Home   Information   Classes   Download   Usage   Mail List   Requirements   Links   FAQ   Tutorial


Public Member Functions | List of all members
stk::BiQuad Class Reference

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

#include <BiQuad.h>

Inheritance diagram for stk::BiQuad:
stk::Filter stk::Stk

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.
 
StkFramestick (StkFrames &frames, unsigned int channel=0)
 Take a channel of the StkFrames object as inputs to the filter and replace with corresponding outputs.
 
StkFramestick (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 StkFrameslastFrame (void) const
 Return an StkFrames reference to the last output sample frame.
 
virtual StkFramestick (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.

206{
207#if defined(_STK_DEBUG_)
208 if ( channel >= frames.channels() ) {
209 oStream_ << "BiQuad::tick(): channel and StkFrames arguments are incompatible!";
210 handleError( StkError::FUNCTION_ARGUMENT );
211 }
212#endif
213
214 StkFloat *samples = &frames[channel];
215 unsigned int hop = frames.channels();
216 for ( unsigned int i=0; i<frames.frames(); i++, samples += hop ) {
217 inputs_[0] = gain_ * *samples;
218 *samples = b_[0] * inputs_[0] + b_[1] * inputs_[1] + b_[2] * inputs_[2];
219 *samples -= a_[2] * outputs_[2] + a_[1] * outputs_[1];
220 inputs_[2] = inputs_[1];
221 inputs_[1] = inputs_[0];
222 outputs_[2] = outputs_[1];
223 outputs_[1] = *samples;
224 }
225
226 lastFrame_[0] = outputs_[1];
227 return frames;
228}
static void handleError(const char *message, StkError::Type type)
Static function for error reporting and handling using c-strings.

◆ 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.

231{
232#if defined(_STK_DEBUG_)
233 if ( iChannel >= iFrames.channels() || oChannel >= oFrames.channels() ) {
234 oStream_ << "BiQuad::tick(): channel and StkFrames arguments are incompatible!";
235 handleError( StkError::FUNCTION_ARGUMENT );
236 }
237#endif
238
239 StkFloat *iSamples = &iFrames[iChannel];
240 StkFloat *oSamples = &oFrames[oChannel];
241 unsigned int iHop = iFrames.channels(), oHop = oFrames.channels();
242 for ( unsigned int i=0; i<iFrames.frames(); i++, iSamples += iHop, oSamples += oHop ) {
243 inputs_[0] = gain_ * *iSamples;
244 *oSamples = b_[0] * inputs_[0] + b_[1] * inputs_[1] + b_[2] * inputs_[2];
245 *oSamples -= a_[2] * outputs_[2] + a_[1] * outputs_[1];
246 inputs_[2] = inputs_[1];
247 inputs_[1] = inputs_[0];
248 outputs_[2] = outputs_[1];
249 outputs_[1] = *oSamples;
250 }
251
252 lastFrame_[0] = outputs_[1];
253 return iFrames;
254}

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

The Synthesis ToolKit in C++ (STK)
©1995--2023 Perry R. Cook and Gary P. Scavone. All Rights Reserved.