Distortion (algorithm 3)
------------------------

Similar to Distortion (algorithm 1) but uses Hi & Low Pass Filters from
Filters. Algorithm is HPF -> Distortion -> LPF. There are parameters for
Hi & Low Pass Filters : hipassfreq & lowpassfreq is the cutoff frequencies,
and the hipassQ & lowpassQ in the EE kinda definition for bandwidth. The
larger the Q, the wider the band, and vice versa. The drive controls the
amount of overdrive. The volume to balance the effect volume with the
bypassed level. The dry_mix is the volume of input signal & the wet_mix is
the volume of distorted signal. The feedback sets feedback of distortion.

Controls:

    drive       - distortion drive
                  (0<= <=5)
    dry_mix     - dry (unaffected) signal mix
                  (-5<= <=5)
    wet_mix     - wet (affected) signal mix
                  (-5<= <=5)
    feedback    - feedback
                  (-1<= <=1)
    volume      - distortion volume
                  (0=< <=2)
    hipassfreq  - cutoff frequency for hi pass filter
                  (0< <RATE/2)
    hipassQ     - the EE kinda definition for hi pass filter
                  (0< <=1)
    lowpassfreq - cutoff frequency for low pass filter
                  (0< <RATE/2)
    lowpassQ    - the EE kinda definition for low pass filter
                  (0< <=1)

Work formula implemented in this distortion algorithm is
out[i] = in[i] * dry + sign(in[i] - in[i-1]) * exp(abs(in[i]) * drive) * wet.
See. Its do next wave:
    Normal Sin Wave              Wave distorted by algorithm
                                     *
                                    * *
    ****                            * *
   *    *                           * *  *
  *      *                         *  * * *
 *        *                       *   * *  *
*          *                     *    * *   *
*          *                     *     *    *
------------*-------------       ------------*-------------
             *          *                     *     *    *
             *          *                     *    * *   *
              *        *                       *   * *  *
               *      *                         *  * * *
                *    *                           * *  *
                 ****                            * *
                                                 * *
                                                  *