erp.easy (version 1.0.0)

erp.filter: Filter ERP data using a Butterworth filter from the "signal" package

Description

erp.filter Using the "signal" package, erp.easy data frames can be filtered with a variety of Butterworth filters.

Usage

erp.filter(data, freq, ftype = "low", order = 4)

Arguments

data

A data frame in the format returned from load.data

freq

A value between 0 and 1 specifying the cutoff frequency (the erp.easy adapted function supports digital filters only, where 1 is the Nyquist frequency). For example, for a sampling rate of 1000 Hz, a cutoff value of 12 Hz would be designated as 0.012 (12 / 1000). A cutoff value of 8 Hz would be 0.008 (8 / 1000).

ftype

The type of filter to be used: values include: high-pass ("high"), low-pass ("low"), stop-band ("stop"), and pass-band ("pass"). The default is set to "low."

order

The complexity, or "order" of the Butterworth filter. The default value is a 4th order filter (24 dB/octave).

Value

A data frame identical to the original data frame, but with filtered amplitudes.

Details

See signal package reference manual for detailed instructions for using the butter function.

Examples

# Low pass filter ERP data (sampled at 250 Hz) with a cutoff frequency of 8 Hz
filtered <- erp.filter(ERPdata, freq = 0.032, ftype = "low", order = 4)
grandaverage(filtered, "V78", window = c(1000, 1500))