On systems that correspond to a 1st degree differential equation, the corner frequency is the intersection of the horizontal asymptote with the asymptote on the falling branch in a Bode diagram (see amplitude response). At this point the amplitude response is 3 dB and the phase shift 45°. This means that the reduction in the amplitude of the output variable has reached 30 % of the input variable.
At the same time is the time constant of such a system.
