[sdiy] HP from LP ?

Jacob Watters jacobwatters at gmail.com
Tue Aug 1 06:03:11 CEST 2017

This thread made me experiment a bit with a Roland based filter that I have
been working on. I have a switch that inverts the output. This allows me to
mix the inverted version with the input signal, and create a highpass
filter type sound. It isn't a very good filter though - maybe because it is
only 6dB like people have mentioned. It sounds a bit weird too. My
experiments with a SVF sounded much better. However, it is a cool patching

-Jacob Watters

On Mon, Jul 31, 2017 at 9:36 PM, Andrew Simper <andy at cytomic.com> wrote:

> 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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