STK biquad (two-pole, two-zero) filter class. More...

#include <BiQuad.h>

Inheritance diagram for stk::BiQuad:

Public Member Functions
	BiQuad ()
	Default constructor creates a second-order pass-through filter.

	~BiQuad ()
	Class destructor.

void	ignoreSampleRateChange (bool ignore=true)
	A function to enable/disable the automatic updating of class data when the STK sample rate changes.

void	setCoefficients (StkFloat b0, StkFloat b1, StkFloat b2, StkFloat a1, StkFloat a2, bool clearState=false)
	Set all filter coefficients.

void	setB0 (StkFloat b0)
	Set the b[0] coefficient value.

void	setB1 (StkFloat b1)
	Set the b[1] coefficient value.

void	setB2 (StkFloat b2)
	Set the b[2] coefficient value.

void	setA1 (StkFloat a1)
	Set the a[1] coefficient value.

void	setA2 (StkFloat a2)
	Set the a[2] coefficient value.

void	setResonance (StkFloat frequency, StkFloat radius, bool normalize=false)
	Sets the filter coefficients for a resonance at frequency (in Hz).

void	setNotch (StkFloat frequency, StkFloat radius)
	Set the filter coefficients for a notch at frequency (in Hz).

void	setLowPass (StkFloat fc, StkFloat Q=RECIP_SQRT_2)
	Set the filter coefficients for a low-pass with cutoff frequency fc (in Hz) and Q-factor Q.

void	setHighPass (StkFloat fc, StkFloat Q=RECIP_SQRT_2)
	Set the filter coefficients for a high-pass with cutoff frequency fc (in Hz) and Q-factor Q.

void	setBandPass (StkFloat fc, StkFloat Q)
	Set the filter coefficients for a band-pass centered at fc (in Hz) with Q-factor Q.

void	setBandReject (StkFloat fc, StkFloat Q)
	Set the filter coefficients for a band-reject centered at fc (in Hz) with Q-factor Q.

void	setAllPass (StkFloat fc, StkFloat Q)
	Set the filter coefficients for an all-pass centered at fc (in Hz) with Q-factor Q.

void	setEqualGainZeroes (void)
	Sets the filter zeroes for equal resonance gain.

StkFloat	lastOut (void) const
	Return the last computed output value.

StkFloat	tick (StkFloat input)
	Input one sample to the filter and return a reference to one output.

StkFrames &	tick (StkFrames &frames, unsigned int channel=0)
	Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.

StkFrames &	tick (StkFrames &iFrames, StkFrames &oFrames, unsigned int iChannel=0, unsigned int oChannel=0)
	Take a channel of the `iFrames` object as inputs to the filter and write outputs to the `oFrames` object.

Public Member Functions inherited from stk::Filter
	Filter (void)
	Class constructor.

unsigned int	channelsIn (void) const
	Return the number of input channels for the class.

unsigned int	channelsOut (void) const
	Return the number of output channels for the class.

virtual void	clear (void)
	Clears all internal states of the filter.

void	setGain (StkFloat gain)
	Set the filter gain.

StkFloat	getGain (void) const
	Return the current filter gain.

StkFloat	phaseDelay (StkFloat frequency)
	Return the filter phase delay at the specified frequency.

const StkFrames &	lastFrame (void) const
	Return an StkFrames reference to the last output sample frame.

virtual StkFrames &	tick (StkFrames &frames, unsigned int channel=0)=0
	Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.

Public Member Functions inherited from stk::Stk
void	ignoreSampleRateChange (bool ignore=true)
	A function to enable/disable the automatic updating of class data when the STK sample rate changes.

Additional Inherited Members
Static Public Member Functions inherited from stk::Stk
static StkFloat	sampleRate (void)
	Static method that returns the current STK sample rate.

static void	setSampleRate (StkFloat rate)
	Static method that sets the STK sample rate.

static void	clear_alertList ()
	Static method that frees memory from alertList_.

static std::string	rawwavePath (void)
	Static method that returns the current rawwave path.

static void	setRawwavePath (std::string path)
	Static method that sets the STK rawwave path.

static void	swap16 (unsigned char *ptr)
	Static method that byte-swaps a 16-bit data type.

static void	swap32 (unsigned char *ptr)
	Static method that byte-swaps a 32-bit data type.

static void	swap64 (unsigned char *ptr)
	Static method that byte-swaps a 64-bit data type.

static void	sleep (unsigned long milliseconds)
	Static cross-platform method to sleep for a number of milliseconds.

static bool	inRange (StkFloat value, StkFloat min, StkFloat max)
	Static method to check whether a value is within a specified range.

static void	handleError (const char *message, StkError::Type type)
	Static function for error reporting and handling using c-strings.

static void	handleError (std::string message, StkError::Type type)
	Static function for error reporting and handling using c++ strings.

static void	showWarnings (bool status)
	Toggle display of WARNING and STATUS messages.

static void	printErrors (bool status)
	Toggle display of error messages before throwing exceptions.

Static Public Attributes inherited from stk::Stk
static const StkFormat	STK_SINT8

static const StkFormat	STK_SINT16

static const StkFormat	STK_SINT24

static const StkFormat	STK_SINT32

static const StkFormat	STK_FLOAT32

static const StkFormat	STK_FLOAT64

Protected Member Functions inherited from stk::Stk
	Stk (void)
	Default constructor.

virtual	~Stk (void)
	Class destructor.

virtual void	sampleRateChanged (StkFloat newRate, StkFloat oldRate)
	This function should be implemented in subclasses that depend on the sample rate.

void	addSampleRateAlert (Stk *ptr)
	Add class pointer to list for sample rate change notification.

void	removeSampleRateAlert (Stk *ptr)
	Remove class pointer from list for sample rate change notification.

void	handleError (StkError::Type type) const
	Internal function for error reporting that assumes message in `oStream_` variable.

Detailed Description

STK biquad (two-pole, two-zero) filter class.

This class implements a two-pole, two-zero digital filter. Methods are provided for creating a resonance or notch in the frequency response while maintaining a constant filter gain.

Formulae used calculate coefficients for lowpass, highpass, bandpass, bandreject and allpass are found on pg. 55 of Udo Zölzer's "DAFX - Digital Audio Effects" (2011 2nd ed).

by Perry R. Cook and Gary P. Scavone, 1995–2023.

Member Function Documentation

◆ setResonance()

void stk::BiQuad::setResonance	(	StkFloat	frequency,
		StkFloat	radius,
		bool	normalize = `false`
	)

Sets the filter coefficients for a resonance at frequency (in Hz).

This method determines the filter coefficients corresponding to two complex-conjugate poles with the given frequency (in Hz) and radius from the z-plane origin. If normalize is true, the filter zeros are placed at z = 1, z = -1, and the coefficients are then normalized to produce a constant unity peak gain (independent of the filter gain parameter). The resulting filter frequency response has a resonance at the given frequency. The closer the poles are to the unit-circle (radius close to one), the narrower the resulting resonance width. An unstable filter will result for radius >= 1.0. The frequency value should be between zero and half the sample rate.

◆ setNotch()

void stk::BiQuad::setNotch	(	StkFloat	frequency,
		StkFloat	radius
	)

Set the filter coefficients for a notch at frequency (in Hz).

This method determines the filter coefficients corresponding to two complex-conjugate zeros with the given frequency (in Hz) and radius from the z-plane origin. No filter normalization is attempted. The frequency value should be between zero and half the sample rate. The radius value should be positive.

◆ setLowPass()

void stk::BiQuad::setLowPass	(	StkFloat	fc,
		StkFloat	Q = `RECIP_SQRT_2`
	)

Set the filter coefficients for a low-pass with cutoff frequency fc (in Hz) and Q-factor Q.

This method determines the filter coefficients corresponding to a low-pass filter with cutoff placed at fc, where sloping behaviour and resonance are determined by Q. The default value for Q is 1/sqrt(2), resulting in a gradual attenuation of frequencies higher than fc without added resonance. Values greater than this will more aggressively attenuate frequencies above fc while also adding a resonance at fc. Values less than this will result in a more gradual attenuation of frequencies above fc, but will also attenuate frequencies below fc as well. Both fc and Q must be positive.

◆ setHighPass()

void stk::BiQuad::setHighPass	(	StkFloat	fc,
		StkFloat	Q = `RECIP_SQRT_2`
	)

Set the filter coefficients for a high-pass with cutoff frequency fc (in Hz) and Q-factor Q.

This method determines the filter coefficients corresponding to a high-pass filter with cutoff placed at fc, where sloping behaviour and resonance are determined by Q. The default value for Q is 1/sqrt(2), resulting in a gradual attenuation of frequencies lower than fc without added resonance. Values greater than this will more aggressively attenuate frequencies below fc while also adding a resonance at fc. Values less than this will result in a more gradual attenuation of frequencies below fc, but will also attenuate frequencies above fc as well. Both fc and Q must be positive.

◆ setBandPass()

void stk::BiQuad::setBandPass	(	StkFloat	fc,
		StkFloat	Q
	)

Set the filter coefficients for a band-pass centered at fc (in Hz) with Q-factor Q.

This method determines the filter coefficients corresponding to a band-pass filter with pass-band centered at fc, where band width and slope a determined by Q. Values for Q that are less than 1.0 will attenuate frequencies above and below fc more gradually, resulting in a convex slope and a wider band. Values for Q greater than 1.0 will attenuate frequencies above and below fc more aggressively, resulting in a concave slope and a narrower band. Both fc and Q must be positive.

◆ setBandReject()

void stk::BiQuad::setBandReject	(	StkFloat	fc,
		StkFloat	Q
	)

Set the filter coefficients for a band-reject centered at fc (in Hz) with Q-factor Q.

This method determines the filter coefficients corresponding to a band-reject filter with stop-band centered at fc, where band width and slope are determined by Q. Values for Q that are less than 1.0 will yield a wider band with greater attenuation of fc. Values for Q greater than 1.0 will yield a narrower band with less attenuation of fc. Both fc and Q must be positive.

◆ setAllPass()

void stk::BiQuad::setAllPass	(	StkFloat	fc,
		StkFloat	Q
	)

Set the filter coefficients for an all-pass centered at fc (in Hz) with Q-factor Q.

This method determines the filter coefficients corresponding to an all-pass filter whose phase response crosses -pi radians at fc. High values for Q will result in a more instantaenous shift in phase response at fc. Lower values will result in a more gradual shift in phase response around fc. Both fc and Q must be positive.

◆ setEqualGainZeroes()

void stk::BiQuad::setEqualGainZeroes ( void )

Sets the filter zeroes for equal resonance gain.

When using the filter as a resonator, zeroes places at z = 1, z = -1 will result in a constant gain at resonance of 1 / (1 - R), where R is the pole radius setting.

◆ tick() [1/2]

StkFrames & stk::BiQuad::tick	(	StkFrames &	frames,
		unsigned int	channel = `0`
	)

inlinevirtual

Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.

The StkFrames argument reference is returned. The channel argument must be less than the number of channels in the StkFrames argument (the first channel is specified by 0). However, range checking is only performed if STK_DEBUG is defined during compilation, in which case an out-of-range value will trigger an StkError exception.

Implements stk::Filter.

{
#if defined(_STK_DEBUG_)
  if ( channel >= frames.channels() ) {
    oStream_ << "BiQuad::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif
 
  StkFloat *samples = &frames[channel];
  unsigned int hop = frames.channels();
  for ( unsigned int i=0; i<frames.frames(); i++, samples += hop ) {
    inputs_[0] = gain_ * *samples;
    *samples = b_[0] * inputs_[0] + b_[1] * inputs_[1] + b_[2] * inputs_[2];
    *samples -= a_[2] * outputs_[2] + a_[1] * outputs_[1];
    inputs_[2] = inputs_[1];
    inputs_[1] = inputs_[0];
    outputs_[2] = outputs_[1];
    outputs_[1] = *samples;
  }
 
  lastFrame_[0] = outputs_[1];
  return frames;
}

◆ tick() [2/2]

StkFrames & stk::BiQuad::tick	(	StkFrames &	iFrames,
		StkFrames &	oFrames,
		unsigned int	iChannel = `0`,
		unsigned int	oChannel = `0`
	)

inline

Take a channel of the iFrames object as inputs to the filter and write outputs to the oFrames object.

The iFrames object reference is returned. Each channel argument must be less than the number of channels in the corresponding StkFrames argument (the first channel is specified by 0). However, range checking is only performed if STK_DEBUG is defined during compilation, in which case an out-of-range value will trigger an StkError exception.

{
#if defined(_STK_DEBUG_)
  if ( iChannel >= iFrames.channels() || oChannel >= oFrames.channels() ) {
    oStream_ << "BiQuad::tick(): channel and StkFrames arguments are incompatible!";
    handleError( StkError::FUNCTION_ARGUMENT );
  }
#endif
 
  StkFloat *iSamples = &iFrames[iChannel];
  StkFloat *oSamples = &oFrames[oChannel];
  unsigned int iHop = iFrames.channels(), oHop = oFrames.channels();
  for ( unsigned int i=0; i<iFrames.frames(); i++, iSamples += iHop, oSamples += oHop ) {
    inputs_[0] = gain_ * *iSamples;
    *oSamples = b_[0] * inputs_[0] + b_[1] * inputs_[1] + b_[2] * inputs_[2];
    *oSamples -= a_[2] * outputs_[2] + a_[1] * outputs_[1];
    inputs_[2] = inputs_[1];
    inputs_[1] = inputs_[0];
    outputs_[2] = outputs_[1];
    outputs_[1] = *oSamples;
  }
 
  lastFrame_[0] = outputs_[1];
  return iFrames;
}

The documentation for this class was generated from the following file:

BiQuad.h

Public Member Functions

Additional Inherited Members