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sketches/sketch_zx.ino

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+/*
+"Tri-Shape", a wave shaping  oscilatorfor Ginkosynthese's "grains" module.
+	By Kassen Oud
+
+LICENSE:
+This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 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 General Public License for more details.
+	
+	You should have received a copy of the GNU General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+DESCRIPION;
+	A triangle-based osclitator with wave-folding and hard-clipping features.
+
+MANUAL;
+	Knob 1 / mod 1; Wave folding
+		Amplifies the base triangle wave, then once it hits the limits of the
+		range "folds" it back in the opposite direction. With enough
+		amplification this will happen again at the other side, creating a
+		rich spectrum.
+	Knob 2/ mod 2; Hard Cliping
+		Amplifies the signal (after the folding) and clips the result. This is
+		done asymetrically for a "deeper" and more "balsy" sound. Thanks to
+		Rob Bothof for that trick.
+	Knob 3: Base Tuning.
+		Sets the base pitch.
+	Mod 3; Pitch Modulation
+		This CV gets added to the value set by Knob 3.
+
+*/
+		
+
+
+//the libraries we use
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/pgmspace.h>
+
+//variables
+uint16_t phase_accumulator;		//keeps track of the phase
+uint16_t phase_inc;				//phase increase per sample
+bool flip = false;				//keeps track of the output's polarity
+uint16_t wrap = 1;				// amount of wave-folding
+uint16_t drive = 32;			//amount of clipping for positive signal
+uint16_t top_drive = 32;		//same for negative signal
+uint16_t output = 127;			//the value we write out
+uint16_t last_out = 127;		//last value we wrote out
+
+// Map inputs
+#define DRIVE_CONTROL		(A1)
+#define WRAP_CONTROL		(A2)
+#define PITCH_KNOB			(A0)
+#define PITCH_CV			(A3)
+
+// Changing these will also requires rewriting setup()
+//    Output is on pin 11
+#define PWM_PIN       11
+#define PWM_VALUE     OCR2A
+#define LED_PORT      PORTB
+#define LED_BIT       5
+#define PWM_INTERRUPT TIMER2_OVF_vect
+
+//maps cv to samples of phase increase each time we output a new value
+//this might need tuning in the future
+const uint16_t freqTable[] PROGMEM = {
+  69,  69,  69,  69,  70,  70,  70,  70,  70,  71,			//   0 to 9
+  71,  71,  71,  72,  72,  72,  72,  73,  73,  73,			//  
+  73,  74,  74,  74,  74,  75,  75,  75,  75,  76,			//  
+  76,  76,  76,  77,  77,  77,  77,  78,  78,  78,			//  
+  78,  79,  79,  79,  79,  80,  80,  80,  81,  81,			//  
+  81,  81,  82,  82,  82,  82,  83,  83,  83,  84,			//  
+  84,  84,  84,  85,  85,  85,  86,  86,  86,  86,			//  
+  87,  87,  87,  88,  88,  88,  88,  89,  89,  89,			//  
+  90,  90,  90,  91,  91,  91,  91,  92,  92,  92,			//  
+  93,  93,  93,  94,  94,  94,  95,  95,  95,  96,			//  
+  96,  96,  97,  97,  97,  97,  98,  98,  98,  99,			//  100 to 109
+  99,  99, 100, 100, 100, 101, 101, 101, 102, 102,			//  
+ 102, 103, 103, 104, 104, 104, 105, 105, 105, 106,			//  
+ 106, 106, 107, 107, 107, 108, 108, 109, 109, 109,			//  
+ 110, 110, 110, 111, 111, 111, 112, 112, 113, 113,			//  
+ 113, 114, 114, 114, 115, 115, 116, 116, 116, 117,			//  
+ 117, 118, 118, 118, 119, 119, 120, 120, 120, 121,			//  
+ 121, 122, 122, 122, 123, 123, 124, 124, 124, 125,			//  
+ 125, 126, 126, 127, 127, 127, 128, 128, 129, 129,			//  
+ 130, 130, 130, 131, 131, 132, 132, 133, 133, 134,			//  
+ 134, 134, 135, 135, 136, 136, 137, 137, 138, 138,			//  200 to 209
+ 139, 139, 139, 140, 140, 141, 141, 142, 142, 143,			//  
+ 143, 144, 144, 145, 145, 146, 146, 147, 147, 148,			//  
+ 148, 149, 149, 150, 150, 151, 151, 152, 152, 153,			//  
+ 153, 154, 154, 155, 155, 156, 156, 157, 157, 158,			//  
+ 158, 159, 159, 160, 161, 161, 162, 162, 163, 163,			//  
+ 164, 164, 165, 165, 166, 167, 167, 168, 168, 169,			//  
+ 169, 170, 171, 171, 172, 172, 173, 173, 174, 175,			//  
+ 175, 176, 176, 177, 178, 178, 179, 179, 180, 181,			//  
+ 181, 182, 182, 183, 184, 184, 185, 185, 186, 187,			//  
+ 187, 188, 189, 189, 190, 190, 191, 192, 192, 193,			//  300 to 309
+ 194, 194, 195, 196, 196, 197, 198, 198, 199, 200,			//  
+ 200, 201, 202, 202, 203, 204, 204, 205, 206, 206,			//  
+ 207, 208, 208, 209, 210, 211, 211, 212, 213, 213,			//  
+ 214, 215, 216, 216, 217, 218, 218, 219, 220, 221,			//  
+ 221, 222, 223, 224, 224, 225, 226, 227, 227, 228,			//  
+ 229, 230, 231, 231, 232, 233, 234, 234, 235, 236,			//  
+ 237, 238, 238, 239, 240, 241, 242, 242, 243, 244,			//  
+ 245, 246, 246, 247, 248, 249, 250, 251, 251, 252,			//  
+ 253, 254, 255, 256, 257, 257, 258, 259, 260, 261,			//  
+ 262, 263, 264, 264, 265, 266, 267, 268, 269, 270,			//  400 to 409
+ 271, 272, 273, 273, 274, 275, 276, 277, 278, 279,			//  
+ 280, 281, 282, 283, 284, 285, 286, 287, 288, 288,			//  
+ 289, 290, 291, 292, 293, 294, 295, 296, 297, 298,			//  
+ 299, 300, 301, 302, 303, 304, 305, 306, 307, 308,			//  
+ 310, 311, 312, 313, 314, 315, 316, 317, 318, 319,			//  
+ 320, 321, 322, 323, 324, 325, 327, 328, 329, 330,			//  
+ 331, 332, 333, 334, 335, 337, 338, 339, 340, 341,			//  
+ 342, 343, 345, 346, 347, 348, 349, 350, 352, 353,			//  
+ 354, 355, 356, 357, 359, 360, 361, 362, 363, 365,			//  
+ 366, 367, 368, 370, 371, 372, 373, 375, 376, 377,			//  500 to 509
+ 378, 380, 381, 382, 383, 385, 386, 387, 389, 390,			//  
+ 391, 393, 394, 395, 397, 398, 399, 401, 402, 403,			//  
+ 405, 406, 407, 409, 410, 411, 413, 414, 416, 417,			//  
+ 418, 420, 421, 423, 424, 425, 427, 428, 430, 431,			//  
+ 433, 434, 436, 437, 438, 440, 441, 443, 444, 446,			//  
+ 447, 449, 450, 452, 453, 455, 456, 458, 460, 461,			//  
+ 463, 464, 466, 467, 469, 470, 472, 474, 475, 477,			//  
+ 478, 480, 482, 483, 485, 486, 488, 490, 491, 493,			//  
+ 495, 496, 498, 500, 501, 503, 505, 506, 508, 510,			//  
+ 511, 513, 515, 517, 518, 520, 522, 524, 525, 527,			//  600 to 609
+ 529, 531, 532, 534, 536, 538, 540, 541, 543, 545,			//  
+ 547, 549, 551, 552, 554, 556, 558, 560, 562, 564,			//  
+ 566, 567, 569, 571, 573, 575, 577, 579, 581, 583,			//  
+ 585, 587, 589, 591, 593, 595, 597, 599, 601, 603,			//  
+ 605, 607, 609, 611, 613, 615, 617, 619, 621, 623,			//  
+ 625, 627, 630, 632, 634, 636, 638, 640, 642, 644,			//  
+ 647, 649, 651, 653, 655, 658, 660, 662, 664, 666,			//  
+ 669, 671, 673, 675, 678, 680, 682, 685, 687, 689,			//  
+ 691, 694, 696, 698, 701, 703, 705, 708, 710, 713,			//  
+ 715, 717, 720, 722, 725, 727, 729, 732, 734, 737,			//  700 to 709
+ 739, 742, 744, 747, 749, 752, 754, 757, 759, 762,			//  
+ 764, 767, 770, 772, 775, 777, 780, 783, 785, 788,			//  
+ 791, 793, 796, 799, 801, 804, 807, 809, 812, 815,			//  
+ 817, 820, 823, 826, 828, 831, 834, 837, 840, 842,			//  
+ 845, 848, 851, 854, 857, 860, 862, 865, 868, 871,			//  
+ 874, 877, 880, 883, 886, 889, 892, 895, 898, 901,			//  
+ 904, 907, 910, 913, 916, 919, 922, 925, 928, 932,			//  
+ 935, 938, 941, 944, 947, 950, 954, 957, 960, 963,			//  
+ 966, 970, 973, 976, 979, 983, 986, 989, 993, 996,			//  
+ 999,1003,1006,1009,1013,1016,1020,1023,1027,1030,			//  800 to 809
+1033,1037,1040,1044,1047,1051,1054,1058,1061,1065,			//  
+1069,1072,1076,1079,1083,1087,1090,1094,1098,1101,			//  
+1105,1109,1112,1116,1120,1124,1127,1131,1135,1139,			//  
+1143,1146,1150,1154,1158,1162,1166,1170,1174,1178,			//  
+1182,1186,1189,1193,1197,1201,1206,1210,1214,1218,			//  
+1222,1226,1230,1234,1238,1242,1247,1251,1255,1259,			//  
+1263,1268,1272,1276,1280,1285,1289,1293,1298,1302,			//  
+1306,1311,1315,1320,1324,1328,1333,1337,1342,1346,			//  
+1351,1355,1360,1365,1369,1374,1378,1383,1388,1392,			//  
+1397,1402,1406,1411,1416,1421,1425,1430,1435,1440,			//  900 to 909
+1444,1449,1454,1459,1464,1469,1474,1479,1484,1489,			//  
+1494,1499,1504,1509,1514,1519,1524,1529,1534,1539,			//  
+1545,1550,1555,1560,1565,1571,1576,1581,1587,1592,			//  
+1597,1603,1608,1613,1619,1624,1630,1635,1641,1646,			//  
+1652,1657,1663,1668,1674,1679,1685,1691,1696,1702,			//  
+1708,1714,1719,1725,1731,1737,1742,1748,1754,1760,			//  
+1766,1772,1778,1784,1790,1796,1802,1808,1814,1820,			//  
+1826,1832,1838,1845,1851,1857,1863,1869,1876,1882,			//  
+1888,1895,1901,1907,1914,1920,1927,1933,1940,1946,			//  
+1953,1959,1966,1972,1979,1986,1992,1999,2006,2012,			//  1000 to 1009
+2019,2026,2033,2040,2046,2053,2060,2067,2074,2081,			//  1010 to 1019
+2088,2095,2102,2109                              ,			//  1020 to 1023
+};
+
+uint16_t mapFreq(uint16_t input)
+{
+	return pgm_read_word_near(freqTable + input);
+}
+
+//sets up pins and configures the samplerate and frequency of the PWM output
+void setup()
+{
+	TCCR2A = _BV(COM2A1) | _BV(WGM20);
+	TCCR2B = _BV(CS20);
+	TIMSK2 = _BV(TOIE2);
+	pinMode(PWM_PIN,OUTPUT);
+	PWM_VALUE = 127;
+}
+
+//reads modulation inputs
+void loop()
+{
+	//calculate the pitch
+	int pwmv = min( 1023,  analogRead(PITCH_CV) + analogRead(PITCH_KNOB));
+	//look up the phase increase per sample
+	phase_inc = mapFreq(pwmv);
+	//read the control for wave-folding
+	wrap =  min( 64 + (analogRead(WRAP_CONTROL) >> 1), 511);
+	//read the control for clipping and calculate the two amounts of overdrive
+	drive = min( 32 + (analogRead(DRIVE_CONTROL) >> 1), 511);
+	top_drive = max( 32, drive >>1);
+}
+
+//Actual sound generation happens here.
+//This involves rather a lot of bitwise operations, if you're looking to get
+//into writing code for the Grains I'd suggest not starting here; "PWM-Saw" is
+//far more "friendly". That's a nice way of saying "Here be Dragons".
+//I'm writing numbers out as literal trains of 0's and 1's because we make fair
+//ampount of use of those. Also note that a lot of the structure for this is
+//caused by avoiding signed integers, while we do want a symetrical signal.
+//Hence; we treat it as a unipolar signal, keep track of the polarity it should
+//be and apply that at the end.
+//I drew the process out on graph paper using multicoloured fineliner.
+//If you're serious about following all of this that might help.
+SIGNAL(PWM_INTERRUPT)
+{
+	//increase the phase
+	phase_accumulator += phase_inc;
+	//2nd half of the phase will be the negative part of the cycle
+	flip = phase_accumulator & 0b1000000000000000;
+	//turn the phase acumulator into 4 up-ramps
+	output = (phase_accumulator &  0b0011111111111111);
+	//get these into 7 bit range. "flip" will be the 8th bit of the output
+	output = output >> 7;
+	//invert the 2nd and 4th of our 4 up-ramps to create our triangle wave
+	if (phase_accumulator & 0b0100000000000000) output = (uint16_t)127 - output;
+
+	//amplify the signal for the wave-wrapping
+	output *= wrap;
+	output = output >> 6;
+	//detect whether folding will be more involved than inverting the range
+	//from 128 to 254
+	if (output & 0b1111111100000000) 
+	{
+		//values between 255 and 511 fold back past the "0" line
+		if (output & 0b0000000100000000) flip = !flip;
+		//mask out bits beyond which the process just repeats
+		output &= 0b0000000011111111;
+	}
+	//actual folding
+	if (output > (uint16_t)127)
+	{
+		output = 127 - (output & 0b0000000001111111);
+	}
+
+	//apply the signal gain for asymetrical clipping
+	output *= flip?drive:top_drive;
+	output = output >> 5;
+	//clip
+	if (output >  (uint16_t)127) output = (uint16_t)127;
+
+	//turn our 7bit unipolar value into a 8bit bipolar one
+	if ( flip ) output = (uint16_t)127 - output;
+	else output += (uint16_t)127;
+
+	//slight amount of smoothing
+	output = (output + last_out) >> 1;
+	last_out = output;
+	
+	//write out the output
+	PWM_VALUE = output;
+}