function Px = welch(x,L,over,win)
%WELCH	Spectrum estimation using Welch's method.
%----
%USAGE	Px = welch(x,L,over,win)
%
%	The spectrum of a process x is estimated using Welch's method
%	of averaging modified periodograms.
%
%	x   : input sequence
%	L   : section length 
%	over: amount of overlap, where 0<over<1, 
%	win : The window type 
%       	1 = Rectangular
%		2 = Hamming
%		3 = Hanning
%		4 = Bartlett
%		5 = Blackman
%
%	Welch's estimate of the power spectrum is returned in Px 
%	using a linear scale.
%
%  see also BART, MPER, PER, and SPER
%
%---------------------------------------------------------------
% copyright 1996, by M.H. Hayes.  For use with the book 
% "Statistical Digital Signal Processing and Modeling"
% (John Wiley & Sons, 1996).
%---------------------------------------------------------------

if (nargin <= 3) win=1; end;
if (nargin <= 2) over=0; end;
if (nargin == 1) L=length(x); end
if (over >= 1) | (over < 0)  
   error('Overlap is invalid'), end
n1 = 1;
n2 = L;
n0 = (1-over)*L;
nsect=1+floor((length(x)-L)/(n0));
Px=0;
for i=1:nsect
    Px = Px + mper(x,win,n1,n2)/nsect;
    n1 = n1 + n0;  
    n2 = n2 + n0;
    end;