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70 lines
1.8 KiB
70 lines
1.8 KiB
12 years ago
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/*
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* Copyright 2013 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// Low frequency oscillator, compatible with DX7
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#include "synth.h"
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#include "sin.h"
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#include "lfo.h"
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void Lfo::init(double sample_rate) {
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// constant is 1 << 32 / 15.5s / 11
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Lfo::unit_ = (int32_t)(N * 25190424 / sample_rate + 0.5);
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}
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void Lfo::reset(const char params[6]) {
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int rate = params[0]; // 0..99
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int sr = rate == 0 ? 1 : (165 * rate) >> 6;
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sr *= sr < 160 ? 11 : (11 + ((sr - 160) >> 4));
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delta_ = unit_ * sr;
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waveform_ = params[5];
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sync_ = params[4] != 0;
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}
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int32_t Lfo::getsample() {
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phase_ += delta_;
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int32_t x;
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switch (waveform_) {
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case 0: // triangle
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x = phase_ >> 7;
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x ^= -(phase_ >> 31);
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x &= (1 << 24) - 1;
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return x;
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case 1: // sawtooth down
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return (~phase_ ^ (1U << 31)) >> 8;
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case 2: // sawtooth up
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return (phase_ ^ (1U << 31)) >> 8;
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case 3: // square
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return ((~phase_) >> 7) & (1 << 24);
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case 4: // sine
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return (1 << 23) + (Sin::lookup(phase_ >> 8) >> 1);
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case 5: // s&h
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if (phase_ < delta_) {
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randstate_ = (randstate_ * 179 + 17) & 0xff;
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}
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x = randstate_ ^ 0x80;
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return (x + 1) << 16;
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}
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return 1 << 23;
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}
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void Lfo::keydown() {
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if (sync_) {
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phase_ = (1U << 31) - 1;
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}
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}
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