[sdiy] tanh() and approximations and warping, why is my maths wrong?

[Andrew Simper]

Which digital filter model is being used that needs pre-warping of the
cutoff parameter?

Andy

On Tue, 11 Jun 2019 at 04:58, Gordonjcp <gordonjcp at gjcp.net> wrote:

> On Mon, Jun 10, 2019 at 09:11:58PM +0100, Tom Wiltshire wrote:
> > I think what he’s looking for is to know why x/(1+x) gives the right
> warping to get the correct cutoff frequency.
> >
> > Since I know very little of how digital filter models are derived from
> their analog counterparts and the approximations inherent in that process,
> I’m not the person to ask…
> >
> > Tom
>
> That's it exactly.  I'm not great at maths and the kind of algebra that
> goes into this sort of thing is a bit much for me, but x/(1+x) gets the
> filter tracking absolutely bang on.
>
> --
> Gordonjcp
>
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