Re: Butter Command - Maximum Order and Cut Off Frequency - Issues

[Shadders]

Hi,
No error messages, but the plots have bad values. 

The following works :

[b,a] = butter(12, 0.95) - plots are ok (multiple sine waves, different
frequencies, distinct)

The following plots a single exponentially increasing sine wave which
increases to values from 3e305 to -3e305, and terminates plotting at approx
1/8 of the expected values for the x axis :

[b,a] = butter(12, 0.98)

The output of the filter has from the 1/8 distance, NaN in the remainder of
the vector. 

Code that replicates failure - simple
=================================
nc = 5;   % Number of cycles of the waveform
fs = 192000;
ts = 1/fs;
n = 0:192000;               % Variable used for indexing
x = zeros(1, length(n));  % Input signal initialisation
[b,a] = butter(12, 0.98);        % Create the butterworth response
k1 = fs/1000;
k1n=0:(nc*k1); 
x1k = sin(2*pi*k1n/k1); 
x(1, 1000:1000+length(x1k)-1) = x1k;
y = filter(b, a, x);            % Use the filter function
figure(1);
plot(n, y)
=================================

Regards,
Shadders.



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