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53 lines
1.4 KiB
C++
53 lines
1.4 KiB
C++
//
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// KeyLevelScaler.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 02/05/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace Yamaha::OPL {
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template <int frequency_precision> class KeyLevelScaler {
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public:
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/*!
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Sets the current period associated with the channel that owns this envelope generator;
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this is used to select a key scaling rate if key-rate scaling is enabled.
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*/
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void set_period(int period, int octave) {
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constexpr int key_level_scales[16] = {0, 48, 64, 74, 80, 86, 90, 94, 96, 100, 102, 104, 106, 108, 110, 112};
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constexpr int masks[2] = {~0, 0};
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// A two's complement assumption is embedded below; the use of masks relies
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// on the sign bit to clamp to zero.
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level_ = key_level_scales[period >> (frequency_precision - 4)];
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level_ -= 16 * (octave ^ 7);
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level_ &= masks[(level_ >> ((sizeof(int) * 8) - 1)) & 1];
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}
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/*!
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Enables or disables key-rate scaling.
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*/
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void set_key_scaling_level(int level) {
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// '7' is just a number large enough to render all possible scaling coefficients as 0.
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constexpr int key_level_scale_shifts[4] = {7, 1, 2, 0};
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shift_ = key_level_scale_shifts[level];
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}
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/*!
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@returns The current attenuation level due to key-level scaling.
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*/
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int attenuation() const {
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return level_ >> shift_;
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}
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private:
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int level_ = 0;
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int shift_ = 0;
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};
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}
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