Band pass filter problem(filtfilt)

[Anton igfne]

Hey!
I got a problem while designing a band pass filter,
I want to use filtfilt and then plot it, I know I have to have a input which is at least 3 times the filter order. Even if I have set a input which lives up to that requirement I get the following error massage.
"Error using filtfilt (line 78)
Not enough input arguments."

when using filt there is no problem.

(Yes I do know I use a Fs lower than design when plotting, I do that due to limit of computational force on the PC)


%function Hd = TestX1
%TESTX1 Returns a discrete-time filter object.

% MATLAB Code
% Generated by MATLAB(R) 8.5 and the DSP System Toolbox 9.0.
% Generated on: 02-Apr-2015 13:59:31

% Equiripple Bandpass filter designed using the FIRPM function.

% All frequency values are in MHz.
Fs = 20; % Sampling Frequency

Fstop1 = 4.8; % First Stopband Frequency
%4.8e6*(1/20000000)*2*pi=0.48pi normalised
Fpass1 = 4.9; % First Passband Frequency
Fpass2 = 5.1; % Second Passband Frequency
Fstop2 = 5.2; % Second Stopband Frequency
Dstop1 = 0.001; % First Stopband Attenuation
Dpass = 0.00057564620966; % Passband Ripple
Dstop2 = 0.001; % Second Stopband Attenuation
dens = 20; % Density Factor

% Calculate the order from the parameters using FIRPMORD.
[N, Fo, Ao, W] = firpmord([Fstop1 Fpass1 Fpass2 Fstop2]/(Fs/2), [0 1 ...
0], [Dstop1 Dpass Dstop2]);

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


%%

rng default
length=10;
Fs = 2000;
Samples=Fs*length;
Fcenter=Fs/4;
t = linspace(0,length,Samples);
x = cos(2*pi*Fcenter*t);%+0.5*randn(size(t));
%x=[x,zeros(length(x)*2)];
y = filter(Hd,x);

plot(t(1:Samples),x(1:Samples))
hold on
plot(t(1:Samples),y(1:Samples))

yzp = filtfilt(Hd,x);
plot(t(length.yzp),yzp)
xlabel('Time (s)')
ylabel('Amplitude')
legend('Original Signal','Filtered Data')
% [EOF]