help in getting the matlab output using the fdatool

hi.. im designin fir lowpass filter using fdatool... now i got the response n i generated the m file to see my specification which is shown below...

function Hd = fir1
%FIR1 Returns a discrete-time filter object.

%
% M-File generated by MATLAB(R) 7.3 and the Signal Processing Toolbox 6.6.
%
% Generated on: 09-Mar-2011 21:56:57
%

% Equiripple Lowpass filter designed using the FIRPM function.

% All frequency values are in Hz.
Fs = 48000; % Sampling Frequency

Fpass = 11000; % Passband Frequency
Fstop = 12000; % Stopband Frequency
Dpass = 0.17099735734; % Passband Ripple
Dstop = 0.00056234132519; % Stopband Attenuation
dens = 20; % Density Factor

% Calculate the order from the parameters using FIRPMORD.
[N, Fo, Ao, W] = firpmord([Fpass, Fstop]/(Fs/2), [1 0], [Dpass, Dstop]);

% Calculate the coefficients using the FIRPM function.
b = firpm(N, Fo, Ao, W, {dens});
Hd = dfilt.dffir(b);


now to check the functionality im passin noise sigal using following function

%noisy signal
y = wgn(10000,1,1);
Fs=2.677e6;

%%Analyze data time domain
T=1/Fs;
L=5;
t=(0:L-1)*T; %time vector

%analyze data freq domain
NFFT=L;
Y=fft(y,NFFT)/L;
f=Fs/2*linspace(0,1,NFFT/2+1);

%plot single sided amplitude spectrum
figure; plot(f,20.*log(abs(Y(1:NFFT/2+1))))

title('single sided amp of y(t)')
xlabel('freq(Hz)')
ylabel('|Y(f)|')

%change to fixed point data
y_fixed=fi(y,1,16,15);


after this i dont know how to see the output as attenuated wave.. pls help... urgent