An important term that has not been defined so far is the bandwidth of a system. Lag elements with a proportional behaviour, e.g. , and elements as well as elements ( elements in series connection), show a so-called low-pass property. This means that they pass low frequencies whereas high frequencies in signals are attenuated by the strongly decreasing amplitude response of the frequency response. In order to describe this behaviour the concept of bandwidth is introduced. This is the frequency at which the magnitude of the frequency response is decreased by 3dB from the value of the initial horizontal asymptote, see Figure 4.19.