moogFF in freq gain reset

Moog VCF implementation, designed by Federico Fontana. A digital
implementation of the Moog VCF (filter).

     in - the input signal
   freq - the cutoff frequency
   gain - the filter resonance gain, between zero and 4
  reset - when greater than zero, this will reset the
          state of the digital filters at the beginning
          of a computational block.

The design of this filter is described in the conference paper
Fontana, F. (2007) Preserving the Digital Structure of the Moog
VCF. In Proc. ICMC07, Copenhagen, 25-31 August 2007

> import Sound.SC3

> do { n <- whiteNoise AR
>    ; let { y = mouseY KR 100 10000 Exponential 0.1
>          ; x = mouseX KR 0 4 Linear 0.1 }
>      in audition (out 0 (moogFF (n * 0.1) y x 0)) }

Note distortion at high gain.

> let { x = mouseX KR 100 20000 Exponential 0.1
>     ; y = mouseY KR 0.1 4.0 Linear 0.1
>     ; i = mix (saw AR (mce [0.99, 1, 1.01] * 440)) * 0.3 }
> in audition (out 0 (moogFF i x y 0))

> do { n <- lfNoise0 KR 0.43
>    ; let { p = pulse AR (mce [40, 121]) (mce [0.3, 0.7])
>          ; f0 = linLin n 0 1 0.001 2.2
>          ; f = linLin (sinOsc KR f0 0) (-1) 1 30 4200
>          ; y = mouseY KR 1 4 Linear 0.1 }
>      in audition (out 0 (moogFF p f (0.83 * y) 0)) }