view projects/d-box/ADSR.cpp @ 45:579c86316008 newapi

Major API overhaul. Moved to a single data structure for handling render functions. Functionally, generally similar except for scheduling within PRU loop function, which now uses interrupts from the PRU rather than polling. This requires an updated kernel.

//
//  ADSR.cpp
//
//  Created by Nigel Redmon on 12/18/12.
//  EarLevel Engineering: earlevel.com
//  Copyright 2012 Nigel Redmon
//
//  For a complete explanation of the ADSR envelope generator and code,
//  read the series of articles by the author, starting here:
//  http://www.earlevel.com/main/2013/06/01/envelope-generators/
//
//  License:
//
//  This source code is provided as is, without warranty.
//  You may copy and distribute verbatim copies of this document.
//  You may modify and use this source code to create binary code for your own purposes, free or commercial.
//

#include "ADSR.h"
#include <math.h>


ADSR::ADSR(void) {
    reset();
    setAttackRate(0);
    setDecayRate(0);
    setReleaseRate(0);
    setSustainLevel(1.0);
    setTargetRatioA(0.3);
    setTargetRatioDR(0.0001);
}

ADSR::~ADSR(void) {
}

void ADSR::setAttackRate(float rate) {
    attackRate = rate;
    attackCoef = calcCoef(rate, targetRatioA);
    attackBase = (1.0 + targetRatioA) * (1.0 - attackCoef);
}

void ADSR::setDecayRate(float rate) {
    decayRate = rate;
    decayCoef = calcCoef(rate, targetRatioDR);
    decayBase = (sustainLevel - targetRatioDR) * (1.0 - decayCoef);
}

void ADSR::setReleaseRate(float rate) {
    releaseRate = rate;
    releaseCoef = calcCoef(rate, targetRatioDR);
    releaseBase = -targetRatioDR * (1.0 - releaseCoef);
}

float ADSR::calcCoef(float rate, float targetRatio) {
    return exp(-log((1.0 + targetRatio) / targetRatio) / rate);
}

void ADSR::setSustainLevel(float level) {
    sustainLevel = level;
    decayBase = (sustainLevel - targetRatioDR) * (1.0 - decayCoef);
}

void ADSR::setTargetRatioA(float targetRatio) {
    if (targetRatio < 0.000000001)
        targetRatio = 0.000000001;  // -180 dB
    targetRatioA = targetRatio;
    attackBase = (1.0 + targetRatioA) * (1.0 - attackCoef);
}

void ADSR::setTargetRatioDR(float targetRatio) {
    if (targetRatio < 0.000000001)
        targetRatio = 0.000000001;  // -180 dB
    targetRatioDR = targetRatio;
    decayBase = (sustainLevel - targetRatioDR) * (1.0 - decayCoef);
    releaseBase = -targetRatioDR * (1.0 - releaseCoef);
}