function output=diffrect(sig,nbands)
% DIFFRECT differentiates a signal, then half-wave rectifies the
% result.
%
% DIFF = DIFFRECT(SIG, NBANDS) takes in a time domain signal
% stored in a vector with each column representing a different
% frequency band. The number of frequency bands is passed in
% through NBANDS.
%
% Defaults are:
% NBANDS = 6
%
% This is the third step of the beat detection sequence.
%
% See also FILTERBANK, HWINDOW, and TIMECOMB
if nargin <2, nbands=6; end
n = length(sig);
output=zeros(n,nbands);
for i = 1:nbands
for j = 5:n
% Find the difference from one smaple to the next
d = sig(j,i) - sig(j-1,i);
if d > 0
% Retain only if difference is positive (Half-Wave rectify)
output(j,i)=d;
end
end
end