find_thresh_cross

 [onsets, offsets] = find_thresh_cross(data,params);

 Returns vectors containing the sample indices at which
 threshold values in the data vector were crossed. Will return both onsets and
 offsets. 

 params is a structure that governs how the threshold crossings are found

 .thresh - value that must be matched or exceeded
 .dir - direction to look at. If 'pos', then the algorithm look for values
        that are more positive than the threshold value. If it is 'neg' then
        the algorithm looks for values that are more negative than the
        threshold value.
 .remove_mean - if true, the mean is removed from the data before the
        thresholds are found. Note that the threshold value refers to the
        zero-mean data.

0001 function [onsets, offsets] = find_thresh_cross(data,params)
0002 % [onsets, offsets] = find_thresh_cross(data,params);
0003 %
0004 % Returns vectors containing the sample indices at which
0005 % threshold values in the data vector were crossed. Will return both onsets and
0006 % offsets.
0007 %
0008 % params is a structure that governs how the threshold crossings are found
0009 %
0010 % .thresh - value that must be matched or exceeded
0011 % .dir - direction to look at. If 'pos', then the algorithm look for values
0012 %        that are more positive than the threshold value. If it is 'neg' then
0013 %        the algorithm looks for values that are more negative than the
0014 %        threshold value.
0015 % .remove_mean - if true, the mean is removed from the data before the
0016 %        thresholds are found. Note that the threshold value refers to the
0017 %        zero-mean data.
0018 
0019 % 07/20/06 Petr Janata
0020 
0021 % Check for input arguments
0022 error(nargchk(2,2,nargin))
0023 
0024 onsets = [];
0025 offsets = [];
0026 
0027 % Make sure we have the required fields in the parameter structure
0028 if ~isfield(params,'dir'), myfprintf('Missing .dir field\n'), return, end
0029 if ~isfield(params,'thresh'), myfprintf('Missing .thresh field\n'), return, end
0030 
0031 % Check to make sure that we are dealing with a vector
0032 dims = size(data);
0033 if all(dims > 1), myfprintf('Input must be a vector'), return, end
0034 
0035 data = data(:);
0036 
0037 % Remove the mean if desired
0038 if isfield(params,'remove_mean') && params.remove_offset
0039   data = data-mean(data);
0040 end
0041 
0042 switch params.dir
0043   case {'pos','positive'}
0044     mask = data >= params.thresh;
0045   case {'neg','negative'}
0046     mask = data <= params.thresh;
0047   otherwise
0048     myfprintf(sprintf('Unknown direction: %s', params.dir));
0049     return
0050 end
0051 
0052 diff_vect = diff(mask);
0053 onsets = find(diff_vect == 1)+1;
0054 offsets = find(diff_vect == -1)+1;
0055 
0056 function myfprintf(msg)
0057   fprintf('find_thresh_cross: %s\n', msg);
0058   return
0059