fir_filterdcpadded.m

% fir_filterdcpadded() - Pad data with DC constant and filter
%
% Usage:
%   >> data = fir_filterdcpadded(b, a, data, causal, usefftfilt);
%
% Inputs:
%   b             - vector of filter coefficients
%   a             - 1
%   data          - raw data (times x chans)
%   causal        - boolean perform causal filtering {default 0}
%   usefftfilt    - boolean use fftfilt instead of filter
%
% Outputs:
%   data      - smoothed data
%
% Note:
%   fir_filterdcpadded always operates (pads, filters) along first dimension.
%   Not memory optimized.
%
% Author: Andreas Widmann, University of Leipzig, 2014

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% Copyright (C) 2013 Andreas Widmann, University of Leipzig, widmann@uni-leipzig.de
%
% This program is free software; you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation; either version 2 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program; if not, write to the Free Software
% Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
%
% $Id$

function [ data ] = fir_filterdcpadded(b, a, data, causal, usefftfilt)

% Defaults
if nargin < 5 || isempty(usefftfilt)
    usefftfilt = 0;
end
if nargin < 4 || isempty(causal)
    causal = 0;
end

% Check arguments
if nargin < 3
    error('Not enough input arguments.');
end

% Is FIR?
if ~isscalar(a) || a ~= 1
    error('Not a FIR filter. onepass-zerophase and onepass-minphase filtering is available for FIR filters only.')
end

% Group delay
if mod(length(b), 2) ~= 1
    error('Filter order is not even.');
end
groupDelay = (length(b) - 1) / 2;

% Filter symmetry
isSym = all(b(1:groupDelay) == b(end:-1:groupDelay + 2));
isAntisym = all([b(1:groupDelay) == -b(end:-1:groupDelay + 2) b(groupDelay + 1) == 0]);
if causal == 0 && ~(isSym || isAntisym)
    error('Filter is not anti-/symmetric. For onepass-zerophase filtering the filter must be anti-/symmetric.')
end

% Padding
if causal
    startPad = repmat(data(1, :), [2 * groupDelay 1]);
    endPad = [];
else
    startPad = repmat(data(1, :), [groupDelay 1]);
    endPad = repmat(data(end, :), [groupDelay 1]);
end

% Filter data (with double precision)
isSingle = isa(data, 'single');

if usefftfilt
    data = fftfilt(double(b), double([startPad; data; endPad]));
else
    data = filter(double(b), 1, double([startPad; data; endPad])); % Pad and filter with double precision
end

% Convert to single
if isSingle
    data = single(data);
end

% Remove padded data
data = data(2 * groupDelay + 1:end, :);
 
end