low pass filter the circuit for the operational amplifier v2 is similar and its output is connected to the other input of the comparator v3 the output of the comparator is available at terminal a and is a binary output signal having one or another voltage level depending on which of the two operational amplifiers v1 and v2 has a greater output the attenuators are controlled in accordance with the control signal available at terminal a by conventional means the time constant of the speech direction recognition circuit is determined by the resistor r3 and the capacitor c1 the delay time is determined by the values of the capacitor c1 and the resistors r2 and r3 the gain of the amplifiers is determined by the ratio of the resistors r1 and r2 the bias circuit incorporates an operational amplifier v4 the inverting input of which is connected to a terminal eh to which is supplied a height regulating voltage the non inverting input of the amplifier v4 is connected to the tap of a potentiometer p2 which establishes a bias on the amplifier v4 the output of the amplifier v4 is connected by a diode d2 and a resistor r6 to the non inverting input of the amplifier v1 and also to one end terminal of a potentiometer p1 the other end terminal of the potentiometer p1 being connected to the.