suggestions for highpass filter design in Matlab

Hello,

I want to implement a digital highpass filter in Matlab which should do the same job as simple analog filter(a RC filter) having a cutoff frequency of 0.5Hz ans sampling frequency needed is 500Hz. I got the similar in this thread

d = fdesign.highpass('Fst,Fp,Ast,Ap',0.5,0.6,40,1,500);
 Hd = design(d,'butter');

Is this the correct of way of implementation or does it need any changes I mean if the need is to implement a digital filter that can act similar to the analog filter.

Thanks.

Answer 1

[Wayne King]

Yes, that looks fine as long as you realize that you have essentially an allpass filter since you are such a low stopband frequency

d = fdesign.highpass('Fst,Fp,Ast,Ap',0.5,0.6,40,1,500);
Hd = design(d,'butter');
fvtool(Hd)

You can also use butter() to design the filter in the analog domain directly in radians/second.

   N = 30;
   [B,A] = butter(N,pi,'high','s');

[Stefan]

Wayne, When I tried to implement the above filter in fdatool,a warning message as appeared as shown below

Can you help me to figure out the problem. Thanks.