shift in the line, e.g. due to carrier working. Also described is a method of multiplexing the outputs of two vocoders on a single line. Fig. 1 shows a transmitter, including a vocoder analyser 4 of the type described with respect to Fig. 1 of the parent Specification. The excitation function signal, comprising a base band section of the speech signal in the band 300-800 Hz is fed direct to the line via adding circuit 19. The spectrum function signals are level detected in 5 and low-pass filtered in 6, modulated by an 1100 Hz carrier in 22, the upper sideband selected in 23 and applied to the adder 19 for transmission. The carrier for modulator 22 is derived from the difference signal between the 900 Hz pilot from oscillator 16 and the 2000 Hz pilot from oscillator 17. The 2000 Hz pilot is also divided to obtain a signal of 50 Hz to control the operation of the frequency shift circuit 13 in the vocoder analyser 4. At the receiver, Fig. 4, the carrier for demodulating the spectrum function signal selected by filter 29 is derived from the two pilots by deriving their difference signal in modulator 32 and filter 33. This difference frequency, 1100 Hz, is divided by 11 in 37, and multiplied by 2 in 38 to provide a 200 Hz signal which modulates the 900 Hz signal, received from the line, in 39 to produce an 1100 Hz signal which is applied via a filter 40 and phase shifter 41 to the modulator 42. Any frequency shift in the spectrum function signal received from the line is cancelled by the same frequency shift present in the 900 Hz signal applied to the modulator 39. The 1100 Hz signal from 33, from which frequency shift is eliminated since it is derived from the difference between two similarly shifted signals, is divided by two in 34, delay equalized in 35, and the resulting 550 Hz signal is applied to divider 36 where it is divided by eleven to produce a 50 Hz signal to synchronize the variable frequency oscillator 47. A similar system is described with respect to Figs. 6 and 7 (not shown) to derive carriers and synchronizing signals for the transmission by frequency multiplex of the outputs of two vocoder analysers.