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52 lines
1.4 KiB
C++
52 lines
1.4 KiB
C++
//
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// LowFrequencyOscillator.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 23/04/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#ifndef LowFrequencyOscillator_hpp
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#define LowFrequencyOscillator_hpp
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#include "../../../Numeric/LFSR.hpp"
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namespace Yamaha {
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namespace OPL {
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/*!
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Models the output of the OPL low-frequency oscillator, which provides a couple of optional fixed-frequency
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modifications to an operator: tremolo and vibrato. Also exposes a global time counter, which oscillators use
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as part of their ADSR envelope.
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*/
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class LowFrequencyOscillator {
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public:
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/// Current attenuation due to tremolo / amplitude modulation, between 0 and 26.
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int tremolo = 0;
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/// A number between 0 and 7 indicating the current vibrato offset; this should be combined by operators
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/// with their frequency number to get the actual vibrato.
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int vibrato = 0;
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/// A counter of the number of operator update cycles (i.e. input clock / 72) since an arbitrary time.
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int counter = 0;
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/// Describes the current output of the LFSR; will be either 0 or 1.
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int lfsr = 0;
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/// Updates the oscillator outputs. Should be called at the (input clock/72) rate.
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void update();
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/// Updartes the LFSR output. Should be called at the input clock rate.
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void update_lfsr();
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private:
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// This is the correct LSFR per forums.submarine.org.uk.
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Numeric::LFSR<int, 0x800302> noise_source_;
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};
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}
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}
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#endif /* LowFrequencyOscillator_hpp */
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