aboutsummaryrefslogtreecommitdiff
path: root/audio/softsynth/mt32/LA32WaveGenerator.cpp
blob: f6f6928801f53b71317a5fce24f7a2c329f307d8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
/* Copyright (C) 2003, 2004, 2005, 2006, 2008, 2009 Dean Beeler, Jerome Fisher
 * Copyright (C) 2011-2017 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/>.
 */

#include <cstddef>

#include "internals.h"

#include "LA32WaveGenerator.h"
#include "Tables.h"

namespace MT32Emu {

static const Bit32u SINE_SEGMENT_RELATIVE_LENGTH = 1 << 18;
static const Bit32u MIDDLE_CUTOFF_VALUE = 128 << 18;
static const Bit32u RESONANCE_DECAY_THRESHOLD_CUTOFF_VALUE = 144 << 18;
static const Bit32u MAX_CUTOFF_VALUE = 240 << 18;
static const LogSample SILENCE = {65535, LogSample::POSITIVE};

Bit16u LA32Utilites::interpolateExp(const Bit16u fract) {
	Bit16u expTabIndex = fract >> 3;
	Bit16u extraBits = ~fract & 7;
	Bit16u expTabEntry2 = 8191 - Tables::getInstance().exp9[expTabIndex];
	Bit16u expTabEntry1 = expTabIndex == 0 ? 8191 : (8191 - Tables::getInstance().exp9[expTabIndex - 1]);
	return expTabEntry2 + (((expTabEntry1 - expTabEntry2) * extraBits) >> 3);
}

Bit16s LA32Utilites::unlog(const LogSample &logSample) {
	//Bit16s sample = (Bit16s)EXP2F(13.0f - logSample.logValue / 1024.0f);
	Bit32u intLogValue = logSample.logValue >> 12;
	Bit16u fracLogValue = logSample.logValue & 4095;
	Bit16s sample = interpolateExp(fracLogValue) >> intLogValue;
	return logSample.sign == LogSample::POSITIVE ? sample : -sample;
}

void LA32Utilites::addLogSamples(LogSample &logSample1, const LogSample &logSample2) {
	Bit32u logSampleValue = logSample1.logValue + logSample2.logValue;
	logSample1.logValue = logSampleValue < 65536 ? Bit16u(logSampleValue) : 65535;
	logSample1.sign = logSample1.sign == logSample2.sign ? LogSample::POSITIVE : LogSample::NEGATIVE;
}

Bit32u LA32WaveGenerator::getSampleStep() {
	// sampleStep = EXP2F(pitch / 4096.0f + 4.0f)
	Bit32u sampleStep = LA32Utilites::interpolateExp(~pitch & 4095);
	sampleStep <<= pitch >> 12;
	sampleStep >>= 8;
	sampleStep &= ~1;
	return sampleStep;
}

Bit32u LA32WaveGenerator::getResonanceWaveLengthFactor(Bit32u effectiveCutoffValue) {
	// resonanceWaveLengthFactor = (Bit32u)EXP2F(12.0f + effectiveCutoffValue / 4096.0f);
	Bit32u resonanceWaveLengthFactor = LA32Utilites::interpolateExp(~effectiveCutoffValue & 4095);
	resonanceWaveLengthFactor <<= effectiveCutoffValue >> 12;
	return resonanceWaveLengthFactor;
}

Bit32u LA32WaveGenerator::getHighLinearLength(Bit32u effectiveCutoffValue) {
	// Ratio of positive segment to wave length
	Bit32u effectivePulseWidthValue = 0;
	if (pulseWidth > 128) {
		effectivePulseWidthValue = (pulseWidth - 128) << 6;
	}

	Bit32u highLinearLength = 0;
	// highLinearLength = EXP2F(19.0f - effectivePulseWidthValue / 4096.0f + effectiveCutoffValue / 4096.0f) - 2 * SINE_SEGMENT_RELATIVE_LENGTH;
	if (effectivePulseWidthValue < effectiveCutoffValue) {
		Bit32u expArg = effectiveCutoffValue - effectivePulseWidthValue;
		highLinearLength = LA32Utilites::interpolateExp(~expArg & 4095);
		highLinearLength <<= 7 + (expArg >> 12);
		highLinearLength -= 2 * SINE_SEGMENT_RELATIVE_LENGTH;
	}
	return highLinearLength;
}

void LA32WaveGenerator::computePositions(Bit32u highLinearLength, Bit32u lowLinearLength, Bit32u resonanceWaveLengthFactor) {
	// Assuming 12-bit multiplication used here
	squareWavePosition = resonanceSinePosition = (wavePosition >> 8) * (resonanceWaveLengthFactor >> 4);
	if (squareWavePosition < SINE_SEGMENT_RELATIVE_LENGTH) {
		phase = POSITIVE_RISING_SINE_SEGMENT;
		return;
	}
	squareWavePosition -= SINE_SEGMENT_RELATIVE_LENGTH;
	if (squareWavePosition < highLinearLength) {
		phase = POSITIVE_LINEAR_SEGMENT;
		return;
	}
	squareWavePosition -= highLinearLength;
	if (squareWavePosition < SINE_SEGMENT_RELATIVE_LENGTH) {
		phase = POSITIVE_FALLING_SINE_SEGMENT;
		return;
	}
	squareWavePosition -= SINE_SEGMENT_RELATIVE_LENGTH;
	resonanceSinePosition = squareWavePosition;
	if (squareWavePosition < SINE_SEGMENT_RELATIVE_LENGTH) {
		phase = NEGATIVE_FALLING_SINE_SEGMENT;
		return;
	}
	squareWavePosition -= SINE_SEGMENT_RELATIVE_LENGTH;
	if (squareWavePosition < lowLinearLength) {
		phase = NEGATIVE_LINEAR_SEGMENT;
		return;
	}
	squareWavePosition -= lowLinearLength;
	phase = NEGATIVE_RISING_SINE_SEGMENT;
}

void LA32WaveGenerator::advancePosition() {
	wavePosition += getSampleStep();
	wavePosition %= 4 * SINE_SEGMENT_RELATIVE_LENGTH;

	Bit32u effectiveCutoffValue = (cutoffVal > MIDDLE_CUTOFF_VALUE) ? (cutoffVal - MIDDLE_CUTOFF_VALUE) >> 10 : 0;
	Bit32u resonanceWaveLengthFactor = getResonanceWaveLengthFactor(effectiveCutoffValue);
	Bit32u highLinearLength = getHighLinearLength(effectiveCutoffValue);
	Bit32u lowLinearLength = (resonanceWaveLengthFactor << 8) - 4 * SINE_SEGMENT_RELATIVE_LENGTH - highLinearLength;
	computePositions(highLinearLength, lowLinearLength, resonanceWaveLengthFactor);

	resonancePhase = ResonancePhase(((resonanceSinePosition >> 18) + (phase > POSITIVE_FALLING_SINE_SEGMENT ? 2 : 0)) & 3);
}

void LA32WaveGenerator::generateNextSquareWaveLogSample() {
	Bit32u logSampleValue;
	switch (phase) {
		case POSITIVE_RISING_SINE_SEGMENT:
		case NEGATIVE_FALLING_SINE_SEGMENT:
			logSampleValue = Tables::getInstance().logsin9[(squareWavePosition >> 9) & 511];
			break;
		case POSITIVE_FALLING_SINE_SEGMENT:
		case NEGATIVE_RISING_SINE_SEGMENT:
			logSampleValue = Tables::getInstance().logsin9[~(squareWavePosition >> 9) & 511];
			break;
		case POSITIVE_LINEAR_SEGMENT:
		case NEGATIVE_LINEAR_SEGMENT:
		default:
			logSampleValue = 0;
			break;
	}
	logSampleValue <<= 2;
	logSampleValue += amp >> 10;
	if (cutoffVal < MIDDLE_CUTOFF_VALUE) {
		logSampleValue += (MIDDLE_CUTOFF_VALUE - cutoffVal) >> 9;
	}

	squareLogSample.logValue = logSampleValue < 65536 ? Bit16u(logSampleValue) : 65535;
	squareLogSample.sign = phase < NEGATIVE_FALLING_SINE_SEGMENT ? LogSample::POSITIVE : LogSample::NEGATIVE;
}

void LA32WaveGenerator::generateNextResonanceWaveLogSample() {
	Bit32u logSampleValue;
	if (resonancePhase == POSITIVE_FALLING_RESONANCE_SINE_SEGMENT || resonancePhase == NEGATIVE_RISING_RESONANCE_SINE_SEGMENT) {
		logSampleValue = Tables::getInstance().logsin9[~(resonanceSinePosition >> 9) & 511];
	} else {
		logSampleValue = Tables::getInstance().logsin9[(resonanceSinePosition >> 9) & 511];
	}
	logSampleValue <<= 2;
	logSampleValue += amp >> 10;

	// From the digital captures, the decaying speed of the resonance sine is found a bit different for the positive and the negative segments
	Bit32u decayFactor = phase < NEGATIVE_FALLING_SINE_SEGMENT ? resAmpDecayFactor : resAmpDecayFactor + 1;
	// Unsure about resonanceSinePosition here. It's possible that dedicated counter & decrement are used. Although, cutoff is finely ramped, so maybe not.
	logSampleValue += resonanceAmpSubtraction + (((resonanceSinePosition >> 4) * decayFactor) >> 8);

	// To ensure the output wave has no breaks, two different windows are appied to the beginning and the ending of the resonance sine segment
	if (phase == POSITIVE_RISING_SINE_SEGMENT || phase == NEGATIVE_FALLING_SINE_SEGMENT) {
		// The window is synchronous sine here
		logSampleValue += Tables::getInstance().logsin9[(squareWavePosition >> 9) & 511] << 2;
	} else if (phase == POSITIVE_FALLING_SINE_SEGMENT || phase == NEGATIVE_RISING_SINE_SEGMENT) {
		// The window is synchronous square sine here
		logSampleValue += Tables::getInstance().logsin9[~(squareWavePosition >> 9) & 511] << 3;
	}

	if (cutoffVal < MIDDLE_CUTOFF_VALUE) {
		// For the cutoff values below the cutoff middle point, it seems the amp of the resonance wave is expotentially decayed
		logSampleValue += 31743 + ((MIDDLE_CUTOFF_VALUE - cutoffVal) >> 9);
	} else if (cutoffVal < RESONANCE_DECAY_THRESHOLD_CUTOFF_VALUE) {
		// For the cutoff values below this point, the amp of the resonance wave is sinusoidally decayed
		Bit32u sineIx = (cutoffVal - MIDDLE_CUTOFF_VALUE) >> 13;
		logSampleValue += Tables::getInstance().logsin9[sineIx] << 2;
	}

	// After all the amp decrements are added, it should be safe now to adjust the amp of the resonance wave to what we see on captures
	logSampleValue -= 1 << 12;

	resonanceLogSample.logValue = logSampleValue < 65536 ? Bit16u(logSampleValue) : 65535;
	resonanceLogSample.sign = resonancePhase < NEGATIVE_FALLING_RESONANCE_SINE_SEGMENT ? LogSample::POSITIVE : LogSample::NEGATIVE;
}

void LA32WaveGenerator::generateNextSawtoothCosineLogSample(LogSample &logSample) const {
	Bit32u sawtoothCosinePosition = wavePosition + (1 << 18);
	if ((sawtoothCosinePosition & (1 << 18)) > 0) {
		logSample.logValue = Tables::getInstance().logsin9[~(sawtoothCosinePosition >> 9) & 511];
	} else {
		logSample.logValue = Tables::getInstance().logsin9[(sawtoothCosinePosition >> 9) & 511];
	}
	logSample.logValue <<= 2;
	logSample.sign = ((sawtoothCosinePosition & (1 << 19)) == 0) ? LogSample::POSITIVE : LogSample::NEGATIVE;
}

void LA32WaveGenerator::pcmSampleToLogSample(LogSample &logSample, const Bit16s pcmSample) const {
	Bit32u logSampleValue = (32787 - (pcmSample & 32767)) << 1;
	logSampleValue += amp >> 10;
	logSample.logValue = logSampleValue < 65536 ? Bit16u(logSampleValue) : 65535;
	logSample.sign = pcmSample < 0 ? LogSample::NEGATIVE : LogSample::POSITIVE;
}

void LA32WaveGenerator::generateNextPCMWaveLogSamples() {
	// This should emulate the ladder we see in the PCM captures for pitches 01, 02, 07, etc.
	// The most probable cause is the factor in the interpolation formula is one bit less
	// accurate than the sample position counter
	pcmInterpolationFactor = (wavePosition & 255) >> 1;
	Bit32u pcmWaveTableIx = wavePosition >> 8;
	pcmSampleToLogSample(firstPCMLogSample, pcmWaveAddress[pcmWaveTableIx]);
	if (pcmWaveInterpolated) {
		pcmWaveTableIx++;
		if (pcmWaveTableIx < pcmWaveLength) {
			pcmSampleToLogSample(secondPCMLogSample, pcmWaveAddress[pcmWaveTableIx]);
		} else {
			if (pcmWaveLooped) {
				pcmWaveTableIx -= pcmWaveLength;
				pcmSampleToLogSample(secondPCMLogSample, pcmWaveAddress[pcmWaveTableIx]);
			} else {
				secondPCMLogSample = SILENCE;
			}
		}
	} else {
		secondPCMLogSample = SILENCE;
	}
	// pcmSampleStep = (Bit32u)EXP2F(pitch / 4096.0f + 3.0f);
	Bit32u pcmSampleStep = LA32Utilites::interpolateExp(~pitch & 4095);
	pcmSampleStep <<= pitch >> 12;
	// Seeing the actual lengths of the PCM wave for pitches 00..12,
	// the pcmPosition counter can be assumed to have 8-bit fractions
	pcmSampleStep >>= 9;
	wavePosition += pcmSampleStep;
	if (wavePosition >= (pcmWaveLength << 8)) {
		if (pcmWaveLooped) {
			wavePosition -= pcmWaveLength << 8;
		} else {
			deactivate();
		}
	}
}

void LA32WaveGenerator::initSynth(const bool useSawtoothWaveform, const Bit8u usePulseWidth, const Bit8u useResonance) {
	sawtoothWaveform = useSawtoothWaveform;
	pulseWidth = usePulseWidth;
	resonance = useResonance;

	wavePosition = 0;

	squareWavePosition = 0;
	phase = POSITIVE_RISING_SINE_SEGMENT;

	resonanceSinePosition = 0;
	resonancePhase = POSITIVE_RISING_RESONANCE_SINE_SEGMENT;
	resonanceAmpSubtraction = (32 - resonance) << 10;
	resAmpDecayFactor = Tables::getInstance().resAmpDecayFactor[resonance >> 2] << 2;

	pcmWaveAddress = NULL;
	active = true;
}

void LA32WaveGenerator::initPCM(const Bit16s * const usePCMWaveAddress, const Bit32u usePCMWaveLength, const bool usePCMWaveLooped, const bool usePCMWaveInterpolated) {
	pcmWaveAddress = usePCMWaveAddress;
	pcmWaveLength = usePCMWaveLength;
	pcmWaveLooped = usePCMWaveLooped;
	pcmWaveInterpolated = usePCMWaveInterpolated;

	wavePosition = 0;
	active = true;
}

void LA32WaveGenerator::generateNextSample(const Bit32u useAmp, const Bit16u usePitch, const Bit32u useCutoffVal) {
	if (!active) {
		return;
	}

	amp = useAmp;
	pitch = usePitch;

	if (isPCMWave()) {
		generateNextPCMWaveLogSamples();
		return;
	}

	// The 240 cutoffVal limit was determined via sample analysis (internal Munt capture IDs: glop3, glop4).
	// More research is needed to be sure that this is correct, however.
	cutoffVal = (useCutoffVal > MAX_CUTOFF_VALUE) ? MAX_CUTOFF_VALUE : useCutoffVal;

	generateNextSquareWaveLogSample();
	generateNextResonanceWaveLogSample();
	if (sawtoothWaveform) {
		LogSample cosineLogSample;
		generateNextSawtoothCosineLogSample(cosineLogSample);
		LA32Utilites::addLogSamples(squareLogSample, cosineLogSample);
		LA32Utilites::addLogSamples(resonanceLogSample, cosineLogSample);
	}
	advancePosition();
}

LogSample LA32WaveGenerator::getOutputLogSample(const bool first) const {
	if (!isActive()) {
		return SILENCE;
	}
	if (isPCMWave()) {
		return first ? firstPCMLogSample : secondPCMLogSample;
	}
	return first ? squareLogSample : resonanceLogSample;
}

void LA32WaveGenerator::deactivate() {
	active = false;
}

bool LA32WaveGenerator::isActive() const {
	return active;
}

bool LA32WaveGenerator::isPCMWave() const {
	return pcmWaveAddress != NULL;
}

Bit32u LA32WaveGenerator::getPCMInterpolationFactor() const {
	return pcmInterpolationFactor;
}

void LA32IntPartialPair::init(const bool useRingModulated, const bool useMixed) {
	ringModulated = useRingModulated;
	mixed = useMixed;
}

void LA32IntPartialPair::initSynth(const PairType useMaster, const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance) {
	if (useMaster == MASTER) {
		master.initSynth(sawtoothWaveform, pulseWidth, resonance);
	} else {
		slave.initSynth(sawtoothWaveform, pulseWidth, resonance);
	}
}

void LA32IntPartialPair::initPCM(const PairType useMaster, const Bit16s *pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped) {
	if (useMaster == MASTER) {
		master.initPCM(pcmWaveAddress, pcmWaveLength, pcmWaveLooped, true);
	} else {
		slave.initPCM(pcmWaveAddress, pcmWaveLength, pcmWaveLooped, !ringModulated);
	}
}

void LA32IntPartialPair::generateNextSample(const PairType useMaster, const Bit32u amp, const Bit16u pitch, const Bit32u cutoff) {
	if (useMaster == MASTER) {
		master.generateNextSample(amp, pitch, cutoff);
	} else {
		slave.generateNextSample(amp, pitch, cutoff);
	}
}

Bit16s LA32IntPartialPair::unlogAndMixWGOutput(const LA32WaveGenerator &wg) {
	if (!wg.isActive()) {
		return 0;
	}
	Bit16s firstSample = LA32Utilites::unlog(wg.getOutputLogSample(true));
	Bit16s secondSample = LA32Utilites::unlog(wg.getOutputLogSample(false));
	if (wg.isPCMWave()) {
		return Bit16s(firstSample + (((Bit32s(secondSample) - Bit32s(firstSample)) * wg.getPCMInterpolationFactor()) >> 7));
	}
	return firstSample + secondSample;
}

static inline Bit16s produceDistortedSample(Bit16s sample) {
	return ((sample & 0x2000) == 0) ? Bit16s(sample & 0x1fff) : Bit16s(sample | ~0x1fff);
}

Bit16s LA32IntPartialPair::nextOutSample() {
	if (!ringModulated) {
		return unlogAndMixWGOutput(master) + unlogAndMixWGOutput(slave);
	}

	Bit16s masterSample = unlogAndMixWGOutput(master); // Store master partial sample for further mixing

	/* SEMI-CONFIRMED from sample analysis:
	 * We observe that for partial structures with ring modulation the interpolation is not applied to the slave PCM partial.
	 * It's assumed that the multiplication circuitry intended to perform the interpolation on the slave PCM partial
	 * is borrowed by the ring modulation circuit (or the LA32 chip has a similar lack of resources assigned to each partial pair).
	 */
	Bit16s slaveSample = slave.isPCMWave() ? LA32Utilites::unlog(slave.getOutputLogSample(true)) : unlogAndMixWGOutput(slave);

	/* SEMI-CONFIRMED: Ring modulation model derived from sample analysis of specially constructed patches which exploit distortion.
	 * LA32 ring modulator found to produce distorted output in case if the absolute value of maximal amplitude of one of the input partials exceeds 8191.
	 * This is easy to reproduce using synth partials with resonance values close to the maximum. It looks like an integer overflow happens in this case.
	 * As the distortion is strictly bound to the amplitude of the complete mixed square + resonance wave in the linear space,
	 * it is reasonable to assume the ring modulation is performed also in the linear space by sample multiplication.
	 * Most probably the overflow is caused by limited precision of the multiplication circuit as the very similar distortion occurs with panning.
	 */
	Bit16s ringModulatedSample = Bit16s((Bit32s(produceDistortedSample(masterSample)) * Bit32s(produceDistortedSample(slaveSample))) >> 13);

	return mixed ? masterSample + ringModulatedSample : ringModulatedSample;
}

void LA32IntPartialPair::deactivate(const PairType useMaster) {
	if (useMaster == MASTER) {
		master.deactivate();
	} else {
		slave.deactivate();
	}
}

bool LA32IntPartialPair::isActive(const PairType useMaster) const {
	return useMaster == MASTER ? master.isActive() : slave.isActive();
}

} // namespace MT32Emu