Filter Design Basics

Hello.

I have a simple filter H(z) = 1 - z^-1

I can see my filter by writing:

b = [1 -1];
freqz(b,1);

what I would like to know is how to get this into the format for the filter design toolbox.

eg

d=fdesign.lowpass('N,Fc',80,0.5);
Hd=design(d);
freqz(Hd);

In my case, what would i be passing to fdesign.m, or design.m.

I know they should give the same answer, but with a different plot.

Or is it not possible to get the plotyy output if you know your filter coefficents?

thank you!!

Answer 1

[Wayne King]

Are you saying you already know the filter coefficients? In

H(z) = 1-z^{-1}

you have a high pass filter and you can create a filter object like design() would produce with:

     Hd = dfilt.df1([1 -1],1);
     fvtool(Hd);

If you do not already have the filter coefficients, then you can design the filter with fdesign and design and obtain the coefficients.

[Matlab2010]

Yes I already have the coefficents.

The above is great. thank you.

One question -- the output does not give me a phase response? Can I get it to?

[Wayne King]

Yes, you can do:

[phi,w] = phasez(Hd);

% or

b = [1 -1];

[phi,w] = phasez(b,1);