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https://github.com/thestk/stk
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115 lines
2.7 KiB
C++
115 lines
2.7 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 - 2007.
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*/
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/***************************************************/
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#include "Asymp.h"
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#include <cmath>
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Asymp :: Asymp(void) : Envelope()
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{
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factor_ = exp( -1.0 / ( 0.3 * Stk::sampleRate() ) );
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constant_ = 0.0;
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}
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Asymp :: ~Asymp(void)
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{
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}
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void Asymp :: sampleRateChanged( StkFloat newRate, StkFloat oldRate )
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{
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if ( !ignoreSampleRateChange_ ) {
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StkFloat tau = -1.0 / ( std::log( factor_ ) * oldRate );
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factor_ = std::exp( -1.0 / ( tau * newRate ) );
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}
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}
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void Asymp :: keyOn(void)
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{
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Envelope::keyOn();
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constant_ = ( 1.0 - factor_ ) * target_;
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}
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void Asymp :: keyOff(void)
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{
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Envelope::keyOff();
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constant_ = ( 1.0 - factor_ ) * target_;
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}
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void Asymp :: setTau(StkFloat tau)
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{
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if (tau <= 0.0) {
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errorString_ << "Asymp::setTau: negative or zero tau not allowed ... ignoring!";
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handleError( StkError::WARNING );
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return;
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}
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factor_ = std::exp( -1.0 / ( tau * Stk::sampleRate() ) );
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constant_ = ( 1.0 - factor_ ) * target_;
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}
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void Asymp :: setTime(StkFloat time)
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{
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if (time <= 0.0) {
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errorString_ << "Asymp::setTime: negative or zero times not allowed ... ignoring!";
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handleError( StkError::WARNING );
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return;
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}
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StkFloat tau = -time / std::log( TARGET_THRESHOLD );
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factor_ = std::exp( -1.0 / ( tau * Stk::sampleRate() ) );
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constant_ = ( 1.0 - factor_ ) * target_;
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}
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void Asymp :: setTarget(StkFloat target)
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{
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Envelope::setTarget( target );
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constant_ = ( 1.0 - factor_ ) * target_;
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}
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StkFloat Asymp :: computeSample(void)
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{
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if (state_) {
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value_ = factor_ * value_ + constant_;
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// Check threshold.
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if ( target_ > value_ ) {
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if ( target_ - value_ <= TARGET_THRESHOLD ) {
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value_ = target_;
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state_ = 0;
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}
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}
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else {
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if ( value_ - target_ <= TARGET_THRESHOLD ) {
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value_ = target_;
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state_ = 0;
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}
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}
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}
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lastOutput_ = value_;
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return value_;
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}
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