use filtfilt with error of Not enough input arguments

Hi all: I used fdatool designed a bandpass filter 'bp521',to filter my signal 'SINGAL', the main contents of the filter are below:

function Hd = bp521
% All frequency values are in kHz.
Fs = 90;  % Sampling Frequency

Fstop1 = 3.5;               % First Stopband Frequency
Fpass1 = 5.5;             % First Passband Frequency
Fpass2 = 21;              % Second Passband Frequency
Fstop2 = 23;              % Second Stopband Frequency
Dstop1 = 0.001;           % First Stopband Attenuation
Dpass  = 0.057501127785;  % Passband Ripple
Dstop2 = 0.0001;          % Second Stopband Attenuation
flag   = 'scale';         % Sampling Flag

% Calculate the order from the parameters using KAISERORD.
[N,Wn,BETA,TYPE] = kaiserord([Fstop1 Fpass1 Fpass2 Fstop2]/(Fs/2), [0 ...
                             1 0], [Dstop1 Dpass Dstop2]);

% Calculate the coefficients using the FIR1 function.
b  = fir1(N, Wn, TYPE, kaiser(N+1, BETA), flag);
Hd = dfilt.dffir(b);

I can use filter(bp521,SIGNAL), but when I want to use it by filtfilt, it always gave error: 'Not enough input arguments.', so I wonder why?? could there anyone help me with this?

Thank you in advance!

[Star Strider]

Include your call to filtfilt in the code you post.

Answer 1

[Honglei Chen]

You can do the following:

bp521Coeff = coeffs(bp521);
filtfilt(bp521Coeff.Numerator,bp521Coeff.Denominator,SIGNAL)

[Miao]

Thank you very much for your help, I tried, the bp521Coeff is a 1*1 struct, but there are nothing in bp521Coeff.Denominator?

[Honglei Chen]

oh, it's an FIR, so you just do

filtfilt(bp521Coeff.Numerator,1,SIGNAL)