Constructs a smoothing filter

Wrapper function for gsignal::butter to construct a bandpass (or low or high pass) filter at a particular frequency. Uses the Sos form for the filter, which works better numerically particularly for very low frequencies.

Usage

build_filter(lo = NULL, hi = NULL, sampfreq, order = 13)

Arguments

lo

Lower frequency cutoff in Hz. If only lo is specified, then build_filter constructs a high pass filter

hi

Upper frequency cutoff in Hz. If only hi is specified, then build_filter constructs a high pass filter

sampfreq

Sampling frequency for the data in Hz.

order

(optional) Order for the filter

Value

Filter parameters in Sos form

Examples

# Low pass filter with a cutoff at 0.5Hz for data sampled at 100Hz
lopass <- build_filter(lo=0.5, sampfreq=100)

# Band pass filter that passes frequencies between 0.5 and 10Hz
bandpass <- build_filter(lo=0.5, hi=10, sampfreq=100)