Use of the Butterworth Filter Option

Use of the Butterworth Filter Option

The Butterworth filter is a low pass filter with two input variables; order and cut-off frequency.

The order of the filter controls the roll-off rate, as shown here in the figure (right) This is a 300Hz filter. It can be seen that higher orders attenuate the results more quickly: they have a higher roll-off rate.

The cut-off frequency is the frequency at which the gain of the filter is -3dB (i.e. the magnitude of signals at this frequency is halved by the filter). The lower the frequency the less noise passes through; but any peaks in the signal tend to get reduced in magnitude and delayed in time.

The above figures show examples of filtering frequency using the four standard SAE filters (60, 180, 600 and 1000 Hz cut-off frequencies: see below). These show clearly how the original signal is smoothed.