Doepfer

--- Dieter Doepfer <hardware@doepfer.de> wrote:

> From: "Dieter Doepfer" <hardware@doepfer.de>
> To: "Bakis Sirros" <synth_freak_2000@yahoo.com>
> Subject: MS20 high pass 6 or 12 dB ?
> Date: Mon, 6 Sep 2004 20:19:59 +0200
> 
> Dear members,
> 
> during the investigation for the planned A-106 MS20
> filter we discovered
> that - in our opinion - the MS20 highpass has 6dB
> slope only (in contrast to
> the lowpass which has indeed 12dB). In the original
> Korg specifications and
> MS20 manual nothing is said concering the filter
> slope but in all secondary
> publications we found only 12dB for the high pass
> but never 6dB. It seems
> that the writers copied from each other. But I'm
> still a bit careful as I
> cannot believe that nobody discovered during the
> last 25 years that the MS20
> highpass is 6dB only. Maybe we missed something.
> 
> But I don't believe that we made a mistake as both
> the measurements of the
> "real hardware" and the simulations generated the
> same results. We
> discovered this special quality as it was not
> possible to obtain a perfect
> bandpass and notch from the MS20 circuit (I do not
> speak about the usage of
> a separate filter for highpass and bandpass but
> about using the circuit as a
> kind of multimode filter with different inputs).
> There is always a phase
> shift of ~ 90 degrees between the HP and LP signal
> and consequently there is
> feedthrough for high and low frequencies of the
> bandpass resp. no notch with
> zero level at the center frequency. For full
> attenuation 180 degrees of
> phase shift woul be necessary - as for other
> filters.
> 
> Finally it is not important if the highpass slope is
> 6 or 12dB - provided
> that the sound is OK. But we want to be sure that we
> did not overlook
> something.
> 
> If anybody has details concerning 6/12dB highpass
> please let us know.
> 
> Thank you
> Dieter Doepfer
> 
> 


=====
Bakis Siros
Parallel Worlds / Polariton
Athens-Greece
[Doepfer_a100] group owner
http://www.shimarecords.co.uk
http://www.ward12.com


		
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