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reference:ft_preproc_highpassfilter [2018/08/23 14:43] (current)
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 +Note that this reference documentation is identical to the help that is displayed in MATLAB when you type "help ft_preproc_highpassfilter"​.
 +  <a href=/​reference/​ft_preproc_highpassfilter><​font color=green>​FT_PREPROC_HIGHPASSFILTER</​font></​a>​ applies a high-pass filter to the data and thereby removes
 +  the low frequency components in the data
 +  Use as
 +    [filt] = ft_preproc_highpassfilter(dat,​ Fsample, Fhp, N, type, dir, instabilityfix)
 +  where
 +    dat        data matrix (Nchans X Ntime)
 +    Fsample ​   sampling frequency in Hz
 +    Fhp        filter frequency
 +    N          optional filter order, default is 6 (but) or dependent upon
 +               ​frequency band and data length (fir/firls)
 +    type       ​optional filter type, can be
 +                 '​but'​ Butterworth IIR filter (default)
 +                 '​firws'​ windowed sinc FIR filter
 +                 '​fir'​ FIR filter using MATLAB fir1 function
 +                 '​firls'​ FIR filter using MATLAB firls function (requires MATLAB Signal Processing Toolbox)
 +                 '​brickwall'​ Frequency-domain filter using MATLAB FFT and iFFT function
 +    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 except for firws)
 +                 '​twopass-reverse'​ zero-phase reverse and forward filter
 +                 '​twopass-average'​ average of the twopass and the twopass-reverse
 +                 '​onepass-zerophase'​ zero-phase forward filter with delay compensation (default for firws, linear-phase symmetric FIR only)
 +                 '​onepass-reverse-zerophase'​ zero-phase reverse filter with delay compensation
 +                 '​onepass-minphase'​ minimum-phase converted forward filter (non-linear!,​ firws only)
 +    instabilityfix optional method to deal with filter instabilities
 +                 '​no' ​      only detect and give error (default)
 +                 '​reduce' ​  ​reduce the filter order
 +                 '​split' ​   split the filter in two lower-order filters, apply sequentially
 +    df         ​optional transition width (firws)
 +    wintype ​   optional window type (firws), can be
 +                 '​hann' ​                (max passband deviation 0.0063 [0.63%], stopband attenuation -44dB)
 +                 '​hamming'​ (default) ​   (max passband deviation 0.0022 [0.22%], stopband attenuation -53dB)
 +                 '​blackman' ​            (max passband deviation 0.0002 [0.02%], stopband attenuation -74dB)
 +                 '​kaiser'​
 +    dev        optional max passband deviation/​stopband attenuation (firws with kaiser window, default = 0.001 [0.1%, -60 dB])
 +    plotfiltresp optional, '​yes'​ or '​no',​ plot filter responses (firws, default = '​no'​)
 +    usefftfilt optional, '​yes'​ or '​no',​ use fftfilt instead of filter (firws, default = '​no'​)
 +  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.
 +  Further note that the filter type '​brickwall'​ filters in the frequency domain,
 +  but may have severe issues. For instance, it has the implication that the time
 +  domain signal is periodic. Another issue pertains to that frequencies are
 +  not well defined over short time intervals; particularly for low frequencies.
 +  See also PREPROC