Version 4.2.1

include/BlitSquare.h

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+/***************************************************/
+/*! \class BlitSquare
+    \brief STK band-limited square wave class.
+
+    This class generates a band-limited square wave signal.  It is
+    derived in part from the approach reported by Stilson and Smith in
+    "Alias-Free Digital Synthesis of Classic Analog Waveforms", 1996.
+    The algorithm implemented in this class uses a SincM function with
+    an even M value to achieve a bipolar bandlimited impulse train.
+    This signal is then integrated to achieve a square waveform.  The
+    integration process has an associated DC offset but that is
+    subtracted off the output signal.
+
+    The user can specify both the fundamental frequency of the
+    waveform and the number of harmonics contained in the resulting
+    signal.
+
+    If nHarmonics is 0, then the signal will contain all harmonics up
+    to half the sample rate.  Note, however, that this setting may
+    produce aliasing in the signal when the frequency is changing (no
+    automatic modification of the number of harmonics is performed by
+    the setFrequency() function).
+
+    Based on initial code of Robin Davies, 2005.
+    Modified algorithm code by Gary Scavone, 2005.
+*/
+/***************************************************/
+
+#ifndef STK_BLITSQUARE_H
+#define STK_BLITSQUARE_H
+
+#include "Generator.h"
+
+class BlitSquare: public Generator
+{
+ public:
+  //! Default constructor that initializes BLIT frequency to 220 Hz.
+  BlitSquare( StkFloat frequency = 220.0 );
+
+  //! Class destructor.
+  ~BlitSquare();
+
+  //! Resets the oscillator state and phase to 0.
+  void reset();
+
+  //! Set the phase of the signal.
+  /*!
+    Set the phase of the signal, in the range 0 to 1.
+  */
+  void setPhase( StkFloat phase ) { phase_ = PI * phase; };
+
+  //! Get the current phase of the signal.
+  /*!
+    Get the phase of the signal, in the range [0 to 1.0).
+  */
+  StkFloat getPhase() const { return phase_ / PI; };
+
+  //! Set the impulse train rate in terms of a frequency in Hz.
+  void setFrequency( StkFloat frequency );
+
+  //! Set the number of harmonics generated in the signal.
+  /*!
+    This function sets the number of harmonics contained in the
+    resulting signal.  It is equivalent to (2 * M) + 1 in the BLIT
+    algorithm.  The default value of 0 sets the algorithm for maximum
+    harmonic content (harmonics up to half the sample rate).  This
+    parameter is not checked against the current sample rate and
+    fundamental frequency.  Thus, aliasing can result if one or more
+    harmonics for a given fundamental frequency exceeds fs / 2.  This
+    behavior was chosen over the potentially more problematic solution
+    of automatically modifying the M parameter, which can produce
+    audible clicks in the signal.
+  */
+  void setHarmonics( unsigned int nHarmonics = 0 );
+
+ protected:
+
+  void updateHarmonics( void );
+  StkFloat computeSample( void );
+
+  unsigned int nHarmonics_;
+  unsigned int m_;
+  StkFloat rate_;
+  StkFloat phase_;
+  StkFloat p_;
+  StkFloat offset_;
+};
+
+#endif