[PD] biquad~ with elementary filters [was: Re: dinosaurs ...]

[Charles Henry]

On Sun, Sep 21, 2008 at 8:56 AM, Claude Heiland-Allen
<claudiusmaximus at goto10.org> wrote:
> Damian Stewart wrote:
>>
>> Charles Henry wrote:
>>
>>> There is no zero at z=0.  I'm not sure about this one--but it seems as
>>> though it's impossible to have a zero at z=0?
>
> a zero at z=0 is a delay of 1 sample, so in:
>
> y = a x(0) + b x(-1) + c x(-2) + d y(-1) + e y(-2)
>
> there is a zero at z=0 if a == 0,
>  and two zeros at z=0 if a == 0 and b == 0
>
> (iirc)

z^-1 is the unit delay operator....
so,
Y(z)=z*X(z) means y(n) = x(n+1)

while this is not impossible... it's non-causal.  For real-time
filtering, you can't already know the sample that comes next.
I've been thinking about it for a little while now.  I hope we can figure it out

Chuck