add support for different filter types in biquad

include/BiQuad.h

@@ -74,6 +74,46 @@ public:
   */
   void setNotch( StkFloat frequency, StkFloat radius );
 
+  //! Set the filter coefficients for a low-pass at \e frequency (in Hz) with factor \e Q.
+  /*!
+    This method determines the filter coefficients corresponding to
+    a low-pass filter with cutoff placed at \e frequency and
+    Q-factor set by \e Q. Both \e frequency and \e Q must be positive.
+  */
+  void setLowPass( StkFloat frequency, StkFloat Q );
+
+  //! Set the filter coefficients for a high-pass at \e frequency (in Hz) with factor \e Q.
+  /*!
+    This method determines the filter coefficients corresponding to
+    a high-pass filter with cutoff placed at \e frequency and
+    Q-factor set by \e Q. Both \e frequency and \e Q must be positive.
+  */
+  void setHighPass( StkFloat frequency, StkFloat Q );
+
+  //! Set the filter coefficients for a band-pass at \e frequency (in Hz) with factor \e Q.
+  /*!
+    This method determines the filter coefficients corresponding to
+    a band-pass filter with center placed at \e frequency and
+    Q-factor set by \e Q. Both \e frequency and \e Q must be positive.
+  */
+  void setBandPass( StkFloat frequency, StkFloat Q );
+
+  //! Set the filter coefficients for a band-reject at \e frequency (in Hz) with factor \e Q.
+  /*!
+    This method determines the filter coefficients corresponding to
+    a band-reject filter with center placed at \e frequency and
+    Q-factor set by \e Q. Both \e frequency and \e Q must be positive.
+  */
+  void setBandReject( StkFloat frequency, StkFloat Q );
+
+  //! Set the filter coefficients for an all-pass at \e frequency (in Hz) with factor \e Q.
+  /*!
+    This method determines the filter coefficients corresponding to
+    an all-pass filter with center placed at \e frequency and
+    Q-factor set by \e Q. Both \e frequency and \e Q must be positive.
+  */
+  void setAllPass( StkFloat frequency, StkFloat Q );
+
   //! Sets the filter zeroes for equal resonance gain.
   /*!
     When using the filter as a resonator, zeroes places at z = 1, z
@@ -114,6 +154,14 @@ public:
  protected:
 
   virtual void sampleRateChanged( StkFloat newRate, StkFloat oldRate );
+  
+  // Helper function to update the three intermediate values for the predefined filter types
+  // along with the feedback filter coefficients. Performs the debug check for frequency and Q-factor arguments.
+  void setCommonFilterValues( StkFloat frequency, StkFloat Q );
+
+  StkFloat K_;
+  StkFloat kSqr_;
+  StkFloat denom_;
 };
 
 inline StkFloat BiQuad :: tick( StkFloat input )

src/BiQuad.cpp

@@ -24,6 +24,10 @@ BiQuad :: BiQuad() : Filter()
   inputs_.resize( 3, 1, 0.0 );
   outputs_.resize( 3, 1, 0.0 );
 
+  K_ = 0.0;
+  kSqr_ = 0.0;
+  denom_ = 1.0;
+
   Stk::addSampleRateAlert( this );
 }
 
@@ -73,6 +77,11 @@ void BiQuad :: setResonance( StkFloat frequency, StkFloat radius, bool normalize
     b_[1] = 0.0;
     b_[2] = -b_[0];
   }
+  else {
+    b_[0] = 1.0;
+    b_[1] = 0.0;
+    b_[2] = 0.0;
+  }
 }
 
 void BiQuad :: setNotch( StkFloat frequency, StkFloat radius )
@@ -93,6 +102,51 @@ void BiQuad :: setNotch( StkFloat frequency, StkFloat radius )
   b_[1] = (StkFloat) -2.0 * radius * cos( TWO_PI * (double) frequency / Stk::sampleRate() );
 }
 
+void BiQuad :: setLowPass( StkFloat frequency, StkFloat Q )
+{
+  setCommonFilterValues(frequency, Q);
+
+  b_[0] = kSqr_ * Q * denom_;
+  b_[1] = 2 * b_[0];
+  b_[2] = b_[0];
+}
+
+void BiQuad :: setHighPass( StkFloat frequency, StkFloat Q )
+{
+  setCommonFilterValues(frequency, Q);
+
+  b_[0] = Q * denom_;
+  b_[1] = -2 * b_[0];
+  b_[2] = b_[0];
+}
+
+void BiQuad :: setBandPass( StkFloat frequency, StkFloat Q )
+{
+  setCommonFilterValues(frequency, Q);
+
+  b_[0] = K_ * denom_;
+  b_[1] = 0.0;
+  b_[2] = -b_[0];
+}
+
+void BiQuad :: setBandReject( StkFloat frequency, StkFloat Q )
+{
+  setCommonFilterValues(frequency, Q);
+
+  b_[0] = Q * (kSqr_ + 1) * denom_;
+  b_[1] = 2 * Q * (kSqr_ - 1) * denom_;
+  b_[2] = b_[0];
+}
+
+void BiQuad :: setAllPass( StkFloat frequency, StkFloat Q )
+{
+  setCommonFilterValues(frequency, Q);
+
+  b_[0] = a_[2];
+  b_[1] = a_[1];
+  b_[2] = 1;
+}
+
 void BiQuad :: setEqualGainZeroes( void )
 {
   b_[0] = 1.0;
@@ -100,4 +154,25 @@ void BiQuad :: setEqualGainZeroes( void )
   b_[2] = -1.0;
 }
 
+void BiQuad :: setCommonFilterValues( StkFloat frequency, StkFloat Q)
+{
+#if defined(_STK_DEBUG_)
+  if ( frequency < 0.0 ) {
+    oStream_ << "BiQuad::updateKValues: frequency argument (" << frequency << ") is negative!";
+    handleError( StkError::WARNING ); return;
+  }
+   if ( Q < 0.0 ) {
+    oStream_ << "BiQuad::updateKValues: Q argument (" << Q << ") is negative!";
+    handleError( StkError::WARNING ); return;
+  }
+#endif
+
+  K_ = tan(PI * frequency / Stk::sampleRate());
+  kSqr_ = K_ * K_;
+  denom_ = 1 / (kSqr_ * Q + K_ + Q);
+
+  a_[1] = 2 * Q * (kSqr_ - 1) * denom_;
+  a_[2] = (kSqr_ * Q - K_ + Q) * denom_;
+}
+
 } // stk namespace