There are multiple types of filters, including Gimble Killer (which deals with strange rotations of joints that occur when MotionBuilder misinterprets the value of a rotation...for instance a 90 degree rotation can be misinterpreted as -270 degrees, which will cause the joint to rotate in the wrong direction), Butterworth (which removes frequency and removes dents or awkwardities to a curve), the Key Reducer (which, true to its namesake, reduces the keys on the selected portion of a curve), etc.
However, for this particular demo, I will be outlining use of the Smooth filter, as I commonly work with it more then other filters while editing animations.
The first step in using any filter is to select the portion of animation data that the filter is to be applied to; in this instance I chose to select every curve for every joint on an animated skeleton in their entirety to maximize visual information.
Once the area of the curve is specified, it is a matter of determining how strong an influence the smoothing filter will have, specified by the width value in the filters tab. From there, click preview to see the effects on the curve, and either reset and change values as necessary, or accept to have the filter permanently applied to the animation curve.
The first series of images below details the progression of the original curves of an animation as they are smoothed down through use of a Smooth filter with a width of 4.
The next series details use of a Smooth filter with a doubled width value of 8. As can be seen, the stronger the width, the smoother the curve, and the smaller the number of necessary filter applications.
