GB1023974A - Improvements in or relating to recording systems or apparatus - Google Patents

Abstract

1,023,974. Local circuits for magnetic recording &c. apparatus; electric analogue calculating. COMMUNICATIONS PATENTS Ltd. Nov. 4, 1963 [Nov. 19, 1962], No. 43618/62. Headings G4G and G5K. [Also in Divisions H3 and H4] Variations in signals reproduced from a recording medium due to variations in speed of the medium are corrected by a correction signal derived from a constant frequency signal recorded on the medium. Referring to Fig. 2 the magnetic tape 30 carries eight tracks, a speech track 1, a reference track 4 containing a constant frequency square wave, and other tracks such as 2 containing a square wave frequency modulated in accordance with the data fed to the original recording circuit. The outputs from tracks 2 and 4 are fed to pulseshaping units 14 and 15 and then to monostable multivibrators 16 and 17 which produce negative pulses of uniform width at twice the input frequencies. These pulses are integrated in filters 18 and 19 to produce voltages V m and V, respectively. Errors in tape speed affect V m and V, in the same ratio and the voltage V r is used to correct V m . V m is used in unit 21 to modulate the pulse width of square wave pulses of constant frequency from a generator 20, the length T m of the pulses being inversely proportional to V m . V r amplitude modulates the pulses in unit 22 to give an output propor- V r tional to-, and this output is integrated by V m a filter 23 and passed through a D.C. amplifier 24 to an output device 26 which may be a voltmeter or a pen-type recorder. Electric analogue calculating.-In Fig. 3 a mono-stable multivibrator is triggered by a square wave input f 0 applied to terminal 60, and its timing capacitor 45 is discharged through a constant current generator 52 controlled by an input voltage V m at transistor 54. Thus the length T m of the negative-going part of the output pulses is inversely proportional to V m .-These pulses pass to a switching circuit, Fig. 4, wherein the output of transistor 74 is clamped to an input voltage V, for the pulse duration when the transistor is non-conducting. The output of transistor 74 passes to emitterfollower circuits 83 and 86 and comprises pulses of a width inversely proportional to V m and of an amplitude proportional to V r .-The final output may be integrated in a filter to produce a voltage proportional to V r /V m-