stk::TwoPole Class Reference

STK two-pole filter class. More...

#include <TwoPole.h>

Inheritance diagram for stk::TwoPole:

Public Member Functions
	TwoPole (void)
	Default constructor creates a second-order pass-through filter.
	~TwoPole ()
	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	setB0 (StkFloat b0)
	Set the b[0] coefficient value.
void	setA1 (StkFloat a1)
	Set the a[1] coefficient value.
void	setA2 (StkFloat a2)
	Set the a[2] coefficient value.
void	setCoefficients (StkFloat b0, StkFloat a1, StkFloat a2, bool clearState=false)
	Set all filter coefficients.
void	setResonance (StkFloat frequency, StkFloat radius, bool normalize=false)
	Sets the filter coefficients for a resonance at frequency (in Hz).
StkFloat	lastOut (void) const
	Return the last computed output value.
StkFloat	tick (StkFloat input)
	Input one sample to the filter and return 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 two-pole filter class.

This class implements a two-pole digital filter. A method is provided for creating a resonance in the frequency response while maintaining a nearly constant filter gain.

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

Member Function Documentation

setResonance()

void stk::TwoPole::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 coefficients are then normalized to produce unity gain at frequency (the actual maximum filter gain tends to be slightly greater than unity when radius is not close to one). 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. For a better resonance filter, use a BiQuad filter.

See also

BiQuad filter class

tick() [1/2]

StkFrames & stk::TwoPole::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_ << "TwoPole::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] - a_[1] * outputs_[1] - a_[2] * outputs_[2];
    outputs_[2] = outputs_[1];
    outputs_[1] = *samples;
  }
 
  lastFrame_[0] = outputs_[1];
  return frames;
}

tick() [2/2]

StkFrames & stk::TwoPole::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_ << "TwoPole::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] - a_[1] * outputs_[1] - a_[2] * outputs_[2];
    outputs_[2] = outputs_[1];
    outputs_[1] = *oSamples;
  }
 
  lastFrame_[0] = outputs_[1];
  return iFrames;
}

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

• TwoPole.h