Integration is the mathematical operation that is the inverse of differentiation. In vibration analysis, integration will convert an acceleration signal into a velocity signal, or a velocity signal into a displacement signal. Integration can be done with excellent accuracy with an analogue integrator in the time domain or can be done digitally in the frequency domain. For this reason, an accelerometer is the transducer of choice because velocity and displacement can be so easily derived from its output. An analogue integrator is actually a low-pass filter with 6 dB of attenuation per octave. This is true of an analogue integrator only above its low cut-off. And since the low cut-off cannot be zero, analogue integrators have low-frequency limits, usually either 1 or 10 Hz.