Carry out the overlap-add FFT processing:

y = zeros(1,Nsig + Nfft); % allocate output+'ringing' vector
for m = 0:(Nframes-1)
    index = m*R+1:min(m*R+M,Nsig); % indices for the mth frame
    xm = sig(index);  % windowed mth frame (rectangular window)
    xmzp = [xm zeros(1,Nfft-length(xm))]; % add zero to the signal
    Xm = fft(xmzp);
    Ym = Xm .* H;               % freq domain multiplication
    ym = real(ifft(Ym))         % fft inverse transform
    outindex = m*R+1:(m*R+Nfft); % out indices
    y(outindex) = y(outindex) + ym; % recovering a signal
end