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.
 |
resonant peak frequency,
natural frequency of the undamped
oscillation; 
on logarithmic scale)