rosic_BiquadFilter.h

#ifndef rosic_BiquadFilter_h
#define rosic_BiquadFilter_h

/**
This is an implementation of a simple one-pole filter unit.
*/

class BiquadFilter
{

public:

/** Enumeration of the available filter modes. */
enum modes
{
  BYPASS = 0,
  LOWPASS6,
  LOWPASS12,
  HIGHPASS6,
  HIGHPASS12,
  BANDPASS,
  BANDREJECT,
  PEAK,
  LOW_SHELF,
  //HIGH_SHELF,
  //ALLPASS,

  NUM_FILTER_MODES
};

//---------------------------------------------------------------------------------------------
// construction/destruction:

/** Constructor. */
BiquadFilter();   

//---------------------------------------------------------------------------------------------
// parameter settings:

/** Sets the sample-rate (in Hz) at which the filter runs. */
void setSampleRate(float newSampleRate);

/** Sets the filter mode as one of the values in enum modes. */
void setMode(int newMode);

/** Sets the center frequency in Hz. */
void setFrequency(float newFrequency);

/** Sets the boost/cut gain in dB. */
void setGain(float newGain);

/** Sets the bandwidth in octaves. */
void setBandwidth(float newBandwidth);

//---------------------------------------------------------------------------------------------
// inquiry

/** Sets the filter mode as one of the values in enum modes. */
int getMode() const { return mode; }

/** Returns the center frequency in Hz. */
float getFrequency() const { return frequency; }

/** Returns the boost/cut gain in dB. */
float getGain() const { return gain; }

/** Returns the bandwidth in octaves. */
float getBandwidth() const { return bandwidth; }

//---------------------------------------------------------------------------------------------
// audio processing:

/** Calculates a single filtered output-sample. */
inline float getSample(float in);

//---------------------------------------------------------------------------------------------
// others:

/** Resets the internal buffers (for the \f$ x[n-1], y[n-1] \f$-samples) to zero. */
void reset();

//=============================================================================================

protected:

// internal functions:
void calcCoeffs();  // calculates filter coefficients from filter parameters

float b0, b1, b2, a1, a2;
float x1, x2, y1, y2;

float frequency, gain, bandwidth;
float sampleRate;
int    mode;

};

//-----------------------------------------------------------------------------------------------
// inlined functions:

inline float BiquadFilter::getSample(float in)
{
// calculate the output sample:
float y = b0*in + b1*x1 + b2*x2 + a1*y1 + a2*y2 + TINY;

// update the buffer variables:
x2 = x1;
x1 = in;
y2 = y1;
y1 = y;

return y;
}


#endif // rosic_BiquadFilter_h