dexed/Source/PluginFx.cpp

/*
  ==============================================================================

    PluginFx.cpp
    Created: 26 Dec 2013 7:13:29pm
    Author:  Pascal Gauthier

    The LPF is taken from the PD moog~ object. (David Lowenfels) 
    Code is based off of Tim Stilson's moog filter code
 
  ==============================================================================
*/
#define _USE_MATH_DEFINES
#include <math.h>
#include "PluginFx.h"
#include "PluginProcessor.h"

static float gaintable[199] = {
    0.999969, 0.990082, 0.980347, 0.970764, 0.961304, 0.951996, 0.94281, 0.933777, 0.924866, 0.916077, 0.90741, 0.898865, 0.890442,
    0.882141, 0.873962, 0.865906, 0.857941, 0.850067, 0.842346, 0.834686, 0.827148, 0.819733, 0.812378, 0.805145, 0.798004, 0.790955,
    0.783997, 0.77713, 0.770355, 0.763672, 0.75708 , 0.75058, 0.744141, 0.737793, 0.731537, 0.725342, 0.719238, 0.713196, 0.707245,
    0.701355, 0.695557, 0.689819, 0.684174, 0.678558, 0.673035, 0.667572, 0.66217, 0.65686, 0.651581, 0.646393, 0.641235, 0.636169,
    0.631134, 0.62619, 0.621277, 0.616425, 0.611633, 0.606903, 0.602234, 0.597626, 0.593048, 0.588531, 0.584045, 0.579651, 0.575287,
    0.570953, 0.566681, 0.562469, 0.558289, 0.554169, 0.550079, 0.546051, 0.542053, 0.538116, 0.53421, 0.530334, 0.52652, 0.522736,
    0.518982, 0.515289, 0.511627, 0.507996 , 0.504425, 0.500885, 0.497375, 0.493896, 0.490448, 0.487061, 0.483704, 0.480377, 0.477081,
    0.473816, 0.470581, 0.467377, 0.464203, 0.46109, 0.457977, 0.454926, 0.451874, 0.448883, 0.445892, 0.442932, 0.440033, 0.437134,
    0.434265, 0.431427, 0.428619, 0.425842, 0.423096, 0.42038, 0.417664, 0.415009, 0.412354, 0.409729, 0.407135, 0.404572, 0.402008,
    0.399506, 0.397003, 0.394501, 0.392059, 0.389618, 0.387207, 0.384827, 0.382477, 0.380127, 0.377808, 0.375488, 0.37323, 0.370972,
    0.368713, 0.366516, 0.364319, 0.362122, 0.359985, 0.357849, 0.355713, 0.353607, 0.351532, 0.349457, 0.347412, 0.345398, 0.343384,
    0.34137, 0.339417, 0.337463, 0.33551, 0.333588, 0.331665, 0.329773, 0.327911, 0.32605, 0.324188, 0.322357, 0.320557, 0.318756,
    0.316986, 0.315216, 0.313446, 0.311707, 0.309998, 0.308289, 0.30658, 0.304901, 0.303223, 0.301575, 0.299927, 0.298309, 0.296692,
    0.295074, 0.293488, 0.291931, 0.290375, 0.288818, 0.287262, 0.285736, 0.284241, 0.282715, 0.28125, 0.279755, 0.27829, 0.276825,
    0.275391, 0.273956, 0.272552, 0.271118, 0.269745, 0.268341, 0.266968, 0.265594, 0.264252, 0.262909, 0.261566, 0.260223, 0.258911,
    0.257599, 0.256317, 0.255035, 0.25375
};

static inline float saturate(float input) { //clamp without branching
#define _limit 0.95
    float x1 = fabsf( input + _limit );
    float x2 = fabsf( input - _limit );
    return 0.5 * (x1 - x2);
}

static inline float crossfade(float amount, float a, float b) {
    return (1-amount) * a + amount * b;
}

void PluginFx::init(int sampleRate) {
    uiCutoff = 1;
    uiReso = 0;
    srate = sampleRate;
    output = 0;
    for(int i=0;i<4;i++)
        state[i] = 0;
}

void PluginFx::process(float *work, int sampleSize) {

    // don't apply the LPF if the cutoff is to maximum
    if ( uiCutoff == 1 )
        return;
    
    // the UI values haved changed
    if ( uiCutoff != pCutoff || uiReso != pReso) {
        // calc cutoff
        // mel scale freq : http://www.speech.kth.se/~giampi/auditoryscales/
        float freqCutoff = 700 * (pow(M_E,(uiCutoff*4000/1127)-1)) + 20;
        float fc = 2 * freqCutoff / srate;
        float x2 = fc*fc;
        float x3 = fc*x2;
        p = -0.69346 * x3 - 0.59515 * x2 + 3.2937 * fc - 1.0072; //cubic fit

        // calc reso
        float ix = p * 99;
        int ixint = floor( ix );
        float ixfrac = ix - ixint;
        Q = uiReso * crossfade( ixfrac, gaintable[ ixint + 99 ], gaintable[ ixint + 100 ] );

        pCutoff = uiCutoff;
        pReso = uiReso;
    }
  
    for (int i=0; i < sampleSize; i++ ) {
        output = 0.10 * ( work[i] - output ); //negative feedback
        for(int pole=0; pole < 4; pole++) {
            float temp = state[pole];
            output = saturate( output + p * (output - temp));
            state[pole] = output;
            output = saturate( output + temp );
        }
        work[i] = output;
        output *= Q;  //scale the feedback
    }
}