# [PD] from poles/zeros to biquad coefficients - how to? (something like max's z-plane)

Alexandre Torres Porres porres at gmail.com
Tue Sep 24 15:38:16 CEST 2013

```hey, starting to see what you mean much more clear, cool, really excited.
Thanks a lot!!!!!

2013/9/24 Alexandre Torres Porres <porres at gmail.com>

> so you're basically saying all i need to use is use only the real part,
> right?
>
> my frankenstein was working and alive for several times until i tried some
> bandpass coeff, let's se if i fix this now :)
>
>
> 2013/9/24 Funs Seelen <funsseelen at gmail.com>
>
>>
>>
>>
>> On Tue, Sep 24, 2013 at 3:08 PM, Funs Seelen <funsseelen at gmail.com>wrote:
>>
>>> On Tue, Sep 24, 2013 at 2:50 PM, Alexandre Torres Porres <
>>> porres at gmail.com> wrote:
>>>
>>>> one doubt emerges really soon anyway. Since they are complex (there are
>>>> two coordinate numbers for each pole and zero) how do I get only one number
>>>> by, for example, summing or multiplying one pole to the other? as in:
>>>>
>>>> *b1* = -(P0 + P1)
>>>> *b2* = (P0*P1)
>>>>
>>>
>>> You don't, the coefficients can be complex too. However, I discovered
>>> that mirroring (*) every pole and zero results in just real values without
>>> imaginary part. I don't have any mathematical proof for this, but it
>>> probably wouldn't be too hard to find such.
>>>
>>
>> I remembered again, it's called the complex conjugate.
>> http://en.wikipedia.org/wiki/Complex_conjugate
>>
>>
>>
>>>
>>> *) adding another pole/zero for each complex one, like z=-j if you