Re: HPF

Hi Jory,

The Biquad topology allows for a filter with two poles and two zeros. Each
pole gives a 6dB/octave slope. So with 2 poles, biquad can either get 6dB
or 12dB slope. To get more than 12dB, one can just cascade multiple Biquad
filters and the slopes add linearly. So 2 BiquadFilterNode in series will
give you 24dB etc. But you're indeed limited to multiples of 12dB/octave.

Another way could be to implement a single pole filter using a DelayNode
and feeding it back through a GainNode. I haven't experimented with that
yet, but will try it out sometime this week. I believe with a combination
of the BiquadFilterNode and a Single Pole filter we should be able to get a
filter with a slope of any power of 6dB/octave.

-Chinmay


On Mon, Apr 7, 2014 at 3:46 AM, Jory <me@jory.org> wrote:

> Hi,
>
> I need to implement a highpass filter with a 24 dB/octave slope, but
> the Biquad filter node only does 12 dB/oct. I would imagine this
> shouldn't be hard to do, and perhaps I have to do it with a
> ScriptProcessorNode, but I also wonder why the Biquad.highpass is fixed
> at 12 dB/oct, rather than allowing the user to select 6, 12, 18, or 24
> dB?
>
> Any help on how I can implement this would be greatly appreciated.
> Thanks!
>
> Jory K. Prum
> Sound Guy
>
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