[sdiy] HP from LP ?

[Andrew Simper]

On 1 August 2017 at 08:29, David G Dixon <dixon at mail.ubc.ca> wrote:

> As others have said, it depends on the filter.
>
> For a four-pole cascaded-stage filter, you can get four different highpass
> modes by summing the filter stage outputs and the feedback + input in
> various gain ratios.  If the gain ratios are given for the {Feedback+Input,
> Stage 1 Output, Stage 2 Output, Stage 3 Output, Stage 4 Output}, then:
>
>  6dB HP: {1,1,0,0,0}
>
> 12dB HP: {1,2,1,0,0}
>
> 18dB HP: {1,3,3,1,0}
>
> 24dB HP: {1,4,6,4,1}
>
>
A quick point to the uninitiated: This only works if each of the cascaded
stages is inverting, otherwise you will need to flip the sign of every odd
or even weight.

Cheers,

Andy
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