[sdiy] HP from LP ?

[David G Dixon]

Yes, I should have clarified.  I use 2164 for all my filters, so my stages
are always inverting (because 2164 must terminate to virtual ground).


  _____  

From: Andrew Simper [mailto:andy at cytomic.com] 
Sent: Monday, July 31, 2017 6:37 PM
To: David G Dixon
Cc: Michael Zacherl; synth-diy mailing list
Subject: Re: [sdiy] HP from LP ?


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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