What is the difference between disturbance rejection and using a simple filter?

Shreesh P. Mysore, 14 Oct 02

In disturbance rejection, one wants to design the controller so that the system is insensitive to frequencies (s) above a certain value (for instance). This would involve the same ideas as when designing a filter. The controller needs to do this, while also simultaneously making sure that other criteria (like attaining the reference value) are met.