stfu/Source/Instruments/Trojka/trojka.c

#if defined(STFU_MAIN) && !defined(STFU_TROJKA)
#define STFU_TROJKA

#include "../../config.h"
#include "../../envelope.c"
#include "../../phaser.c"

#define STFU_TROJKA_OP_COUNT 3

/* https://multimed.org/student/eim/en/04-FM.pdf */

// todo: A few more algorithm configurations.
// todo: Other oscillators.

struct stfu_trojka {
  struct stfu_phaser phasers[STFU_TROJKA_OP_COUNT];
  struct stfu_envelope envelopes[STFU_TROJKA_OP_COUNT];
  float gains[STFU_TROJKA_OP_COUNT]; // todo: Combine with indices?
  float freq_scales[STFU_TROJKA_OP_COUNT];
  float indices[STFU_TROJKA_OP_COUNT - 1]; /* 1 to 100 */
  float key_frequency;
  float feedback_gain; // todo: Separate gain for channels?
  float left_feedback, right_feedback;
};

static struct stfu_trojka stfu_sample_trojka(struct stfu_trojka synth,
                                             float buffer[static 2]) {
  for (int i = 0; i < STFU_TROJKA_OP_COUNT; ++i) {
    synth.phasers[i] = stfu_pump_phaser(synth.phasers[i]);
    synth.envelopes[i] = stfu_pump_envelope(synth.envelopes[i]);
  }

  float left_modulator_stack =
      synth.envelopes[1].v * synth.indices[1] *
          sinf(synth.phasers[1].v + synth.envelopes[0].v * synth.indices[0] *
                                        sinf(synth.phasers[0].v)) +
      synth.left_feedback * synth.feedback_gain;
  float right_modulator_stack = left_modulator_stack;

  synth.left_feedback = left_modulator_stack;
  synth.right_feedback = right_modulator_stack;

  float left =
      synth.envelopes[2].v * sinf(synth.phasers[2].v + left_modulator_stack);
  float right =
      synth.envelopes[2].v * sinf(synth.phasers[2].v + right_modulator_stack);

  buffer[0] = left;
  buffer[1] = right;

  return synth;
}

static struct stfu_trojka stfu_press_trojka(struct stfu_trojka synth,
                                            float key_frequency) {
  for (int i = 0; i < STFU_TROJKA_OP_COUNT; ++i) {
    synth.phasers[i] = stfu_set_phaser_frequency(
        synth.phasers[i], key_frequency * synth.freq_scales[i]);
    synth.envelopes[i] = stfu_trigger_envelope(synth.envelopes[i]);
  }

  return synth;
}

#endif