filtering signal

Hi all,

I've been using the FDA-tool in matlab to design a bandpass filter. The frequency area of interest in my case is 2-7 Hz in a biological EEG signal. When I use my filter designed using the FDA-tool it seems to overdamp the signal in the beginning and in the end of the signal. In between it seems alright! I have tried to change my filter design, and to change my input signal, and I doesn't seem to change the overdamping effect. What to do???

My filter function looks like this:

function DataFiltBP = bandpass(dataW)
% M-File generated by MATLAB(R) 7.10 and the Signal Processing Toolbox 6.13. 
% Equiripple Bandpass filter designed using the FIRPM function.
% All frequency values are in Hz.
Fs = 200;  % Sampling Frequency
N      = 1000;  % Order
Fstop1 = 1.5;   % First Stopband Frequency
Fpass1 = 2;   % First Passband Frequency
Fpass2 = 7;   % Second Passband Frequency
Fstop2 = 7.5;   % Second Stopband Frequency
Wstop1 = 5;   % First Stopband Weight
Wpass  = 1;    % Passband Weight
Wstop2 = 5;   % Second Stopband Weight
dens   = 20;   % Density Factor

% Calculate the coefficients using the FIRPM function.
b  = firpm(N, [0 Fstop1 Fpass1 Fpass2 Fstop2 Fs/2]/(Fs/2), [0 0 1 1 0 ...
           0], [Wstop1 Wpass Wstop2], {dens});
Hd = dfilt.dffir(b);
DataFiltBP = filter(Hd,dataW);

You can try it out with any input signal, for example:

2*cos(5*pi*t)+sin(2*pi*t)

After using the filter try the following:

t=linspace(0,20,100000)
plot(t,DataFiltBP)

Thanks!

Answer 1

[altaf adil]

The problem is because of smooth transition of the filter. You can try increasing the density factor.