stk::BiQuad Class Reference

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). More...
void	setNotch (StkFloat frequency, StkFloat radius)
	Set the filter coefficients for a notch at frequency (in Hz). More...
void	setEqualGainZeroes (void)
	Sets the filter zeroes for equal resonance gain. More...
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. More...
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. More...
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. More...
StkFloat	getGain (void) const
	Return the current filter gain.
StkFloat	phaseDelay (StkFloat frequency)
	Return the filter phase delay at the specified frequency. More...
const StkFrames &	lastFrame (void) const
	Return an StkFrames reference to the last output sample frame.

Static Public Member Functions
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. More...
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
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
void	handleError (StkError::Type type) const
	Internal function for error reporting that assumes message in oStream_ variable.
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.

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.

by Perry R. Cook and Gary P. Scavone, 1995–2019.

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.

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;
}

setGain()

void stk::Filter::setGain ( StkFloat  gain )

inlineinherited

Set the filter gain.

The gain is applied at the filter input and does not affect the coefficient values. The default gain value is 1.0.

{ gain_ = gain; };

phaseDelay()

StkFloat stk::Filter::phaseDelay ( StkFloat  frequency )

inlineinherited

Return the filter phase delay at the specified frequency.

Note that the phase delay calculation accounts for the filter gain. The frequency value should be greater than 0.0 and less than or equal to one-half the sample rate.

{
  if ( frequency <= 0.0 || frequency > 0.5 * Stk::sampleRate() ) {
    oStream_ << "Filter::phaseDelay: argument (" << frequency << ") is out of range!";
    handleError( StkError::WARNING ); return 0.0;
  }
 
  StkFloat omegaT = 2 * STK_PI * frequency / Stk::sampleRate();
  StkFloat real = 0.0, imag = 0.0;
  for ( unsigned int i=0; i<b_.size(); i++ ) {
    real += b_[i] * std::cos( i * omegaT );
    imag -= b_[i] * std::sin( i * omegaT );
  }
  real *= gain_;
  imag *= gain_;
 
  StkFloat phase = atan2( imag, real );
 
  real = 0.0, imag = 0.0;
  for ( unsigned int i=0; i<a_.size(); i++ ) {
    real += a_[i] * std::cos( i * omegaT );
    imag -= a_[i] * std::sin( i * omegaT );
  }
 
  phase -= std::atan2( imag, real );
  phase = std::fmod( -phase, 2 * STK_PI );
  return phase / omegaT;
}

setSampleRate()

static void stk::Stk::setSampleRate ( StkFloat  rate )

staticinherited

Static method that sets the STK sample rate.

The sample rate set using this method is queried by all STK classes that depend on its value. It is initialized to the default SRATE set in Stk.h. Many STK classes use the sample rate during instantiation. Therefore, if you wish to use a rate that is different from the default rate, it is imperative that it be set BEFORE STK objects are instantiated. A few classes that make use of the global STK sample rate are automatically notified when the rate changes so that internal class data can be appropriately updated. However, this has not been fully implemented. Specifically, classes that appropriately update their own data when either a setFrequency() or noteOn() function is called do not currently receive the automatic notification of rate change. If the user wants a specific class instance to ignore such notifications, perhaps in a multi-rate context, the function Stk::ignoreSampleRateChange() should be called.

Member Data Documentation

STK_SINT8

const StkFormat stk::Stk::STK_SINT8

staticinherited

-128 to +127

STK_SINT16

const StkFormat stk::Stk::STK_SINT16

staticinherited

-32768 to +32767

STK_SINT24

const StkFormat stk::Stk::STK_SINT24

staticinherited

Lower 3 bytes of 32-bit signed integer.

STK_SINT32

const StkFormat stk::Stk::STK_SINT32

staticinherited

-2147483648 to +2147483647.

STK_FLOAT32

const StkFormat stk::Stk::STK_FLOAT32

staticinherited

Normalized between plus/minus 1.0.

STK_FLOAT64

const StkFormat stk::Stk::STK_FLOAT64

staticinherited

Normalized between plus/minus 1.0.

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

• BiQuad.h