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https://github.com/thestk/stk
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85 lines
2.3 KiB
C++
85 lines
2.3 KiB
C++
/***************************************************/
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/*! \class Asymp
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\brief STK asymptotic curve envelope class
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This class implements a simple envelope generator
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which asymptotically approaches a target value.
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The algorithm used is of the form:
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x[n] = a x[n-1] + (1-a) target,
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where a = exp(-T/tau), T is the sample period, and
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tau is a time constant. The user can set the time
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constant (default value = 0.3) and target value.
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Theoretically, this recursion never reaches its
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target, though the calculations in this class are
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stopped when the current value gets within a small
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threshold value of the target (at which time the
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current value is set to the target). It responds
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to \e keyOn and \e keyOff messages by ramping to
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1.0 on keyOn and to 0.0 on keyOff.
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by Perry R. Cook and Gary P. Scavone, 1995 - 2004.
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*/
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/***************************************************/
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#ifndef STK_ASYMP_H
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#define STK_ASYMP_H
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#include "Envelope.h"
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const StkFloat TARGET_THRESHOLD = 0.000001;
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class Asymp : public Envelope
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{
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public:
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//! Default constructor.
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Asymp(void);
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//! Class destructor.
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~Asymp(void);
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//! Set target = 1.
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void keyOn(void);
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//! Set target = 0.
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void keyOff(void);
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//! Set the asymptotic rate via the time factor \e tau (must be > 0).
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/*!
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The rate is computed as described above. The value of \e tau
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must be greater than zero. Values of \e tau close to zero produce
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fast approach rates, while values greater than 1.0 produce rather
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slow rates.
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*/
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void setTau(StkFloat tau);
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//! Set the asymptotic rate based on a time duration (must be > 0).
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void setTime(StkFloat time);
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//! Set the target value.
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void setTarget(StkFloat target);
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//! Return one envelope output value.
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StkFloat tick(void);
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//! Compute \e vectorSize outputs and return them in \e vector.
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StkFloat *tick( StkFloat *vector, unsigned int vectorSize );
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//! Fill a channel of the StkFrames object with computed outputs.
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/*!
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The \c channel argument should be one or greater (the first
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channel is specified by 1). An StkError will be thrown if the \c
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channel argument is zero or it is greater than the number of
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channels in the StkFrames object.
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*/
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StkFrames& tick( StkFrames& frames, unsigned int channel = 1 );
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protected:
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StkFloat factor_;
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StkFloat constant_;
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};
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#endif
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