Filter

Filter options.

Options for low-pass, high-pass, bandpass and bandstop modes with Bessel and Butterworth filters are provided.

Zero-phase shift filtering is achieved by passing the data forwards and backwards through a linear digital filter. This process doubles the effective order of the filter, and this is accounted for in the Filter options menu. For example, if an 8^th order Bessel is specified, a 4^th order filter is designed and the data passed through twice for an effective filter order of 8.

Convenient interfaces are provided for checking the results of filtering before applying to the data. The See Filtered Data button will display the currently selected trace overlaid with the filtered trace in red. Show FFT will show the Fourier-transformed data, with the power-spectrum of the filter data overload in red. Finally, clicking Apply will filter all records in the file.

Filter Data. Data are low-pass filtered at \(1000\ \mathrm{Hz}\) using an eighth-order Bessel filter. See Filtered Data overlays the filtered trace for inspection before applying the filter.