[sdiy] HP from LP ?

[Sean Ellis]

I have seen a way to inject the signal into the ladder to get a highpass response, Tom Gamble was the first person I saw do this but I cant find the original message (was on SDIY sometime around 2000). I have gotten highpass from the 303 filter in the same way:

https://soundcloud.com/tensiontype/303-highpass1

At 3:35 the pop is switching back to low pass. Will have to pull out the synth to reverse engineer exactly what the change was, I added a pot to act as notch.

Actually while uploading I found this http://www5b.biglobe.ne.jp/%7Ehoushu/synth/Vcfv0212.GIF

[http://www5b.biglobe.ne.jp/%7Ehoushu/synth/Vcfv0212.GIF]




________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Tom Wiltshire <tom at electricdruid.net>
Sent: Tuesday, 1 August 2017 7:28 AM
To: Julian Schmidt
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] HP from LP ?

I’m getting the feeling here that just a simple subtraction of the lowpass response from the input isn’t enough (ahem). If you want better than -6dB/oct, you need to do some more sophisticated summing of the input and the various outputs, and you’d better make sure you’ve got accurate resistor values and signal levels too, since that provides a limit to how m such attenuation you can expect in the stop band off you high pass filter. How good is your signal cancellation? -40db? -60dB? Unlikely to be better than that.

That’s not to say that it’s not worth it.. As Paula said, the Xpander service manual is the original source, and Oliver Gillet’s documents on the Four Pole Mission board for the Shruthi expand on that:

https://mutable-instruments.net/archive/documents/pole_mixing.pdf

Basically, generating a multi-pole highpass from a multipole lowpass response isn't as simple as just taking one off the other. These are both great filters and worth doing.

HTH,
Tom


==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 31 Jul 2017, at 20:50, Julian Schmidt <elfenjunge at gmx.net> wrote:
>
> Have a look at this paper on page 64, Multimode Ladder Filter
> https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf
THE ART OF VA FILTER DESIGN - Native Instruments<https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_1.1.1.pdf>
www.native-instruments.com
Preface The classical way of presentation of the DSP theory is not very well suitable for the purposes of virtual analog lter design. The linearity and time-invariance


>
> You can mix the different poles with a simple opamp mixer.
> input -4 * Pole1 + 6 * Pole 2 -4 * Pole 3 + Pole 4 will yield a funky looking HP filter
>
> julian
>
>
> Am 31.07.2017 um 20:10 schrieb Michael Zacherl:
>> Hi,
>> I discussed that briefly in one of the last SDIY meetings,
>> did some experiments but never came to a sound conclusion:
>>
>> Is there a ‘cheap’ way of turning a low pass filter into a high pass?
>>
>> How’s that possibly approached?
>> Just something like subtracting the LP’s output from its input signal?
>> If so, what about resonance?
>>
>> My point about doing that cheaply is the (upcoming) release of two synths with Moog ladder filter featuring a switchable high pass mode.
>> To my knowledge, there was no resonating HP filter from Moog so far in any synth.
>> Until now.
>> Since both synths (Moog Mother-32 and Behringer Model D) are on the budget side in terms of money I’d rather expect a simple solution compared to a, say, DSI Pro-2 with two fully featured filters in it.
>>
>> Any hints?
>> Thanks, Michael.
>>
>>
>> --
>> http://mz.klingt.org
mz .-- mz --. mz<http://mz.klingt.org/>
mz.klingt.org
14 July 2016 – Radio Orange: "A Time Traveller's Guide to Early Electronic Music" on Katrins Klangschiene


>>
>>
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