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src/sound/munt/LA32WaveGenerator.h
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src/sound/munt/LA32WaveGenerator.h
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/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher
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* Copyright (C) 2011-2017 Dean Beeler, Jerome Fisher, Sergey V. Mikayev
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation, either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef MT32EMU_LA32_WAVE_GENERATOR_H
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#define MT32EMU_LA32_WAVE_GENERATOR_H
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#include "globals.h"
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#include "internals.h"
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#include "Types.h"
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namespace MT32Emu {
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/**
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* LA32 performs wave generation in the log-space that allows replacing multiplications by cheap additions
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* It's assumed that only low-bit multiplications occur in a few places which are unavoidable like these:
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* - interpolation of exponent table (obvious, a delta value has 4 bits)
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* - computation of resonance amp decay envelope (the table contains values with 1-2 "1" bits except the very first value 31 but this case can be found using inversion)
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* - interpolation of PCM samples (obvious, the wave position counter is in the linear space, there is no log() table in the chip)
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* and it seems to be implemented in the same way as in the Boss chip, i.e. right shifted additions which involved noticeable precision loss
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* Subtraction is supposed to be replaced by simple inversion
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* As the logarithmic sine is always negative, all the logarithmic values are treated as decrements
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*/
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struct LogSample {
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// 16-bit fixed point value, includes 12-bit fractional part
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// 4-bit integer part allows to present any 16-bit sample in the log-space
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// Obviously, the log value doesn't contain the sign of the resulting sample
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Bit16u logValue;
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enum {
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POSITIVE,
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NEGATIVE
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} sign;
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};
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class LA32Utilites {
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public:
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static Bit16u interpolateExp(const Bit16u fract);
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static Bit16s unlog(const LogSample &logSample);
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static void addLogSamples(LogSample &logSample1, const LogSample &logSample2);
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};
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/**
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* LA32WaveGenerator is aimed to represent the exact model of LA32 wave generator.
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* The output square wave is created by adding high / low linear segments in-between
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* the rising and falling cosine segments. Basically, it's very similar to the phase distortion synthesis.
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* Behaviour of a true resonance filter is emulated by adding decaying sine wave.
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* The beginning and the ending of the resonant sine is multiplied by a cosine window.
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* To synthesise sawtooth waves, the resulting square wave is multiplied by synchronous cosine wave.
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*/
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class LA32WaveGenerator {
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//***************************************************************************
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// The local copy of partial parameters below
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//***************************************************************************
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bool active;
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// True means the resulting square wave is to be multiplied by the synchronous cosine
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bool sawtoothWaveform;
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// Logarithmic amp of the wave generator
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Bit32u amp;
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// Logarithmic frequency of the resulting wave
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Bit16u pitch;
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// Values in range [1..31]
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// Value 1 correspong to the minimum resonance
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Bit8u resonance;
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// Processed value in range [0..255]
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// Values in range [0..128] have no effect and the resulting wave remains symmetrical
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// Value 255 corresponds to the maximum possible asymmetric of the resulting wave
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Bit8u pulseWidth;
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// Composed of the base cutoff in range [78..178] left-shifted by 18 bits and the TVF modifier
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Bit32u cutoffVal;
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// Logarithmic PCM sample start address
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const Bit16s *pcmWaveAddress;
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// Logarithmic PCM sample length
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Bit32u pcmWaveLength;
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// true for looped logarithmic PCM samples
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bool pcmWaveLooped;
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// false for slave PCM partials in the structures with the ring modulation
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bool pcmWaveInterpolated;
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//***************************************************************************
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// Internal variables below
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//***************************************************************************
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// Relative position within either the synth wave or the PCM sampled wave
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// 0 - start of the positive rising sine segment of the square wave or start of the PCM sample
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// 1048576 (2^20) - end of the negative rising sine segment of the square wave
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// For PCM waves, the address of the currently playing sample equals (wavePosition / 256)
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Bit32u wavePosition;
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// Relative position within a square wave phase:
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// 0 - start of the phase
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// 262144 (2^18) - end of a sine phase in the square wave
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Bit32u squareWavePosition;
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// Relative position within the positive or negative wave segment:
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// 0 - start of the corresponding positive or negative segment of the square wave
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// 262144 (2^18) - corresponds to end of the first sine phase in the square wave
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// The same increment sampleStep is used to indicate the current position
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// since the length of the resonance wave is always equal to four square wave sine segments.
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Bit32u resonanceSinePosition;
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// The amp of the resonance sine wave grows with the resonance value
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// As the resonance value cannot change while the partial is active, it is initialised once
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Bit32u resonanceAmpSubtraction;
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// The decay speed of resonance sine wave, depends on the resonance value
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Bit32u resAmpDecayFactor;
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// Fractional part of the pcmPosition
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Bit32u pcmInterpolationFactor;
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// Current phase of the square wave
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enum {
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POSITIVE_RISING_SINE_SEGMENT,
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POSITIVE_LINEAR_SEGMENT,
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POSITIVE_FALLING_SINE_SEGMENT,
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NEGATIVE_FALLING_SINE_SEGMENT,
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NEGATIVE_LINEAR_SEGMENT,
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NEGATIVE_RISING_SINE_SEGMENT
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} phase;
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// Current phase of the resonance wave
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enum ResonancePhase {
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POSITIVE_RISING_RESONANCE_SINE_SEGMENT,
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POSITIVE_FALLING_RESONANCE_SINE_SEGMENT,
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NEGATIVE_FALLING_RESONANCE_SINE_SEGMENT,
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NEGATIVE_RISING_RESONANCE_SINE_SEGMENT
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} resonancePhase;
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// Resulting log-space samples of the square and resonance waves
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LogSample squareLogSample;
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LogSample resonanceLogSample;
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// Processed neighbour log-space samples of the PCM wave
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LogSample firstPCMLogSample;
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LogSample secondPCMLogSample;
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//***************************************************************************
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// Internal methods below
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//***************************************************************************
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Bit32u getSampleStep();
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Bit32u getResonanceWaveLengthFactor(Bit32u effectiveCutoffValue);
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Bit32u getHighLinearLength(Bit32u effectiveCutoffValue);
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void computePositions(Bit32u highLinearLength, Bit32u lowLinearLength, Bit32u resonanceWaveLengthFactor);
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void advancePosition();
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void generateNextSquareWaveLogSample();
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void generateNextResonanceWaveLogSample();
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void generateNextSawtoothCosineLogSample(LogSample &logSample) const;
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void pcmSampleToLogSample(LogSample &logSample, const Bit16s pcmSample) const;
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void generateNextPCMWaveLogSamples();
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public:
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// Initialise the WG engine for generation of synth partial samples and set up the invariant parameters
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void initSynth(const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance);
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// Initialise the WG engine for generation of PCM partial samples and set up the invariant parameters
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void initPCM(const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped, const bool pcmWaveInterpolated);
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// Update parameters with respect to TVP, TVA and TVF, and generate next sample
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void generateNextSample(const Bit32u amp, const Bit16u pitch, const Bit32u cutoff);
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// WG output in the log-space consists of two components which are to be added (or ring modulated) in the linear-space afterwards
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LogSample getOutputLogSample(const bool first) const;
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// Deactivate the WG engine
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void deactivate();
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// Return active state of the WG engine
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bool isActive() const;
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// Return true if the WG engine generates PCM wave samples
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bool isPCMWave() const;
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// Return current PCM interpolation factor
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Bit32u getPCMInterpolationFactor() const;
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}; // class LA32WaveGenerator
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// LA32PartialPair contains a structure of two partials being mixed / ring modulated
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class LA32PartialPair {
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public:
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enum PairType {
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MASTER,
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SLAVE
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};
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virtual ~LA32PartialPair() {}
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// ringModulated should be set to false for the structures with mixing or stereo output
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// ringModulated should be set to true for the structures with ring modulation
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// mixed is used for the structures with ring modulation and indicates whether the master partial output is mixed to the ring modulator output
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virtual void init(const bool ringModulated, const bool mixed) = 0;
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// Initialise the WG engine for generation of synth partial samples and set up the invariant parameters
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virtual void initSynth(const PairType master, const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance) = 0;
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// Initialise the WG engine for generation of PCM partial samples and set up the invariant parameters
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virtual void initPCM(const PairType master, const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped) = 0;
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// Deactivate the WG engine
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virtual void deactivate(const PairType master) = 0;
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}; // class LA32PartialPair
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class LA32IntPartialPair : public LA32PartialPair {
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LA32WaveGenerator master;
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LA32WaveGenerator slave;
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bool ringModulated;
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bool mixed;
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static Bit16s unlogAndMixWGOutput(const LA32WaveGenerator &wg);
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public:
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// ringModulated should be set to false for the structures with mixing or stereo output
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// ringModulated should be set to true for the structures with ring modulation
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// mixed is used for the structures with ring modulation and indicates whether the master partial output is mixed to the ring modulator output
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void init(const bool ringModulated, const bool mixed);
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// Initialise the WG engine for generation of synth partial samples and set up the invariant parameters
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void initSynth(const PairType master, const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance);
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// Initialise the WG engine for generation of PCM partial samples and set up the invariant parameters
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void initPCM(const PairType master, const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped);
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// Update parameters with respect to TVP, TVA and TVF, and generate next sample
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void generateNextSample(const PairType master, const Bit32u amp, const Bit16u pitch, const Bit32u cutoff);
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// Perform mixing / ring modulation of WG output and return the result
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// Although, LA32 applies panning itself, we assume it is applied in the mixer, not within a pair
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Bit16s nextOutSample();
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// Deactivate the WG engine
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void deactivate(const PairType master);
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// Return active state of the WG engine
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bool isActive(const PairType master) const;
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}; // class LA32IntPartialPair
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} // namespace MT32Emu
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#endif // #ifndef MT32EMU_LA32_WAVE_GENERATOR_H
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