[sdiy] HP from LP ?

[paula at synth.net]

Michael,

  you can do it by simply inverting the input signal and adding the 
output of the lowpass to it.
  002 and the MonowaveII use a similar trick with the output from the 
first rung of the ladder filter, due to the phase you get a 'psuedo' 
bandpass. For inspiration, look at the oberheim xpander VCF schematics, 
mixing the outputs and the input will get you a whole bunch of filter 
shapes :)

Paula

On 2017-07-31 19:10, Michael Zacherl wrote:
> 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
> 
> 
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