shown in fig7 has an oscillator circuit 58 that has an oscillation frequency of for example 300 khz to 1 mhz the signal generated by the oscillator circuit 58 is coupled through a capacitor c 3 formed out of two metal plates 54 and a metalized area 38 on the tape 36 thus the two metal plates 54 and the metalized area 38 of the tape form a capacitive couple between the oscillator 58 and the output 64 when the metalized area 38 completely overlaps the two metal plates 54 the signal is most efficiently transmitted between the oscillator circuit 58 and the positive input 60 of the operational amplifier 62 of the circuit 56 when a metalized area 38 only partially overlaps the metal plates 54 or is completely absent the transmitted signal decreases or reaches a minimum thus the amplitude of the signal received from the oscillator circuit 58 varies with the speed at which the tape is moving past the capacitor c 3 the output 64 of the operational amplifier 62 is rectified by diode d 1 supplying a pulsed dc output which has frequency which is directly proportional to the speed at which the tape 36 is being withdrawn from the cartridge 42 still another approach to detecting the speed of the tape 36 as it is withdrawn from a cartridge 65 is based on the metalized regions 38 being formed of a magnetically.