Another common application is medical instrumentation, where high-impedance sensors pick up line frequencies. Definitions for center frequency, bandwidth, and selectivity are the same as for band-pass versions. This is also called the Bode plot. Phase response is the phase shift of the output relative to the input. Delay is the time lag between the input and the output .
Real filters are far from ideal.
Constructed from actual electronic components, they subject input signals to mathematical transfer functions that only approximate ideal behavior.