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/root/src/subsynth/syn/Util/Filter.h

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#ifndef SYN_BASIC_FILTERS_H
#define SYN_BASIC_FILTERS_H

namespace syn
{
   
class FirFilter
{
public:
   FirFilter()
   {
      mBuf[0] = 0.0f;
      mBuf[1] = 0.0f;
      mBuf[2] = 0.0f;
      mCoef[0] = 0.0f;
      mCoef[1] = 0.0f;
      mCoef[2] = 0.0f;
   }

   void filter( float& sample )
   {
      float temp;
      mBuf[2] = sample;
      temp = mCoef[0] * mBuf[2] + mCoef[1] * mBuf[1];// + mCoef[2] * mBuf[0];
      mBuf[0] = mBuf[1]; 
      mBuf[1] = mBuf[2];
      sample = temp;
   }

   int order() const { return 3; }

   void invert()
   {
      // invert all even coefs...
      mCoef[1] = 1.0f / mCoef[1];
      //mCoef[1] = -mCoef[1];
   }

   void setSimpleLowPass()
   {
      mCoef[0] = 0.5f;
      mCoef[1] = 0.5f;
      mCoef[2] = 0.0f;
   }

   void setSimpleHighPass()
   {
      mCoef[0] = 0.5f;
      mCoef[1] = -0.5f;
      mCoef[2] = 0.0f;
   }

   void setSimpleBandReject()
   {
      mCoef[0] = 0.5f;
      mCoef[1] = 0.0f;
      mCoef[2] = 0.5f;
   }

   void setSimpleBandPass()
   {
      mCoef[0] = 0.5f;
      mCoef[1] = 0.0f;
      mCoef[2] = -0.5f;
   }

   void setCutoff( float fc, float sampRate )
   {
      const int N = this->order();
 
      for (int k = 0; k < N; ++k)
      {
         float k_minus_n_over_2 = k - (N / 2.0f);
         float junk = 2.0f * Math::PI * k_minus_n_over_2;
         float top = Math::sin( junk * (fc / sampRate) );
         float bottom = Math::PI * k_minus_n_over_2;
         float left = top / bottom;
         float right = 0.54f + 0.46f * Math::cos( junk / N );
         mCoef[k] = left * right;
         //std::cout<<"coef::"<<mCoef[k]<<std::endl;
      }
   }

private:
   float mCoef[3]; // order 3 filter...
   float mBuf[3];  // keep a history of 3 samples...
};

class SimpleLowPass
{
public:
   SimpleLowPass() : mCutoff( 1.0f ), last( 0 )
   {
       this->setCutoff( mCutoff, 44100.0f );
   }

   void setCutoff( float cutoff, float sampRate )
   {
      mCutoff = cutoff / sampRate;
      if (mCutoff < 0.0f) mCutoff = 0.0f;
      if (mCutoff > 1.0f) mCutoff = 1.0f;
               
      a = 1.0f / ( 1.0f + 0.2756644477f / mCutoff );
      b = 1.0f - a;
   }

   inline void filter( float& data )
   {
      data = last = a*data + b*last;
   }
   
   float mCutoff, last;
   float a, b;
};

class SimpleHighPass
{
public:
   SimpleHighPass() : mCutoff( 1.0f ), lastin( 0 ), lastout( 0 )
   {
       this->setCutoff( mCutoff, 44100.0f );
   }

   void setCutoff( float cutoff, float sampRate )
   {
      mCutoff = cutoff / sampRate;
      if (mCutoff < 0.0f) mCutoff = 0.0f;
      if (mCutoff > 1.0f) mCutoff = 1.0f;

      a = 1.0f / ( 1.0f + 10.8827961853f * mCutoff );
   }

   inline void filter( float& data )
   {
      lastout = a*lastout + data - lastin;
      lastin = data;
      data = lastout;
   }
   
   float mCutoff, lastin, lastout;
   float a;
};

class SimpleLP
{
public:
   SimpleLP() : mCutoff( 44100.0f ), lastin( 0 ), lastout( 0 )
   {
      this->setCutoff( mCutoff, 44100.0f );
   }

   void setCutoff( float cutoff, float sampRate )
   {
      mCutoff = cutoff / sampRate;
      if (mCutoff < 0.0f) mCutoff = 0.0f;
      if (mCutoff > 1.0f) mCutoff = 1.0f;

      float omega = Math::aTan( Math::PI * mCutoff );
      a = -(1.0f - omega) / (1.0f + omega);
      b = (1.0f - b) / 2.0f;
   }

   void filter( float& data )
   {
      // dest[0] = b * (src[0] + src[-1]) - a * dest[-1]
      lastout = b * (data + lastin) - a * lastout;
      lastin = data;
      data = lastout;
   }

private:
   float mCutoff;
   float a, b;   // coefs
   float lastin, lastout; // sample history (data, lastin unfiltered, lastout filtered)
};

class RbjFilter
{
public:
   RbjFilter()
   {
   }

   void filter( float& sample )
   {
      // sample is current, 
      float temp;
      temp = (b0/a0)*sample + (b1/a0)*x[1] + (b2/a0)*x[0]
                            - (a1/a0)*y[1] - (a2/a0)*y[0];
      // keep a history...
      // oldest < 0, 1, sample|temp < newest
      x[0] = x[1];
      x[1] = sample;
      y[0] = y[1];
      y[1] = temp;
      
      // return the result...
      sample = temp;
   }


   float A;
   float omega;
   float sn;
   float cs;
   float alpha;
   float beta;
   void setup( float frequency, float sampRate, float dBgain = 20.0f, float Q = 1.0f )
   {
      A     = Math::sqrt( pow( 10.0f, (dBgain/20.0f) ) );
      //            = 10^(dBgain/40)    // (for for peaking and shelving EQ filters only)
      omega = 2.0f * Math::PI * frequency / sampRate;
      sn    = Math::sin( omega );
      cs    = Math::cos( omega );
      alpha = sn / (2.0f * Q);
      //            = sn*sinh[ ln(2)/2 * bandwidth * omega/sn ]     // (if bandwidth is specified instead of Q)
      //beta  = Math::sqrt[ (A^2 + 1)/S - (A-1)^2 ]   // (for shelving EQ filters only)
   }
      
         
   void setCutoff( float frequency, float sampRate )
   {
      setup( frequency, sampRate );

      //float s = (1.0f / Math::tan( omega / 2.0f )) * ((1.0f - 1.0f/z) / (1.0f + 1.0f/z));
      //Hs =   1.0f / (s * s + s / Q + 1.0f);
      a0 =   1.0f + alpha;
      a1 =  -2.0f * cs;
      a2 =   1.0f - alpha;
      b0 =  (1.0f - cs) / 2.0f;
      b1 =   1.0f - cs;
      b2 =  (1.0f - cs) / 2.0f;
   }

private:
   float mCoef[3];
   float x[3];
   float y[3];
   float Hs;
   float a0, a1, a2;
   float b0, b1, b2;
};

} // end namespace syn

#endif

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