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OnePole.h

/*
      dsp/OnePole.h
      
      Copyright 2003-4 Tim Goetze <tim@quitte.de>
      
      http://quitte.de/dsp/

      one pole (or one zero, or one zero, one pole) hi- and lo-pass filters.

*/
/*
      This program is free software; you can redistribute it and/or
      modify it under the terms of the GNU General Public License
      as published by the Free Software Foundation; either version 2
      of the License, or (at your option) any later version.

      This program is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      GNU General Public License for more details.

      You should have received a copy of the GNU General Public License
      along with this program; if not, write to the Free Software
      Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
      02111-1307, USA or point your web browser to http://www.gnu.org.
*/

#ifndef _ONE_POLE_H_
#define _ONE_POLE_H_

namespace DSP {
      
class OnePoleLP
{
      public:
            d_sample a0, b1, y1;

            OnePoleLP (double d = 1.)
                  {
                        set (d);
                        y1 = 0.;
                  }

            inline void reset()
                  {
                        y1 = 0.;
                  }

            inline void set_f (double fc)
                  {
                        set (exp (-2 * M_PI * fc));
                  }

            inline void set (double d)
                  {
                        a0 = (d_sample) d;
                        b1 = (d_sample) 1. - d;
                  }

            inline d_sample process (d_sample x)
                  {
                        return y1 = a0 * x + b1 * y1;
                  }
            
            inline void decay (double d)
                  {
                        a0 *= d;
                        b1 = 1. - a0;
                  }
};

class OnePoleHP
{
      public:
            d_sample a0, a1, b1, x1, y1;
            double fc;

            OnePoleHP (double d = 1.)
                  {
                        fc = 0;
                        set (d);
                        x1 = y1 = 0.;
                  }

            void set_f (double f)
                  {
                        fc = f;
                        set (exp (-2 * M_PI * fc));
                  }

            inline void set (double d)
                  {
                        a0 = (d_sample) ((1. + d) / 2.);
                        a1 = (d_sample) ((1. + d) / -2.);
                        b1 = d;
                  }

            inline d_sample process (d_sample x)
                  {
                        y1 = a0 * x + a1 * x1 + b1 * y1;
                        x1 = x;
                        return y1;
                  }

            void reset()
                  {
                        x1 = y1 = 0;
                  }
};

} /* namespace DSP */

#endif /* _ONE_POLE_H_ */

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