In signal processing, a washout filter is a filter that makes a transition caused by changes in the input source more smooth. An example of this transition is the change in the modes of a signal. The general form of this filter is:
H(s) = s/(s+a)
The function of a filter like this, is to damp the DC part of a signal which is most useful for a signal that will be integrated in time afterwards. More information can be found under High-pass filter. It has been used in flight control stabilization. An example of this use of can be located at Yaw Damper Design for a 747® Jet.