music-synthesizer-for-android/cpp/src/lfo.cc

/*
 * 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.
 */

// Low frequency oscillator, compatible with DX7

#include "synth.h"

#include "sin.h"
#include "lfo.h"

uint32_t Lfo::unit_;

void Lfo::init(double sample_rate) {
  // constant is 1 << 32 / 15.5s / 11
  Lfo::unit_ = (int32_t)(N * 25190424 / sample_rate + 0.5);
}

void Lfo::reset(const char params[6]) {
  int rate = params[0];  // 0..99
  int sr = rate == 0 ? 1 : (165 * rate) >> 6;
  sr *= sr < 160 ? 11 : (11 + ((sr - 160) >> 4));
  delta_ = unit_ * sr;
  int a = 99 - params[1];  // LFO delay
  if (a == 99) {
    delayinc_ = ~0u;
    delayinc2_ = ~0u;
  } else {
  a = (16 + (a & 15)) << (1 + (a >> 4));
    delayinc_ = unit_ * a;
    a &= 0xff80;
    a = max(0x80, a);
    delayinc2_ = unit_ * a;
  }
  waveform_ = params[5];
  sync_ = params[4] != 0;
}

int32_t Lfo::getsample() {
  phase_ += delta_;
  int32_t x;
  switch (waveform_) {
  case 0:  // triangle
    x = phase_ >> 7;
    x ^= -(phase_ >> 31);
    x &= (1 << 24) - 1;
    return x;
  case 1:  // sawtooth down
    return (~phase_ ^ (1U << 31)) >> 8;
  case 2:  // sawtooth up
    return (phase_ ^ (1U << 31)) >> 8;
  case 3:  // square
    return ((~phase_) >> 7) & (1 << 24);
  case 4:  // sine
    return (1 << 23) + (Sin::lookup(phase_ >> 8) >> 1);
  case 5:  // s&h
    if (phase_ < delta_) {
      randstate_ = (randstate_ * 179 + 17) & 0xff;
    }
    x = randstate_ ^ 0x80;
    return (x + 1) << 16;
  }
  return 1 << 23;
}

int32_t Lfo::getdelay() {
  uint32_t delta = delaystate_ < (1U << 31) ? delayinc_ : delayinc2_;
  uint32_t d = delaystate_ + delta;
  if (d < delayinc_) {
    return 1 << 24;
  }
  delaystate_ = d;
  if (d < (1U << 31)) {
    return 0;
  } else {
    return (d >> 7) & ((1 << 24) - 1);
  }
}

void Lfo::keydown() {
  if (sync_) {
    phase_ = (1U << 31) - 1;
  }
  delaystate_ = 0;
}