u03b8 represents the relative position between the resistive screw and the input probe according to the direction termed f 2 in fig2 consequently it can be appreciated that the resistive screw of the equaliser of fig1 produces an attenuation effect in which the ends of said frequency band experience greater attenuation in comparison with the central part of said frequency band the frequency response so obtained is that which serves to achieve the amplitude equalisation of the signal it is to be pointed out however that the resistive tuning means 5 can change position in two directions whereby a first change in position is in the direction of a plane substantially perpendicular with respect to the input signal injection means 6 for example by turning the resistive screw to bring it closer to the probe and a second change in position is in the direction of a plane substantially parallel with respect to the input signal injection means 6 said first and second changes in position are illustrated in fig2 by means of the arrows f 1 and f 2 respectively the first change in position permits adjustment of the response of the equaliser with regard to the magnitude of the resistive effect on the frequency response of the equaliser on the other hand the position of the resistive tuning means 5 in a plane substantially parallel with respect to the input signal injection means 6 determines the degree of symmetry between the ends of the response curve in the aforementioned frequency band as a result the second change in.