[PD-dev] ggee: equalizer - bug?

[guenter geiger]

Hi Ben,

Yes, you are absolutely right ! Wondering how this could happen ...
The version in CVS is fixed now. Thanks a lot for tracking this down.

Greetings,

Guenter

On Tue, 26 Nov 2002, Ben Saylor wrote:
> Hi Guenter + all,
>
> I was trying to build a graphic EQ using a chain of RBJ peaking filters
> (inspired by a message on music-dsp) and noticed that ggee's equalizer
> object doesn't seem to generate the right coefficients.  I'm guessing
> it's supposed to be the peakingEQ from
> http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt.
> The code in question is (ggee/filters/equalizer.c)
>
> 	t_float b0 = 1 + alpha*e_A(x->x_gain);
> 	t_float b1 = -2.*cos(omega);
> 	t_float b2 = 1;
> 	t_float a0 = 1 + alpha;
> 	t_float a1 = -2.*cos(omega);
> 	t_float a2 = 1 - alpha;
>
> but I think it should be
>
> 	t_float b0 = 1 + alpha * e_A(x->x_gain);
> 	t_float b1 = -2. * cos(omega);
> 	t_float b2 = 1 - alpha * e_A(x->x_gain);
> 	t_float a0 = 1 + alpha / e_A(x->x_gain);
> 	t_float a1 = -2. * cos(omega);
> 	t_float a2 = 1 - alpha / e_A(x->x_gain);
>
> After changing these lines, it behaves as expected (as a peaking filter,
> while before it was a funny-shaped peak with a notch beside it).
>
> Ben
>
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