[sdiy] What would be THE best, most versatile VCF available on DIY community ?

[Lanterman, Aaron]

On May 29, 2012, at 4:52 AM, Neil Johnson wrote:

>> The way it forms a two-pole filter with variable "Q" is to cascade two usual first-order LP filters (for instance) and then feed the output back to the input. I can't seem to find my notes on it now, but I remember working out the transfer function. Changing the feedback, IIRC, doesn't give you a Q (as typically defined for a 2nd-order filter) that varies independently of the "fc" (usually called the "cutoff"), as in the case of a State Variable Filter or a Sallen-Key. The fc also changes. So there's a subtle difference in how it responds.
> 
> Sounds more like a biquad arrangement - in your analysis did you notice if the bandwidth remained constant as Fc was changed?

You're right, if you changed the cutoffs of the cell Q changed too. (Again, this is IIRC - I wish I could find my notes...)

- Aaron