GB1409799A - Quality system for a bandlimited voice signal - Google Patents

Abstract

1409799 Band limited transmission system KOKUSAI DENSHIN DENWA KK 21 Sept 1972 [23 Sept 1971 25 Oct 1971] 43686/72 Heading H4R In a quality improving system for a bandlimited voice signal, a received band limited signal is branched at a hybrid 4 (Fig. 1) and one of the branched signals is applied to an arrangement of an instantaneous compressor 7 and frequency expander 8 arranged in cascade and forming a higher harmonic signal generator, the output e3(t) of which is applied to a band pass filter passing the higher harmonics, which higher harmonics are then combined with the amplified other branched signal. Such an arrangement is designed to increase the band width from 0À3 to 1À5 kHz to 0À3 to 3.4 kHz. Figs. 2 and 3 show respectively examples of an instantaneous compressor having a compression ratio of ¢ and an expander having a square expansion coefficient and which also full wave rectifies the waveform, thereby introducing the higher harmonics. This is also described in the Specification the application of the arrangement of Fig. 1 to a radio telephone receiver, to radio terminal equipment of the dincompex type, and to a telecommunication system in which a telephone signal and a " stroke signal "as transmitted in respective halves of the frequency band, (Figs. 5-8, not shown). Fig. 9 and Figs. 10-12 (not shown) illustrate a more complicated frequency expander for use in place of the arrangement of Fig. 3. The output of the instantaneous compressor 102(7) is used to phase modulate a signal of frequency #0 in phase modulator 103 which includes an oscillator of frequency #0. The output e3(t) of the phase modulator is applied to a frequency converter 104 which also has as an input an unmodulated signal e6(t) of frequency #0 provided by a synchronous oscillator 106 driven by a signal derived by a band pass filter 105 from the signal e3(t). The output of the frequency converter is passed through a low pass filter 107 to supply an output signal comprising higher harmonics of the input signal at terminal 101, the harmonics being either even or odd (but not both). If both odd and even harmonics are required a second frequency converter and low pass filter are supplied in parallel with converter 104 and filter 107, the synchronous oscillator 106 supplying the signal e6(t) to the second frequency converter via a 90-degree phase shifter (Fig. 10, not shown). The band pass filter and synchronous oscillator may be replaced by a single oscillator of frequency #0 which drives both the phase modulator 103 and the frequency converters (Figs. 11 and 12, not shown). Fig. 13 shows an arrangement where one of the branched signals is further branched into a number of frequency bands and a higher harmonic generator is applied for each frequency band. The higher harmonics produced for each frequency band are then weighted before being combined. The Specification contains a mathematical analysis of the operation of the circuits.