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STK biquad (twopole, twozero) filter class. More...
#include <BiQuad.h>
Public Member Functions  
BiQuad ()  
Default constructor creates a secondorder passthrough 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 lowpass with cutoff frequency fc (in Hz) and Qfactor Q.  
void  setHighPass (StkFloat fc, StkFloat Q=RECIP_SQRT_2) 
Set the filter coefficients for a highpass with cutoff frequency fc (in Hz) and Qfactor Q.  
void  setBandPass (StkFloat fc, StkFloat Q) 
Set the filter coefficients for a bandpass centered at fc (in Hz) with Qfactor Q.  
void  setBandReject (StkFloat fc, StkFloat Q) 
Set the filter coefficients for a bandreject centered at fc (in Hz) with Qfactor Q.  
void  setAllPass (StkFloat fc, StkFloat Q) 
Set the filter coefficients for an allpass centered at fc (in Hz) with Qfactor 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 byteswaps a 16bit data type.  
static void  swap32 (unsigned char *ptr) 
Static method that byteswaps a 32bit data type.  
static void  swap64 (unsigned char *ptr) 
Static method that byteswaps a 64bit data type.  
static void  sleep (unsigned long milliseconds) 
Static crossplatform 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 cstrings.  
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.  
STK biquad (twopole, twozero) filter class.
This class implements a twopole, twozero 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.
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 complexconjugate poles with the given frequency (in Hz) and radius from the zplane 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 unitcircle (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.
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 complexconjugate zeros with the given frequency (in Hz) and radius from the zplane origin. No filter normalization is attempted. The frequency value should be between zero and half the sample rate. The radius value should be positive.
void stk::BiQuad::setLowPass  (  StkFloat  fc, 
StkFloat  Q = RECIP_SQRT_2 

) 
Set the filter coefficients for a lowpass with cutoff frequency fc (in Hz) and Qfactor Q.
This method determines the filter coefficients corresponding to a lowpass 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.
void stk::BiQuad::setHighPass  (  StkFloat  fc, 
StkFloat  Q = RECIP_SQRT_2 

) 
Set the filter coefficients for a highpass with cutoff frequency fc (in Hz) and Qfactor Q.
This method determines the filter coefficients corresponding to a highpass 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.
void stk::BiQuad::setBandPass  (  StkFloat  fc, 
StkFloat  Q  
) 
Set the filter coefficients for a bandpass centered at fc (in Hz) with Qfactor Q.
This method determines the filter coefficients corresponding to a bandpass filter with passband 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.
void stk::BiQuad::setBandReject  (  StkFloat  fc, 
StkFloat  Q  
) 
Set the filter coefficients for a bandreject centered at fc (in Hz) with Qfactor Q.
This method determines the filter coefficients corresponding to a bandreject filter with stopband 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.
void stk::BiQuad::setAllPass  (  StkFloat  fc, 
StkFloat  Q  
) 
Set the filter coefficients for an allpass centered at fc (in Hz) with Qfactor Q.
This method determines the filter coefficients corresponding to an allpass 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.
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.
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 outofrange value will trigger an StkError exception.
Implements stk::Filter.

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 outofrange value will trigger an StkError exception.
The Synthesis ToolKit in C++ (STK) 
©19952023 Perry R. Cook and Gary P. Scavone. All Rights Reserved. 