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Diffstat (limited to 'audio/softsynth/mt32/LA32WaveGenerator.h')
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diff --git a/audio/softsynth/mt32/LA32WaveGenerator.h b/audio/softsynth/mt32/LA32WaveGenerator.h new file mode 100644 index 0000000000..37a4aead85 --- /dev/null +++ b/audio/softsynth/mt32/LA32WaveGenerator.h @@ -0,0 +1,246 @@ +/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher + * Copyright (C) 2011, 2012, 2013 Dean Beeler, Jerome Fisher, Sergey V. Mikayev + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation, either version 2.1 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + +#if MT32EMU_ACCURATE_WG == 0 + +#ifndef MT32EMU_LA32_WAVE_GENERATOR_H +#define MT32EMU_LA32_WAVE_GENERATOR_H + +namespace MT32Emu { + +/** + * LA32 performs wave generation in the log-space that allows replacing multiplications by cheap additions + * It's assumed that only low-bit multiplications occur in a few places which are unavoidable like these: + * - interpolation of exponent table (obvious, a delta value has 4 bits) + * - 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) + * - interpolation of PCM samples (obvious, the wave position counter is in the linear space, there is no log() table in the chip) + * 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 + * Subtraction is supposed to be replaced by simple inversion + * As the logarithmic sine is always negative, all the logarithmic values are treated as decrements + */ +struct LogSample { + // 16-bit fixed point value, includes 12-bit fractional part + // 4-bit integer part allows to present any 16-bit sample in the log-space + // Obviously, the log value doesn't contain the sign of the resulting sample + Bit16u logValue; + enum { + POSITIVE, + NEGATIVE + } sign; +}; + +class LA32Utilites { +public: + static Bit16u interpolateExp(const Bit16u fract); + static Bit16s unlog(const LogSample &logSample); + static void addLogSamples(LogSample &logSample1, const LogSample &logSample2); +}; + +/** + * LA32WaveGenerator is aimed to represent the exact model of LA32 wave generator. + * The output square wave is created by adding high / low linear segments in-between + * the rising and falling cosine segments. Basically, it’s very similar to the phase distortion synthesis. + * Behaviour of a true resonance filter is emulated by adding decaying sine wave. + * The beginning and the ending of the resonant sine is multiplied by a cosine window. + * To synthesise sawtooth waves, the resulting square wave is multiplied by synchronous cosine wave. + */ +class LA32WaveGenerator { + //*************************************************************************** + // The local copy of partial parameters below + //*************************************************************************** + + bool active; + + // True means the resulting square wave is to be multiplied by the synchronous cosine + bool sawtoothWaveform; + + // Logarithmic amp of the wave generator + Bit32u amp; + + // Logarithmic frequency of the resulting wave + Bit16u pitch; + + // Values in range [1..31] + // Value 1 correspong to the minimum resonance + Bit8u resonance; + + // Processed value in range [0..255] + // Values in range [0..128] have no effect and the resulting wave remains symmetrical + // Value 255 corresponds to the maximum possible asymmetric of the resulting wave + Bit8u pulseWidth; + + // Composed of the base cutoff in range [78..178] left-shifted by 18 bits and the TVF modifier + Bit32u cutoffVal; + + // Logarithmic PCM sample start address + const Bit16s *pcmWaveAddress; + + // Logarithmic PCM sample length + Bit32u pcmWaveLength; + + // true for looped logarithmic PCM samples + bool pcmWaveLooped; + + // false for slave PCM partials in the structures with the ring modulation + bool pcmWaveInterpolated; + + //*************************************************************************** + // Internal variables below + //*************************************************************************** + + // Relative position within either the synth wave or the PCM sampled wave + // 0 - start of the positive rising sine segment of the square wave or start of the PCM sample + // 1048576 (2^20) - end of the negative rising sine segment of the square wave + // For PCM waves, the address of the currently playing sample equals (wavePosition / 256) + Bit32u wavePosition; + + // Relative position within a square wave phase: + // 0 - start of the phase + // 262144 (2^18) - end of a sine phase in the square wave + Bit32u squareWavePosition; + + // Relative position within the positive or negative wave segment: + // 0 - start of the corresponding positive or negative segment of the square wave + // 262144 (2^18) - corresponds to end of the first sine phase in the square wave + // The same increment sampleStep is used to indicate the current position + // since the length of the resonance wave is always equal to four square wave sine segments. + Bit32u resonanceSinePosition; + + // The amp of the resonance sine wave grows with the resonance value + // As the resonance value cannot change while the partial is active, it is initialised once + Bit32u resonanceAmpSubtraction; + + // The decay speed of resonance sine wave, depends on the resonance value + Bit32u resAmpDecayFactor; + + // Fractional part of the pcmPosition + Bit32u pcmInterpolationFactor; + + // Current phase of the square wave + enum { + POSITIVE_RISING_SINE_SEGMENT, + POSITIVE_LINEAR_SEGMENT, + POSITIVE_FALLING_SINE_SEGMENT, + NEGATIVE_FALLING_SINE_SEGMENT, + NEGATIVE_LINEAR_SEGMENT, + NEGATIVE_RISING_SINE_SEGMENT + } phase; + + // Current phase of the resonance wave + enum { + POSITIVE_RISING_RESONANCE_SINE_SEGMENT, + POSITIVE_FALLING_RESONANCE_SINE_SEGMENT, + NEGATIVE_FALLING_RESONANCE_SINE_SEGMENT, + NEGATIVE_RISING_RESONANCE_SINE_SEGMENT + } resonancePhase; + + // Resulting log-space samples of the square and resonance waves + LogSample squareLogSample; + LogSample resonanceLogSample; + + // Processed neighbour log-space samples of the PCM wave + LogSample firstPCMLogSample; + LogSample secondPCMLogSample; + + //*************************************************************************** + // Internal methods below + //*************************************************************************** + + Bit32u getSampleStep(); + Bit32u getResonanceWaveLengthFactor(Bit32u effectiveCutoffValue); + Bit32u getHighLinearLength(Bit32u effectiveCutoffValue); + + void computePositions(Bit32u highLinearLength, Bit32u lowLinearLength, Bit32u resonanceWaveLengthFactor); + void advancePosition(); + + void generateNextSquareWaveLogSample(); + void generateNextResonanceWaveLogSample(); + void generateNextSawtoothCosineLogSample(LogSample &logSample) const; + + void pcmSampleToLogSample(LogSample &logSample, const Bit16s pcmSample) const; + void generateNextPCMWaveLogSamples(); + +public: + // Initialise the WG engine for generation of synth partial samples and set up the invariant parameters + void initSynth(const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance); + + // Initialise the WG engine for generation of PCM partial samples and set up the invariant parameters + void initPCM(const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped, const bool pcmWaveInterpolated); + + // Update parameters with respect to TVP, TVA and TVF, and generate next sample + void generateNextSample(const Bit32u amp, const Bit16u pitch, const Bit32u cutoff); + + // WG output in the log-space consists of two components which are to be added (or ring modulated) in the linear-space afterwards + LogSample getOutputLogSample(const bool first) const; + + // Deactivate the WG engine + void deactivate(); + + // Return active state of the WG engine + bool isActive() const; + + // Return true if the WG engine generates PCM wave samples + bool isPCMWave() const; + + // Return current PCM interpolation factor + Bit32u getPCMInterpolationFactor() const; +}; + +// LA32PartialPair contains a structure of two partials being mixed / ring modulated +class LA32PartialPair { + LA32WaveGenerator master; + LA32WaveGenerator slave; + bool ringModulated; + bool mixed; + + static Bit16s unlogAndMixWGOutput(const LA32WaveGenerator &wg, const LogSample * const ringModulatingLogSample); + +public: + enum PairType { + MASTER, + SLAVE + }; + + // ringModulated should be set to false for the structures with mixing or stereo output + // ringModulated should be set to true for the structures with ring modulation + // mixed is used for the structures with ring modulation and indicates whether the master partial output is mixed to the ring modulator output + void init(const bool ringModulated, const bool mixed); + + // Initialise the WG engine for generation of synth partial samples and set up the invariant parameters + void initSynth(const PairType master, const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance); + + // Initialise the WG engine for generation of PCM partial samples and set up the invariant parameters + void initPCM(const PairType master, const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped); + + // Update parameters with respect to TVP, TVA and TVF, and generate next sample + void generateNextSample(const PairType master, const Bit32u amp, const Bit16u pitch, const Bit32u cutoff); + + // Perform mixing / ring modulation and return the result + Bit16s nextOutSample(); + + // Deactivate the WG engine + void deactivate(const PairType master); + + // Return active state of the WG engine + bool isActive(const PairType master) const; +}; + +} // namespace MT32Emu + +#endif // #ifndef MT32EMU_LA32_WAVE_GENERATOR_H + +#endif // #if MT32EMU_ACCURATE_WG == 0 |