FieldTrip

Note that this reference documentation is identical to the help that is displayed in Matlab when you type “help ft_preproc_lowpassfilter”.

  FT_PREPROC_LOWPASSFILTER applies a low-pass filter to the data and thereby
  removes all high frequency components in the data
  
  Use as
    [filt] = ft_preproc_lowpassfilter(dat, Fsample, Flp, N, type, dir)
  where
    dat        data matrix (Nchans X Ntime)
    Fsample    sampling frequency in Hz
    Flp        filter frequency
    N          optional filter order, default is 4 (but) or dependent upon
               frequency band and data length (fir/firls)
    type       optional filter type, can be
                 'but' Butterworth IIR filter (default)
                 'fir' FIR filter using Matlab fir1 function 
                 'firls' FIR filter using Matlab firls function (requires Matlab Signal Processing Toolbox)
    dir        optional filter direction, can be
                 'onepass'         forward filter only
                 'onepass-reverse' reverse filter only, i.e. backward in time
                 'twopass'         zero-phase forward and reverse filter (default)
 
  Note that a one- or two-pass filter has consequences for the
  strength of the filter, i.e. a two-pass filter with the same filter
  order will attenuate the signal twice as strong.
 
  See also PREPROC