[sdiy] Oberheim Xpander VCF

[Tom Wiltshire]

Yes, it is more advanced, but it is also more complicated.

Having four LPF stages and a mixer is pretty straightforward, but  
having four stages that are switchable between LPF, HPF and APF is  
quite a bit more involved and also removes the possibility of  
morphing between responses.

WRT Tim's point about the Doepfer filter, I'm not at all surprised  
that many of the filter settings in the A107 don't sound that  
different - with that many (36), I'd have thought they're going to,  
no? Perhaps it only needs 8 or 10 presets, or maybe 15 like the  
Xpander is enough - the point is that that is already many times more  
flexibility than your average analogue filter (24db lowpass  
or...errrr...well, 12dB lowpass if you're lucky). There are only a  
few synths (some, but not many) that go beyond this.

Still, I think this is a fertile area for experimentation, in both  
the digital and analogue domains. We should all get designing all  
kinds of interesting multimode filters!

T.


On 15 Jan 2009, at 20:27, Scott Nordlund wrote:

>
> Actually, this is more advanced and takes a quite different  
> approach to simply mixing the individual filter stages.  The  
> flexibility here is impressive!  I wonder though how useful some of  
> the configurations would be, though...
>
> It could easily be built from OTAs as well...
>
>
> ----------------------------------------
>> Date: Thu, 15 Jan 2009 12:01:34 -0800
>> To: synth-diy at dropmix.xs4all.nl
>> From: jason at redfish.net
>> Subject: RE: [sdiy] Oberheim Xpander VCF
>>
>> btw Craig Anderton did something similar with the Multiple  
>> Identity Filter --
>>
>> http://www.crowncity.net/ratcave/Electro/MIF/mif.html
>>
>> i have a spare 3320 and i've been meaning to put this together,  
>> but...
>>
>>> Folks,
>>>
>>> How about using digital pots for adjusting the mixer and setting the
>>> Q/gain of the filter? Then you can have a library of settings to
>>> select from.
>>>
>>> Fascinating thread.
>>>
>>> --TimR
>>
>>
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