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126 lines
3.4 KiB
C++
126 lines
3.4 KiB
C++
//
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// PhaseGenerator.h
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// Clock Signal
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//
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// Created by Thomas Harte on 30/04/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#ifndef PhaseGenerator_h
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#define PhaseGenerator_h
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#include <cassert>
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#include "LowFrequencyOscillator.hpp"
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#include "Tables.hpp"
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namespace Yamaha {
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namespace OPL {
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/*!
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Models an OPL-style phase generator of templated precision; having been told its period ('f-num'), octave ('block') and
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multiple, and whether to apply vibrato, this will then appropriately update and return phase.
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*/
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template <int precision> class PhaseGenerator {
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public:
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/*!
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Advances the phase generator a single step, given the current state of the low-frequency oscillator, @c oscillator.
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*/
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void update(const LowFrequencyOscillator &oscillator) {
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constexpr int vibrato_shifts[4] = {3, 1, 0, 1};
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constexpr int vibrato_signs[2] = {1, -1};
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// Get just the top three bits of the period_.
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const int top_freq = period_ >> (precision - 3);
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// Cacluaute applicable vibrato as a function of (i) the top three bits of the
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// oscillator period; (ii) the current low-frequency oscillator vibrato output; and
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// (iii) whether vibrato is enabled.
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const int vibrato = (top_freq >> vibrato_shifts[oscillator.vibrato & 3]) * vibrato_signs[oscillator.vibrato >> 2] * enable_vibrato_;
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// Apply phase update with vibrato from the low-frequency oscillator.
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phase_ += (multiple_ * ((period_ << 1) + vibrato) << octave_) >> 1;
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}
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/*!
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@returns Current phase; real hardware provides only the low ten bits of this result.
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*/
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int phase() const {
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// My table if multipliers is multiplied by two, so shift by one more
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// than the stated precision.
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return phase_ >> precision_shift;
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}
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/*!
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@returns Current phase, scaled up by (1 << precision).
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*/
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int scaled_phase() const {
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return phase_ >> 1;
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}
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/*!
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Applies feedback based on two historic samples of a total output level,
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plus the degree of feedback to apply
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*/
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void apply_feedback(LogSign first, LogSign second, int level) {
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constexpr int masks[] = {0, ~0, ~0, ~0, ~0, ~0, ~0, ~0};
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phase_ += ((second.level(precision) + first.level(precision)) >> (8 - level)) & masks[level];
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}
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/*!
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Sets the multiple for this phase generator, in the same terms as an OPL programmer,
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i.e. a 4-bit number that is used as a lookup into the internal multiples table.
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*/
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void set_multiple(int multiple) {
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// This encodes the MUL -> multiple table given on page 12,
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// multiplied by two.
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constexpr int multipliers[] = {
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1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 20, 24, 24, 30, 30
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};
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assert(multiple < 16);
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multiple_ = multipliers[multiple];
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}
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/*!
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Sets the period of this generator, along with its current octave.
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Yamaha tends to refer to the period as the 'f-number', and used both 'octave' and 'block' for octave.
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*/
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void set_period(int period, int octave) {
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period_ = period;
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octave_ = octave;
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assert(octave_ < 8);
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assert(period_ < (1 << precision));
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}
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/*!
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Enables or disables vibrato.
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*/
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void set_vibrato_enabled(bool enabled) {
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enable_vibrato_ = int(enabled);
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}
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/*!
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Resets the current phase.
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*/
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void reset() {
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phase_ = 0;
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}
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private:
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static constexpr int precision_shift = 1 + precision;
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int phase_ = 0;
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int multiple_ = 0;
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int period_ = 0;
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int octave_ = 0;
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int enable_vibrato_ = 0;
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};
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}
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}
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#endif /* PhaseGenerator_h */
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