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

 From: Przemek Klosowski Subject: Re: Butter Command - Maximum Order and Cut Off Frequency - Issues Date: Fri, 19 Jan 2018 11:57:17 -0500 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

```On 01/18/2018 06:56 PM, Shadders wrote:
```
```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)
=================================
```
```There's an interesting numerical instability around 0.972:

```
for d=0.96+[.010:.0001:.015]; [b,a] = butter(12,d );     y = filter(b, a, x); plot(n(500:3600), y(500:3600)),title(d); d,pause(.5); end
```
I have no idea what is going on but it's kind of pretty :)

```