function Zx = stzerocross(x,N)%  stzerocross --> Short-term zero crossing measure using a sliding window.%%  <Synopsis>%    Zx = stzerocross(x,N)%%  <Description>%    An initial short-term zero crossing measure Zx(N+1) based on the%    (N+1)-sample vector x(1:N+1) is updated with the new sample x(N+2)%    and downdated with the oldest sample x(1), resulting in Zx(N+2).%    This update procedure of the short-term zero crossing estimate%    continues until the sliding window has reached the end of the%    signal x.%  <References>%  [1] J.R Deller, J.G. Proakis and F.H.L. Hansen, "Discrete-Time%      Processing of Speech Signals", IEEE Press, p. 245, (2000).%%  <Revision>%    Peter S.K. Hansen, IMM, Technical University of Denmark%%    Last revised: September 30, 2000%-----------------------------------------------------------------------% Check the required input arguments.if (nargin < 2)  error('Not enough input arguments.')endif (N > length(x))  error('The window length N can not be longer than the sequence length.')end% Make sure that x is a column vector.x = x(:);% Number of estimates to make.M  = length(x);Zx = zeros(M,1);% First zero crossing estimate.Zx(1:N+1) = sum(abs(sign(x(2:N+1)) - sign(x(1:N))))/(2*N);% Updating of the zero crossing estimate.for (m=(N+2):M)  Zx(m) = Zx(m-1) + (abs(sign(x(m)) - sign(x(m-1))) ...                  -  abs(sign(x(m-N)) - sign(x(m-N-1))))/(2*N);end%-----------------------------------------------------------------------% End of function stzerocross%-----------------------------------------------------------------------