function y = ppsrc(x,h,L,M);

% Synopsis:  y = ppsrc(x,h,L,M).

% Sampling-rate conversion by polyphase filters.

% Input parameters:

% x: the input sequence

% h: the conversion filter

% L, M: the interpolation and decimation factors.

% Output parameters:

% y: the output sequence



% Part of software package for the book:

% A Course in Digital Signal Processing

% by Boaz Porat, John Wiley & Sons, 1997



ML = M*L; lh = length(h); lx = length(x);

ly = floor((L*lx+lh-2)/M)+1; % length of the result

K = floor((lh-1)/ML)+1; % max length of polyphase components

r = zeros(ML,K); % storage for polyphase components

for l = 0:L-1, % build polyphase components

for m = 0:M-1,

   temp = h(rem(l*M+(M-m)*L,ML)+1:ML:lh);

   if (length(temp) > 0),

   r(M*l+m+1,1:length(temp)) = temp; end

end, end

x = [reshape(x,1,lx),zeros(1,M)]; % needed for the 1 delay

lx = lx + M;

lu = floor((lx-1)/M) + 1; % length of the sequences u_m

x = [x, zeros(1,M*lu-lx)];

x = reshape(x,M,lu); % now the rows of x are the u_m

y = zeros(L,K+lu-1);

for l = 0:L-1, % loop on sequences v_l

for m = 0:M-1, % loop on sequences u_m

   if (m <= floor(l*M/L)),

      temp = x(m+1,:);

   else

      temp = [0,x(m+1,1:lu-1)];

   end

   y(l+1,:) = y(l+1,:) + conv(r(M*l+m+1,:),temp);

end, end

y = reshape(y,1,L*(K+lu-1));

y = y(1:ly);