Transition band

This is the area between where a filter "turns the corner" and where it "hits the bottom".

An example of this can be taken from a low-pass filter, commonly used in audio systems to allow the bass signal to pass through to a subwoofer, and cut out all unwanted frequencies above a defined point.

The transition band can be implemented to allow for a smooth fall off to avoid introducing audible peaks in amplitude.

The curve that the transition band follows depends on the engineering of the filter, including component reaction time and the choice of values for the components that comprise the filter according to mathematical formula.

This can be of general importance when calculating the values required for filters used in the control of signal transmission systems, to ensure that the entire bandwidth of the desired signal is allowed to pass.