Patent GB-1113223-A (GB)
Title: Improvements in or relating to electric selective signalling systems
Inventor: GILL JOHN STEWART
IPC: G10L25/93
Filed: 1964-09-15
Abstract: 1,113,223. Excitation function generation. MINISTER OF TECHNOLOGY. 6 Sept., 1965 [15 Sept., 1964], No. 37596/64. Heading H4R. [Also in Division G4] Unreliable measurements in a sequence of measured values of a variable are replaced by measurement values interpolated or extrapolated from adjacent measurement values. The variable may be the period between adjacent pulses of excitation function of a speech signal derived by the apparatus of Specification 1,113,224. Embodiments are described for both analogue and digital signals. In Fig. 4 successive digital signals from a larynx excitation period detector are fed via input lines I1 into the shift register S1 to S5. The signals are six digit binary numbers representing measurements of the larynx excitation period with the number 000000 representing no measurement and the number 000001 representing an unreliable measurement. The signals are passed sequentially through the stages of the shift register under the control of signals on the line 13, each number being held for 20 millisecs. in each storage location. In each storage location the binary number is applied to an analogue to digital converter DA1-DA5 and also the five most significant digits are applied to an " or " gate G11 to G15 so that only if there is a " one " in at least one of the first five digit positions of the number is the respective gate G1 to G5 opened to allow the analogue value, corresponding to the digital number in the respective stage of the register, to be applied to the corresponding terminal 1 to 5 of the resistance matrix including the resistors " r " and the resistors R1 to R5. The resistive matrix is such that the voltage appearing on line 6 is weighted toward the voltage appearing at point 3 of the matrix. If a valid signal is stored in stage S3 of the register then the voltage on line 6 will be substantially equal to the value stored in stage S3 and fed through gate G3. If the signal stored in stage S3 is not a valid number, e.g. does not contain a " 1 " in any of the first five digit places, gate G3 is not opened and the value appearing at point 3, and fed to line 6, will be an interpolation or extrapolation of the values fed to adjacent points of the matrix. The resulting waveform on line 6 is filtered by low-pass filter F and fed to the utilization or transmission device via a gate G6. The gate G6 is arranged to inhibit the transmission of the signal during each period of occurrence of no measurement. Since the filter F introduces a 20 millisecs. delay in the output signal of the apparatus the gate is inhibited whenever the signal 000000 appears in stage S4 of the shift register by a signal provided by the " OR gate G8. In addition " NOR " gates G21 to G25 together with gates G26 and G27 inhibit the output whenever there is no " 1 " in any of the first five digit positions of any of the stages of the shift register, i.e. there is no valid signal in the shift register from which an interpolation or extrapolation may be made. An alternative logical arrangement which eliminates the gates G21 to G25 by using the outputs of gates G11 to G15 and an " OR " gate (G7) is described with reference to Fig. 5 (not shown). An arrangement in which analogue values are stored in the shift register is described with respect to Fig. 1 (not shown), in which the gates (G1 to G5) are operated by control signals derived by a circuit which discriminates between valid analogue measurement values, unreliable values, and no signal.