MicroDexed is a compatible 6-operator-FM-synth based on the Teensy(-3.6/-4.x) Microcontroller. https://www.parasitstudio.de
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/*
* Copyright 2013 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define _USE_MATH_DEFINES
#include <math.h>
#include "synth.h"
#include "exp2.h"
#include <stdio.h>
#ifdef _MSC_VER
#define exp2(arg) pow(2.0, arg)
#endif
int32_t exp2tab[EXP2_N_SAMPLES << 1];
void Exp2::init() {
FRAC_NUM inc = exp2(1.0 / EXP2_N_SAMPLES);
FRAC_NUM y = 1 << 30;
for (int i = 0; i < EXP2_N_SAMPLES; i++) {
exp2tab[(i << 1) + 1] = (int32_t)floor(y + 0.5);
y *= inc;
}
for (int i = 0; i < EXP2_N_SAMPLES - 1; i++) {
exp2tab[i << 1] = exp2tab[(i << 1) + 3] - exp2tab[(i << 1) + 1];
}
exp2tab[(EXP2_N_SAMPLES << 1) - 2] = (1U << 31) - exp2tab[(EXP2_N_SAMPLES << 1) - 1];
}
int32_t tanhtab[TANH_N_SAMPLES << 1];
static FRAC_NUM dtanh(FRAC_NUM y) {
return 1 - y * y;
}
void Tanh::init() {
FRAC_NUM step = 4.0 / TANH_N_SAMPLES;
FRAC_NUM y = 0;
for (int i = 0; i < TANH_N_SAMPLES; i++) {
tanhtab[(i << 1) + 1] = (1 << 24) * y + 0.5;
//printf("%d\n", tanhtab[(i << 1) + 1]);
// Use a basic 4th order Runge-Kutte to compute tanh from its
// differential equation.
FRAC_NUM k1 = dtanh(y);
FRAC_NUM k2 = dtanh(y + 0.5 * step * k1);
FRAC_NUM k3 = dtanh(y + 0.5 * step * k2);
FRAC_NUM k4 = dtanh(y + step * k3);
FRAC_NUM dy = (step / 6) * (k1 + k4 + 2 * (k2 + k3));
y += dy;
}
for (int i = 0; i < TANH_N_SAMPLES - 1; i++) {
tanhtab[i << 1] = tanhtab[(i << 1) + 3] - tanhtab[(i << 1) + 1];
}
int32_t lasty = (1 << 24) * y + 0.5;
tanhtab[(TANH_N_SAMPLES << 1) - 2] = lasty - tanhtab[(TANH_N_SAMPLES << 1) - 1];
}