# [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 15:35:46 CEST 2013

```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