# [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 14:36:55 CEST 2013

```> This is the online tool:
http://kmt.hku.nl/~pieter/cgi-bin/resp/nph-PZT.cgi.

damn, it says it cant load it here :P

but this seems like a simple formula to try out, from what you copied here.
If that's all, and if I got what it means, I can see a patch coming right
now :) let's see!

thanks

2013/9/24 Funs Seelen <funsseelen at gmail.com>

> Hi Alexandre,
>
> This is the online tool:
> http://kmt.hku.nl/~pieter/cgi-bin/resp/nph-PZT.cgi.
>
> It starts with an example and every time you refresh the page it gives you
> a new one. If you scroll down there's a link that tells you how the
> coefficients were calculated, e.g.:
> 2 zeros give 3 coefficients: *a0* = G
> *a1* = -G(Z0 + Z1)
> *a2* = G(Z0*Z1)
>
> 2 poles give 3 coefficients: *b0* = 1
> *b1* = -(P0 + P1)
> *b2* = (P0*P1)
>
> The linear difference equation is derived from these as you can see.
>
> Regards,
> --Funs
>
>
> On Tue, Sep 24, 2013 at 7:36 AM, Alexandre Torres Porres <porres at gmail.com
> > wrote:
>
>> for what i see, it's not some sort of straight formula, right? seems a
>> bit more complicated than that.
>>
>> cheers
>>
>>
>> 2013/9/23 Funs Seelen <funsseelen at gmail.com>
>>
>>> On Mon, Sep 23, 2013 at 5:35 PM, Alexandre Torres Porres <
>>> porres at gmail.com> wrote:
>>>
>>>>
>>>> thanks, here's a pic of what I have so far
>>>>
>>>>
>>>> https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn1/11212_10151872996046683_1825736206_n.jpg
>>>>
>>>
>>> Cool.
>>>
>>>
>>>>
>>>> > For extra inspiration you could have a look at PoZeTools
>>>>
>>>> It sure does look like what I need. Thanks. But extracting what I need
>>>> to know about the math of converting from coordinates to coefficients was
>>>> just over my head :P unfortunately, sorry.
>>>>
>>>> I was hoping for something simpler, like just the operations needed. If
>>>> the info is in code, I need it to more explicit. I'd really appreciate if
>>>> anyone knows how to read from this and just points it out for me so I can
>>>> put it in a patch.
>>>>
>>>> I'm assuming it's rather simple math
>>>>
>>>
>>> I remember I once learned how to do this but never repeated the
>>> practice. If I find time to do that I would gladly try to figure it out
>>> again, but if someone more experienced feels the urge to chime in before
>>> that time I would be very happy too :).
>>>
>>
>>
>
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