Re: [Discuss-gnuradio] Basic IIR Filtering

[Matt Ettus]

> I am finding that if I use a tap vector length of greater than 4 the
> code stops working. Instead of a tone I get no noise.
>  
You may be getting instabilities, which is common with high order IIR 
filters.  However, Just to make sure the problem isn't the code, try 
making a 2 tap filter and instantiate it as a 4 tap, setting the other 
taps to 0 or 1 as appropriate. 

If you find that instability is the problem, you are better off breaking 
your filter into cascaded biquad sections.  Matlab should be able to do 
that for you.

Matt