qmk-firmware/quantum/audio/voices.c

#include "voices.h"

extern uint16_t envelope_index;
extern float note_timbre;

voice_type voice = default_voice;

void set_voice(voice_type v) {
    voice = v;
}

float voice_envelope(float frequency) {
    // envelope_index ranges from 0 to 0xFFFF, which is preserved at 880.0 Hz
    uint16_t compensated_index = (uint16_t)((float)envelope_index * (880.0 / frequency));

    switch (voice) {
        case default_voice:
            // nothing here on purpose
        break;
        case butts_fader:
            switch (compensated_index) {
                case 0 ... 9:
                    frequency = frequency / 4;
                    note_timbre = TIMBRE_12;
                break;
                case 10 ... 19:
                    frequency = frequency / 2;
                    note_timbre = TIMBRE_12;
                break;
                case 20 ... 200:
                    note_timbre = .125 - pow(((float)compensated_index - 20) / (200 - 20), 2)*.125;
                break;
                default:
                    note_timbre = 0;
                break;
            }
        break;
        case octave_crunch:
            switch (compensated_index) {
                case 0 ... 9:
                case 20 ... 24:
                case 30 ... 32:
                    frequency = frequency / 2;
                    note_timbre = TIMBRE_12;
                break;
                case 10 ... 19:
                case 25 ... 29:
                case 33 ... 35:
                    frequency = frequency * 2;
                    note_timbre = TIMBRE_12;
                break;
                default:
                    note_timbre = TIMBRE_12;
                break;
            }
        break;
    }

    return frequency;
}