[sdiy] Oberheim Xpander VCF (newbie alert)

[David G. Dixon]

This talk of VCFs has led me to another newbie question:

What is the preferred method for implementing a cross-fade circuit?  I'm
assuming one channel's gain is increased from 0 to 1 while another's is
decreased from 1 to 0, and they both add up to one at any given setting?
How exactly is this done (it doesn't involve dual-gang pots, does it?  That
wouldn't be elegant at all!)?

>Original message:
Antti,

  you can indeed, and it doesn't have to be a "real" filter, it works  
with DSP filters too.
With the Monowave II and Phoenix apps I did for the Chameleon I did  
this.
take output after 1st pole, invert it... take output after fourth pole  
and cross fade between the two. In the middle you get a psuedo  
bandpass filter, but by doing the crossfade you can get a four pole  
filter with a bit more fizz and a bit less bottom.

   MonowaveII examples here -
http://www.vacoloco.net/synths/monowave2/sounds.shtml

  Just look for "pole sweep" or similar.

  I did the same in hardware for the Defender voice card, you can here  
the filter being controlled by the two LFOs on this page ;-
http://www.vacoloco.net/synths/defender/sounds.shtml

   It's a great way to obtain a very very flexible filter for very  
little extra work!

Paul

On 15 Jan 2009, at 15:10, Antti Huovilainen wrote:

> On Thu, 15 Jan 2009, George Hearn wrote:
>
>> I've been pointed in the direction of the Oberheim XPander VCF.  I  
>> think
>> it's quite incredible how 16 filter modes can come out of one  
>> filter.  Does
>> this not make it about the most versatile analogue filter design  
>> ever?
>
> You can get the same modes (and over a dozen more) from any 4 pole  
> cascaded RC style filter (Moog ladder, CEM, OTA etc).
>
> Antti
>
> "No boom today. Boom tomorrow. There's always a boom tomorrow"
>  -- Lt. Cmdr. Ivanova
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy