Difference between bode and freqz
I create a filter in MATLAB like this:
[num,den] = ellip(10,0.1,50,4000/22050,'high');
Using freqz , I found the frequency response of the filter as follows:
freqz(num,den)
This gives the expected high pass filter graph. However, if I try to plot the same set of values using the bode function , I get something completely different.
bode(tr(num,den))
This creates a graph of the low pass filter. Can't I understand how these functions work? I believe freqz used transfer function coefficients as arguments. This is also what I do with the bode function.
Why the difference?
source to share
[b,a] = ellip(n,Rp,Rs,Wp)
where b,a
are representatives of the z-area,
and tf
by default - for s-domain:
you can use filt
instead,
[b,a] = ellip(10,0.1,50,4000/22050,'high');
freqz(b,a)
figure
bode(filt(b,a))
You can also use bode(tf(b,a,-1,'variable','z^-1'))
.
Check variable property
on tf
.
A string that defines the display variable of the transfer function. The variable can take the following values:
's' - Default for continuous time models
'z' - Default value for discrete time models
'p' is equivalent to 's'
'q' - equivalent to 'z'
'z ^ -1' - Reverse value of 'z'
'q ^ -1' - Equivalent to 'z ^ -1'
source to share