compressor.c

#include "compressor.h"

float gainComputedComp;
float gainSmootedComp;

dynamic_compressor_t generate_compressor(
    float threshold,
    float ratio,
    float width,
    float attack,
    float release,
    float gain,
    uint16_t samplerate)
{
    float glin = powf(10.0f, (gain / 20.0f)) - 1.0f;

    double lnine = log10(9.0f);
    float alphaA = expf(-lnine / (attack * samplerate));
    float alphaR = expf(-lnine / (release * samplerate));
    float OMalphaA = (1 - alphaA);
    float OMalphaR = (1 - alphaR);

    dynamic_compressor_t c = {
        .alphaA = alphaA,
        .alphaR = alphaR,
        .OMalphaA = OMalphaA,
        .OMalphaR = OMalphaR,

        .ratio = ratio,
        .width = width,
        .gain = glin,
        .threshold = threshold,

        .gs = 1.0f,
    };

    return c;
}

void dynamic_compressor(sample_t *s, dynamic_compressor_t *c)
{
    float xnormal = fabsf(*s);
    float xdb = 20.0f * log10f(xnormal);

    // gain computer
    float xsc = 0.0f;
    if (xdb < (c->threshold - (c->width / 2)))
    {
        xsc = xdb;
    }
    else if (((c->threshold - (c->width / 2)) <= xdb) && (xdb <= (c->threshold + (c->width / 2))))
    {
        xsc = xdb + (((1 / c->ratio) - 1) * \
        ( (xdb - c->threshold + (c->width / 2)) * (xdb - c->threshold + (c->width / 2)) )   ) / \
        (2 * c->width);
    }
    else if (xdb > (c->threshold + (c->width / 2)))
    {
        xsc = c->threshold + ((xdb - c->threshold) / c->ratio);
    }
    gainComputedComp = xsc - xdb;

    // smoothing
    if (gainComputedComp <= gainSmootedComp)
    {
        gainSmootedComp = c->alphaA * gainSmootedComp + c->OMalphaA * gainComputedComp;
    }
    else if (gainComputedComp > gainSmootedComp)
    {
        gainSmootedComp = c->alphaR * gainSmootedComp + c->OMalphaR * gainComputedComp;
    }

    // makeup
    c->gs = gainSmootedComp;
    gainSmootedComp += c->gain;

    // apply
    float glin = powFastLookup(gainSmootedComp / 20.0f, BASE10);
    // float glin = powf(10.0f, gainSmootedComp / 20.0f);
    *s = (*s) * glin;
}