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#include <BlitSquare.h>
Inheritance diagram for BlitSquare:
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. |
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Set the phase of the signal. Set the phase of the signal, in the range 0 to 1. |
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Get the current phase of the signal. Get the phase of the signal, in the range [0 to 1.0). |
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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. |
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