aboutsummaryrefslogtreecommitdiff
path: root/audio/softsynth/mt32/LegacyWaveGenerator.cpp
blob: 35ca9750189c85a557862a307fcf0e6e94dfa6ce (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
/* 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/>.
 */

//#include <cmath>
#include "mt32emu.h"
#include "mmath.h"
#include "LegacyWaveGenerator.h"

#if MT32EMU_ACCURATE_WG == 1

namespace MT32Emu {

static const float MIDDLE_CUTOFF_VALUE = 128.0f;
static const float RESONANCE_DECAY_THRESHOLD_CUTOFF_VALUE = 144.0f;
static const float MAX_CUTOFF_VALUE = 240.0f;

float LA32WaveGenerator::getPCMSample(unsigned int position) {
	if (position >= pcmWaveLength) {
		if (!pcmWaveLooped) {
			return 0;
		}
		position = position % pcmWaveLength;
	}
	Bit16s pcmSample = pcmWaveAddress[position];
	float sampleValue = EXP2F(((pcmSample & 32767) - 32787.0f) / 2048.0f);
	return ((pcmSample & 32768) == 0) ? sampleValue : -sampleValue;
}

void LA32WaveGenerator::initSynth(const bool sawtoothWaveform, const Bit8u pulseWidth, const Bit8u resonance) {
	this->sawtoothWaveform = sawtoothWaveform;
	this->pulseWidth = pulseWidth;
	this->resonance = resonance;

	wavePos = 0.0f;
	lastFreq = 0.0f;

	pcmWaveAddress = NULL;
	active = true;
}

void LA32WaveGenerator::initPCM(const Bit16s * const pcmWaveAddress, const Bit32u pcmWaveLength, const bool pcmWaveLooped, const bool pcmWaveInterpolated) {
	this->pcmWaveAddress = pcmWaveAddress;
	this->pcmWaveLength = pcmWaveLength;
	this->pcmWaveLooped = pcmWaveLooped;
	this->pcmWaveInterpolated = pcmWaveInterpolated;

	pcmPosition = 0.0f;
	active = true;
}

float LA32WaveGenerator::generateNextSample(const Bit32u ampVal, const Bit16u pitch, const Bit32u cutoffRampVal) {
	if (!active) {
		return 0.0f;
	}

	this->amp = amp;
	this->pitch = pitch;

	float sample = 0.0f;

	// SEMI-CONFIRMED: From sample analysis:
	// (1) Tested with a single partial playing PCM wave 77 with pitchCoarse 36 and no keyfollow, velocity follow, etc.
	// This gives results within +/- 2 at the output (before any DAC bitshifting)
	// when sustaining at levels 156 - 255 with no modifiers.
	// (2) Tested with a special square wave partial (internal capture ID tva5) at TVA envelope levels 155-255.
	// This gives deltas between -1 and 0 compared to the real output. Note that this special partial only produces
	// positive amps, so negative still needs to be explored, as well as lower levels.
	//
	// Also still partially unconfirmed is the behaviour when ramping between levels, as well as the timing.

	float amp = EXP2F(ampVal / -1024.0f / 4096.0f);
	float freq = EXP2F(pitch / 4096.0f - 16.0f) * SAMPLE_RATE;

	if (isPCMWave()) {
		// Render PCM waveform
		int len = pcmWaveLength;
		int intPCMPosition = (int)pcmPosition;
		if (intPCMPosition >= len && !pcmWaveLooped) {
			// We're now past the end of a non-looping PCM waveform so it's time to die.
			deactivate();
			return 0.0f;
		}
		float positionDelta = freq * 2048.0f / SAMPLE_RATE;

		// Linear interpolation
		float firstSample = getPCMSample(intPCMPosition);
		// 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).
		if (pcmWaveInterpolated) {
			sample = firstSample + (getPCMSample(intPCMPosition + 1) - firstSample) * (pcmPosition - intPCMPosition);
		} else {
			sample = firstSample;
		}

		float newPCMPosition = pcmPosition + positionDelta;
		if (pcmWaveLooped) {
			newPCMPosition = fmod(newPCMPosition, (float)pcmWaveLength);
		}
		pcmPosition = newPCMPosition;
	} else {
		// Render synthesised waveform
		wavePos *= lastFreq / freq;
		lastFreq = freq;

		float resAmp = EXP2F(1.0f - (32 - resonance) / 4.0f);
		{
			//static const float resAmpFactor = EXP2F(-7);
			//resAmp = EXP2I(resonance << 10) * resAmpFactor;
		}

		// The cutoffModifier may not be supposed to be directly added to the cutoff -
		// it may for example need to be multiplied in some way.
		// 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.
		float cutoffVal = cutoffRampVal / 262144.0f;
		if (cutoffVal > MAX_CUTOFF_VALUE) {
			cutoffVal = MAX_CUTOFF_VALUE;
		}

		// Wave length in samples
		float waveLen = SAMPLE_RATE / freq;

		// Init cosineLen
		float cosineLen = 0.5f * waveLen;
		if (cutoffVal > MIDDLE_CUTOFF_VALUE) {
			cosineLen *= EXP2F((cutoffVal - MIDDLE_CUTOFF_VALUE) / -16.0f); // found from sample analysis
		}

		// Start playing in center of first cosine segment
		// relWavePos is shifted by a half of cosineLen
		float relWavePos = wavePos + 0.5f * cosineLen;
		if (relWavePos > waveLen) {
			relWavePos -= waveLen;
		}

		// Ratio of positive segment to wave length
		float pulseLen = 0.5f;
		if (pulseWidth > 128) {
			pulseLen = EXP2F((64 - pulseWidth) / 64.0f);
			//static const float pulseLenFactor = EXP2F(-192 / 64);
			//pulseLen = EXP2I((256 - pulseWidthVal) << 6) * pulseLenFactor;
		}
		pulseLen *= waveLen;

		float hLen = pulseLen - cosineLen;

		// Ignore pulsewidths too high for given freq
		if (hLen < 0.0f) {
			hLen = 0.0f;
		}

		// Ignore pulsewidths too high for given freq and cutoff
		float lLen = waveLen - hLen - 2 * cosineLen;
		if (lLen < 0.0f) {
			lLen = 0.0f;
		}

		// Correct resAmp for cutoff in range 50..66
		if ((cutoffVal >= 128.0f) && (cutoffVal < 144.0f)) {
			resAmp *= sin(FLOAT_PI * (cutoffVal - 128.0f) / 32.0f);
		}

		// Produce filtered square wave with 2 cosine waves on slopes

		// 1st cosine segment
		if (relWavePos < cosineLen) {
			sample = -cos(FLOAT_PI * relWavePos / cosineLen);
		} else

		// high linear segment
		if (relWavePos < (cosineLen + hLen)) {
			sample = 1.f;
		} else

		// 2nd cosine segment
		if (relWavePos < (2 * cosineLen + hLen)) {
			sample = cos(FLOAT_PI * (relWavePos - (cosineLen + hLen)) / cosineLen);
		} else {

		// low linear segment
			sample = -1.f;
		}

		if (cutoffVal < 128.0f) {

			// Attenuate samples below cutoff 50
			// Found by sample analysis
			sample *= EXP2F(-0.125f * (128.0f - cutoffVal));
		} else {

			// Add resonance sine. Effective for cutoff > 50 only
			float resSample = 1.0f;

			// Resonance decay speed factor
			float resAmpDecayFactor = Tables::getInstance().resAmpDecayFactor[resonance >> 2];

			// Now relWavePos counts from the middle of first cosine
			relWavePos = wavePos;

			// negative segments
			if (!(relWavePos < (cosineLen + hLen))) {
				resSample = -resSample;
				relWavePos -= cosineLen + hLen;

				// From the digital captures, the decaying speed of the resonance sine is found a bit different for the positive and the negative segments
				resAmpDecayFactor += 0.25f;
			}

			// Resonance sine WG
			resSample *= sin(FLOAT_PI * relWavePos / cosineLen);

			// Resonance sine amp
			float resAmpFadeLog2 = -0.125f * resAmpDecayFactor * (relWavePos / cosineLen); // seems to be exact
			float resAmpFade = EXP2F(resAmpFadeLog2);

			// Now relWavePos set negative to the left from center of any cosine
			relWavePos = wavePos;

			// negative segment
			if (!(wavePos < (waveLen - 0.5f * cosineLen))) {
				relWavePos -= waveLen;
			} else

			// positive segment
			if (!(wavePos < (hLen + 0.5f * cosineLen))) {
				relWavePos -= cosineLen + hLen;
			}

			// 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 (relWavePos < 0.5f * cosineLen) {
				float syncSine = sin(FLOAT_PI * relWavePos / cosineLen);
				if (relWavePos < 0.0f) {
					// The window is synchronous square sine here
					resAmpFade *= syncSine * syncSine;
				} else {
					// The window is synchronous sine here
					resAmpFade *= syncSine;
				}
			}

			sample += resSample * resAmp * resAmpFade;
		}

		// sawtooth waves
		if (sawtoothWaveform) {
			sample *= cos(FLOAT_2PI * wavePos / waveLen);
		}

		wavePos++;

		// wavePos isn't supposed to be > waveLen
		if (wavePos > waveLen) {
			wavePos -= waveLen;
		}
	}

	// Multiply sample with current TVA value
	sample *= amp;
	return sample;
}

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

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

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

void LA32PartialPair::init(const bool ringModulated, const bool mixed) {
	this->ringModulated = ringModulated;
	this->mixed = mixed;
	masterOutputSample = 0.0f;
	slaveOutputSample = 0.0f;
}

void LA32PartialPair::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 LA32PartialPair::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 LA32PartialPair::generateNextSample(const PairType useMaster, const Bit32u amp, const Bit16u pitch, const Bit32u cutoff) {
	if (useMaster == MASTER) {
		masterOutputSample = master.generateNextSample(amp, pitch, cutoff);
	} else {
		slaveOutputSample = slave.generateNextSample(amp, pitch, cutoff);
	}
}

Bit16s LA32PartialPair::nextOutSample() {
	float outputSample;
	if (ringModulated) {
		float ringModulatedSample = masterOutputSample * slaveOutputSample;
		outputSample = mixed ? masterOutputSample + ringModulatedSample : ringModulatedSample;
	} else {
		outputSample = masterOutputSample + slaveOutputSample;
	}
	return Bit16s(outputSample * 8192.0f);
}

void LA32PartialPair::deactivate(const PairType useMaster) {
	if (useMaster == MASTER) {
		master.deactivate();
		masterOutputSample = 0.0f;
	} else {
		slave.deactivate();
		slaveOutputSample = 0.0f;
	}
}

bool LA32PartialPair::isActive(const PairType useMaster) const {
	return useMaster == MASTER ? master.isActive() : slave.isActive();
}

}

#endif // #if MT32EMU_ACCURATE_WG == 1