Butterworth filter tool: Butterworth band-pass filtering of traces
"Apply" - apply the filter with the current filter settings
"Low Freq: <nnn>" - displays low frequency corner (Hz), and accepts input of a new value
"High Freq: <nnn>" - displays high frequency corner (Hz), and accepts input of a new value
"Num Poles: <nnn>" - displays number of filter poles, and accepts input of a new value