typedef struct
{
  // Filter #1 (Low band)
  double  lf;       // Frequency
  double  f1p0;     // Poles ...
  double  f1p1;    
  double  f1p2;
  double  f1p3;

  // Filter #2 (High band)
  double  hf;       // Frequency
  double  f2p0;     // Poles ...
  double  f2p1;
  double  f2p2;
  double  f2p3;

  // Sample history buffer
  double  sdm1;     // Sample data minus 1
  double  sdm2;     //                   2
  double  sdm3;     //                   3

  // Gain Controls
  double  lg;       // low  gain
  double  mg;       // mid  gain
  double  hg;       // high gain
  
} EQSTATE;  

// Exports 
extern void   init_3band_state(EQSTATE* es, int lowfreq, int highfreq, int mixfreq);
extern double do_3band(EQSTATE* es, double sample);