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BlitSquare Class Reference

#include <BlitSquare.h>

Inheritance diagram for BlitSquare:

Generator Stk List of all members.

Detailed Description

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 so a DC blocking filter is applied at the output.

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). Also note that the harmonics of a square wave fall at odd integer multiples of the fundamental, so aliasing will happen with a lower fundamental than with the other Blit waveforms. This class is not guaranteed to be well behaved in the presence of significant aliasing.

Based on initial code of Robin Davies, 2005. Modified algorithm code by Gary Scavone, 2005 - 2006.


Public Member Functions

 BlitSquare (StkFloat frequency=220.0)
 Default constructor that initializes BLIT frequency to 220 Hz.
 ~BlitSquare ()
 Class destructor.
void reset ()
 Resets the oscillator state and phase to 0.
void setPhase (StkFloat phase)
 Set the phase of the signal.
StkFloat getPhase () const
 Get the current phase of the signal.
void setFrequency (StkFloat frequency)
 Set the impulse train rate in terms of a frequency in Hz.
void setHarmonics (unsigned int nHarmonics=0)
 Set the number of harmonics generated in the signal.


Member Function Documentation

void BlitSquare::setPhase StkFloat  phase  )  [inline]
 

Set the phase of the signal.

Set the phase of the signal, in the range 0 to 1.

StkFloat BlitSquare::getPhase  )  const [inline]
 

Get the current phase of the signal.

Get the phase of the signal, in the range [0 to 1.0).

void BlitSquare::setHarmonics unsigned int  nHarmonics = 0  ) 
 

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.


The documentation for this class was generated from the following file:
The Synthesis ToolKit in C++ (STK)
©1995-2007 Perry R. Cook and Gary P. Scavone. All Rights Reserved.