n = (1:500).' ;
    s = exp(-((n-200).^2)/100^2) ;
    plot(n,s) ;             % slowly varying signal
        %
        % add noise in the stopband:
        %
    z = 0.3*cos(0.42*pi*n) + 0.1*cos(0.53*pi*n);
    x = s+z   ;
    plot(n,x)
    b = firpm( 36, [0.0 0.12 0.15 0.5]*2, [1 1 0 0] )
    y = filter(b,1,x) ;     % run filter on x
    plot(n,y)
    hold
    plot(n,s)               % note delay