GB1371964A - Audio reproduction apparatus - Google Patents

Abstract

1371964 Data storage and retrieval WESTINGHOUSE ELECTRIC CORP 16 June 1972 [30 July 1971] 28244/72 Heading G4H In a system for data recording and retrieval on audio media (e.g. a tape recorder), each data signal consists of a subaudible (40 Hz) tone followed by binary data in the form of widthmodulated 3kHz tone bursts separated by 2 kHz tone bursts (Fig. 5). Data is recorded on a tape recorder B by the apparatus of Fig. 2, wherein the binary values are entered on switches 1, and a switch 2 is pressed to set a bi-stable 3 (which enables a gate 21 via a latch 22) and trigger a monostable 4, whereby a multiplexer 5 accepts the output of a zero crossing detector 7 connected to a 40 Hz oscillator 8. While 4 outputs a "1", the output from 7 ensures that latch 22 enables gate 21 and that a latch 6 outputs a signal to cause a multiplexer 9 to pass the 40 Hz tone to recorder B. When the output from 4 reverts to "0", multiplexer 5 feeds the output from a 2-3 kHz zero crossing detector 20 to latch 22 and the output from 6 changes to cause multiplexer 9 to accept 2 kHz signals from an oscillator 14. The output change from 6 also triggers a monostable 10 which starts a twoperiod clock 11 when its output reverts from "1" to "0": when the clock starts, its "1" output causes a latch 16 to change to "1", whereby a capacitor C4, Fig. 4 (not shown), is switched into an R.C. circuit in 14 to change its frequency to 3 kHz (when its output becomes "0" again (C4) is removed and the output from 14 changes to 2 kHz again). A 90 degree phase shift and zero cross detector 15 controls latch 16 to ensure smooth 2-3 kHz transitions. The clock period (i.e. duration of its "1" outputs) is determined by a multiplexer 13 which scans switches 1 and switches a resistor R1 into and out of the clock circuit: the period is 8 or 16 msec. according as 13 detects a "0" or a "1" at the switches. At the end of the data (determined by a counter 12 and comparator 18) a monostable 19 is triggered: 14 supplies a 2 kHz "end" signal until 19 turns off and resets bi-stable 3. The tape B is read by a tone code reader (Fig. 6, not shown) wherein detection of the 40 Hz signal disconnects a listener speaker from the recorder while the 2/3 kHz tone bursts are being filtered and rectified: these latter are fed to a comparator (60) whose output (1=2 kHz, 0= 3 kHz) provides clock signals for a shift register (63). A 3 kHz time comparator (61) determines the binary nature of each bit which is stored in (63), and a 2 kHz time comparator (65) detects the "end" signal to terminate the retrieval process.