Smooth Filter (Butterworth) options

Note: Previous versions of Maya referred to this filter as Butterworth Filter. It has been renamed Smooth Filter (Butterworth) for clarity.

Smooth Filter (Butterworth) averages key frames using intelligent low-pass smoothing. It is a frequency filter that works best on curves affected by noise.

Smooth Filter (Butterworth) removes noise from data without affecting the curve's minimum or maximum values. In this way, Smooth Filter (Butterworth) avoids "over-averaging" problems that can happen when filtering motion capture data.
Note:

To restore the filter default settings, click Edit > Reset Settings in the Filter window.

Time Range

Specifies the time range where the curve is simplified.

All
Simplifies the curve for the entire time range.
Selection
Lets you select a portion of a curve, so you can apply the filter to a limited area, rather than affecting the entire curve. Hold Ctrl to select multiple areas at once.
Time Slider
Simplifies the curve for the time range defined by the Playback Start and End times of the Time Slider.
Start/End
All keys within the specified time range (start time/end time) are simplified.
Start Time

Specifies the start of the time range. This is available only if Start/End is on.

End Time

Specifies the end of the time range. This is available only if Start/End is on.

Preview
Lets you visualize the effect on your curve before you apply it. This option is on by default.
Cutoff Frequency
Lets you limit the strength of the filtering effect, allowing you to filter out high frequency noise.
Sampling Rate
Lets you set the density of the keys resampled at this rate.
Keep Keys on Frame
Lets you align keys with the frame rate
Preserve Keys by Tangent
Lets you exclude the selected tangent type(s) from filtering.