anybody know the difference between filter and filtfilt

[mapi]

Hi,
I want to filter some experimental data: y=f(x),---smooth the y values. But I have tried both filter and filtfilt, what is the difference between them? Or which one is better?

Mapi

 

[SomptingGuy]

filtfilt() implements filter() twice. first forwards, then backwards. You get twice the attenuation and zero phase shift. So filtfilt() is probably what you want. I have a vague recollection that filtfilt() is only in the signal processing toolbox? If so it wouldn't take too many brain cells to implementy it by hand.

- Steve

 

[mapi]

Thanks. I will read the help file carefully again.

Mapi

 

[dumexx]

hello,

i also need some help regarding this filtfilt thingy..
the thing is.. i am supposed to check the phase response using both functions to see the differences. i just dunno where to start..

some of the lines that i have written..

b=[1];
a=[1, -0.8];
w=0:0.1:10;

x=sin(w);
y=filter (b,a,x);

figure(1);
subplot(2,1,1);
plot (w,x);
subplot(2,1,2);
plot(w,y);

[H]=freqz (b,a,w);
figure(2);
subplot(2,1,1);
plot(w,abs(H));
subplot(2,1,2);
plot(w,angle(H));

y1=filtfilt (b,a,x);
figure (3);
plot(w,y1);

[H1]=freqz (b,a,w);
figure (4);
subplot(2,1,1);
plot(w,abs(H1));
subplot(2,1,2);
plot(w,angle(H1));

it is obvious that both phase response are the same bcos they still use the same (b,a,w).. so what should i do?

and another question.. how can i obtain the phase shift of both y and y1 from the curve??

can i just read from the curve or is there any other function that i am not aware of??

thanks..

regards

newbie with matlab

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376

 

[SomptingGuy]

It must be. He has managed to enlist Rune in one of his identical postings on CSSM. But has made a complete hash of the advice given.

- Steve