Butterworth filter

This function filters the data using a zero-phase butterworth filter. Either a band pass, band stop, high pass, or low pass filter can be implemented. The filter order is defined by the user. This function uses the Matlab butter and filtfilt functions.

EEGLAB user interface

1. Enter the frequencies for filtering.

2. Enter the order of the filter.

3. Select the filter type. For a band-pass filter, frequencies outside of the high and low pass cutoffs will be excluded, whereas for the band-stop filter, frequencies within the high and low pass cutoffs will be excluded. For a high-pass filter, frequencies below the cutoff will be excluded (note that low-pass field can be left blank), whereas for a low-pass filter, frequencies above the cuttoff will be excluded (note that high-pass field can be left blank).

Scripts

Base function

EEG = tesa_filtbutter( EEG, high, low, ord, type ); Default use.

Pop function

EEG = pop_tesa_filtbutter( EEG ); Pop up window

EEG = pop_tesa_filtbutter( EEG, high, low, ord, type ); Custom inputs

Required inputs

Input	Description	Example	Default
EEG	EEGLAB EEG structure	EEG	-
high	Integer setting the high pass frequency	1	-
low	Integer setting the low pass frequency	100	-
ord	Integer setting the filter order	4	-
type	String which sets the design of either a zero-phase band pass, band stop , high pass or low pass butterworth filter; string is either 'bandpass', 'bandstop', 'highpass', or 'lowpass'.	'bandpass'	-

Outputs

Output	Description
EEG	EEGLAB EEG structure

Examples

EEG = pop_tesa_filtbutter( EEG, 1, 100, 4, 'bandpass' ); Zero-phase, 4th-order band pass butterworth filter between 1-100 Hz.

EEG = pop_tesa_filtbutter( EEG, 48, 52, 4, 'bandstop' ); Zero-phase, 4th-order band stop butterworth filter between 48-52 Hz.

EEG = tesa_filtbutter( EEG, 1, [], 4, 'highpass' ); Zero-phase, 4th-order high pass butterworth filter allowing frequencies above 1 Hz

EEG = tesa_filtbutter( EEG, [], 45, 4, 'lowpass' ); Zero-phase, 4th-order low pass butterworth filter allowing frequencies below 45 Hz