Band limited versions of square and sawtooth added to AudioSynthWaveform and AudioSynthWaveformModulated

data_bandlimit_step.c

+#include <stdint.h>
+
+// band limited step function, 17kHz limit for 44.1kSPS.
+// step goes from -BASE_AMPLITUDE to +BASE_AMPLITUDE nominally
+// [ only store the first half of the table due to its odd symmetry ]
+// the extra first entry allows for the interpolation code not to overrun on reflected table,
+// the last extra entry allows for interpolation not to overrun when non-reflected
+
+const int16_t step_table [258] =  //   size is N/2+2  where  N = SUPPORT * SCALE * 2
+{
+ -24576,
+ -24551, -24550, -24549, -24548, -24546, -24544, -24542, -24540, -24538, -24537, -24537, -24537, -24539, -24543, -24547, -24553,
+ -24560, -24569, -24579, -24590, -24602, -24614, -24627, -24639, -24651, -24663, -24673, -24682, -24689, -24693, -24695, -24694,
+ -24691, -24684, -24674, -24661, -24646, -24627, -24607, -24585, -24561, -24536, -24511, -24486, -24463, -24441, -24421, -24403,
+ -24390, -24380, -24374, -24373, -24377, -24386, -24400, -24418, -24441, -24469, -24499, -24533, -24569, -24607, -24645, -24683,
+ -24720, -24755, -24786, -24814, -24836, -24854, -24865, -24870, -24867, -24858, -24842, -24819, -24789, -24753, -24712, -24666,
+ -24617, -24566, -24513, -24460, -24408, -24359, -24314, -24274, -24239, -24212, -24193, -24182, -24181, -24189, -24206, -24233,
+ -24268, -24312, -24364, -24422, -24485, -24552, -24621, -24691, -24760, -24826, -24889, -24945, -24994, -25034, -25064, -25084,
+ -25091, -25087, -25070, -25041, -25000, -24948, -24886, -24815, -24736, -24652, -24564, -24473, -24383, -24296, -24213, -24136,
+ -24068, -24011, -23965, -23934, -23916, -23914, -23928, -23958, -24003, -24064, -24137, -24224, -24320, -24426, -24537, -24653,
+ -24769, -24884, -24994, -25097, -25190, -25271, -25337, -25387, -25418, -25430, -25422, -25394, -25345, -25276, -25188, -25084,
+ -24964, -24832, -24691, -24542, -24391, -24240, -24092, -23953, -23824, -23710, -23613, -23537, -23484, -23456, -23454, -23478,
+ -23531, -23610, -23714, -23843, -23993, -24162, -24347, -24542, -24745, -24950, -25153, -25348, -25531, -25697, -25841, -25960,
+ -26048, -26104, -26125, -26108, -26054, -25961, -25831, -25665, -25466, -25238, -24984, -24710, -24422, -24125, -23828, -23535,
+ -23256, -22998, -22766, -22570, -22414, -22304, -22246, -22244, -22300, -22417, -22594, -22831, -23126, -23475, -23872, -24311,
+ -24785, -25283, -25795, -26311, -26816, -27300, -27747, -28143, -28476, -28731, -28894, -28953, -28896, -28711, -28390, -27923,
+ -27305, -26530, -25596, -24501, -23246, -21836, -20274, -18569, -16729, -14766, -12691, -10521,  -8269,  -5953,  -3591,  -1200,
+  1200
+};
+
+/* // this version is for SCALE = 64, but with interpolation isn't really needed
+int16_t edge_table [1026] =  //   size is N/2+2  where  N = SUPPORT * SCALE * 2
+{
+ -24576,
+ -24551, -24551, -24551, -24551, -24551, -24550, -24550, -24550, -24550, -24549, -24549, -24549, -24548, -24548, -24547, -24547,
+ -24547, -24546, -24546, -24545, -24544, -24544, -24543, -24543, -24542, -24542, -24541, -24541, -24540, -24540, -24539, -24539,
+ -24539, -24538, -24538, -24538, -24537, -24537, -24537, -24537, -24537, -24537, -24537, -24537, -24537, -24537, -24538, -24538,
+ -24539, -24539, -24540, -24540, -24541, -24542, -24543, -24544, -24545, -24546, -24548, -24549, -24551, -24552, -24554, -24556,
+ -24557, -24559, -24561, -24563, -24566, -24568, -24570, -24573, -24575, -24578, -24580, -24583, -24586, -24588, -24591, -24594,
+ -24597, -24600, -24603, -24606, -24609, -24612, -24616, -24619, -24622, -24625, -24628, -24631, -24635, -24638, -24641, -24644,
+ -24647, -24650, -24653, -24656, -24659, -24661, -24664, -24667, -24669, -24672, -24674, -24677, -24679, -24681, -24683, -24685,
+ -24686, -24688, -24689, -24690, -24692, -24693, -24693, -24694, -24695, -24695, -24695, -24695, -24695, -24694, -24694, -24693,
+ -24692, -24691, -24690, -24688, -24687, -24685, -24683, -24680, -24678, -24675, -24672, -24669, -24666, -24663, -24659, -24656,
+ -24652, -24648, -24643, -24639, -24634, -24630, -24625, -24620, -24615, -24609, -24604, -24599, -24593, -24587, -24582, -24576,
+ -24570, -24564, -24558, -24552, -24545, -24539, -24533, -24527, -24520, -24514, -24508, -24502, -24496, -24489, -24483, -24477,
+ -24471, -24466, -24460, -24454, -24449, -24443, -24438, -24433, -24428, -24423, -24418, -24414, -24410, -24406, -24402, -24398,
+ -24395, -24391, -24388, -24386, -24383, -24381, -24379, -24377, -24376, -24375, -24374, -24374, -24373, -24373, -24374, -24374,
+ -24375, -24377, -24378, -24380, -24382, -24385, -24388, -24391, -24394, -24398, -24402, -24406, -24411, -24416, -24421, -24427,
+ -24432, -24438, -24445, -24451, -24458, -24465, -24472, -24480, -24488, -24496, -24504, -24512, -24520, -24529, -24538, -24547,
+ -24556, -24565, -24574, -24583, -24593, -24602, -24612, -24621, -24631, -24641, -24650, -24660, -24669, -24679, -24688, -24697,
+ -24706, -24715, -24724, -24733, -24742, -24750, -24759, -24767, -24775, -24782, -24790, -24797, -24804, -24810, -24817, -24823,
+ -24828, -24834, -24839, -24843, -24848, -24852, -24855, -24858, -24861, -24864, -24866, -24867, -24868, -24869, -24869, -24869,
+ -24869, -24868, -24866, -24864, -24862, -24859, -24856, -24852, -24848, -24844, -24839, -24834, -24828, -24822, -24815, -24808,
+ -24800, -24793, -24784, -24776, -24767, -24758, -24748, -24738, -24728, -24717, -24706, -24695, -24684, -24672, -24660, -24648,
+ -24636, -24623, -24611, -24598, -24585, -24572, -24559, -24546, -24533, -24520, -24506, -24493, -24480, -24467, -24454, -24441,
+ -24428, -24415, -24402, -24390, -24377, -24365, -24354, -24342, -24331, -24320, -24309, -24298, -24288, -24279, -24269, -24260,
+ -24252, -24243, -24236, -24228, -24222, -24215, -24210, -24204, -24199, -24195, -24191, -24188, -24186, -24183, -24182, -24181,
+ -24181, -24181, -24182, -24183, -24185, -24188, -24191, -24194, -24199, -24204, -24209, -24215, -24222, -24229, -24237, -24245,
+ -24254, -24264, -24274, -24284, -24295, -24307, -24319, -24331, -24344, -24357, -24371, -24385, -24399, -24414, -24429, -24445,
+ -24461, -24477, -24493, -24510, -24526, -24543, -24560, -24577, -24595, -24612, -24630, -24647, -24665, -24682, -24700, -24717,
+ -24734, -24751, -24768, -24785, -24802, -24818, -24834, -24850, -24866, -24881, -24896, -24910, -24924, -24938, -24951, -24964,
+ -24976, -24988, -24999, -25010, -25020, -25029, -25038, -25046, -25054, -25061, -25067, -25072, -25077, -25081, -25085, -25087,
+ -25089, -25091, -25091, -25091, -25090, -25088, -25085, -25082, -25077, -25073, -25067, -25060, -25053, -25045, -25036, -25027,
+ -25017, -25006, -24994, -24982, -24969, -24955, -24941, -24926, -24910, -24894, -24878, -24860, -24842, -24824, -24805, -24786,
+ -24766, -24746, -24726, -24705, -24684, -24663, -24641, -24619, -24597, -24575, -24552, -24530, -24507, -24485, -24462, -24440,
+ -24417, -24395, -24372, -24350, -24328, -24307, -24285, -24264, -24243, -24223, -24203, -24183, -24164, -24145, -24127, -24110,
+ -24093, -24076, -24061, -24046, -24031, -24018, -24005, -23993, -23981, -23971, -23961, -23952, -23944, -23937, -23931, -23926,
+ -23922, -23918, -23916, -23914, -23914, -23914, -23916, -23918, -23922, -23926, -23932, -23938, -23946, -23954, -23964, -23974,
+ -23985, -23997, -24011, -24025, -24040, -24056, -24073, -24090, -24109, -24128, -24148, -24169, -24190, -24213, -24236, -24259,
+ -24283, -24308, -24334, -24359, -24386, -24413, -24440, -24467, -24495, -24523, -24552, -24581, -24609, -24638, -24667, -24697,
+ -24726, -24755, -24784, -24813, -24841, -24870, -24898, -24926, -24953, -24980, -25007, -25034, -25059, -25084, -25109, -25133,
+ -25156, -25179, -25201, -25222, -25242, -25261, -25280, -25297, -25314, -25329, -25344, -25357, -25370, -25381, -25391, -25400,
+ -25408, -25415, -25420, -25425, -25428, -25429, -25430, -25429, -25427, -25424, -25419, -25413, -25406, -25398, -25388, -25377,
+ -25365, -25351, -25336, -25320, -25303, -25285, -25265, -25244, -25223, -25200, -25176, -25150, -25124, -25097, -25069, -25040,
+ -25010, -24980, -24948, -24916, -24883, -24849, -24815, -24780, -24745, -24709, -24672, -24635, -24598, -24561, -24523, -24486,
+ -24448, -24410, -24372, -24334, -24296, -24258, -24221, -24184, -24147, -24111, -24075, -24039, -24004, -23970, -23936, -23903,
+ -23871, -23840, -23809, -23780, -23751, -23724, -23697, -23672, -23648, -23625, -23603, -23583, -23564, -23546, -23530, -23515,
+ -23502, -23490, -23480, -23471, -23464, -23459, -23455, -23453, -23452, -23453, -23456, -23461, -23467, -23475, -23485, -23496,
+ -23509, -23524, -23540, -23558, -23578, -23599, -23622, -23647, -23673, -23701, -23730, -23761, -23793, -23826, -23861, -23898,
+ -23935, -23974, -24014, -24055, -24098, -24141, -24185, -24230, -24277, -24323, -24371, -24419, -24468, -24518, -24568, -24618,
+ -24669, -24720, -24771, -24822, -24873, -24925, -24976, -25027, -25077, -25128, -25178, -25227, -25276, -25324, -25371, -25418,
+ -25464, -25509, -25552, -25595, -25636, -25677, -25715, -25753, -25789, -25824, -25856, -25888, -25917, -25945, -25971, -25995,
+ -26017, -26038, -26056, -26072, -26086, -26098, -26107, -26115, -26120, -26123, -26123, -26121, -26117, -26111, -26102, -26091,
+ -26077, -26061, -26043, -26022, -25999, -25973, -25945, -25915, -25883, -25848, -25811, -25772, -25730, -25687, -25641, -25593,
+ -25543, -25492, -25438, -25383, -25326, -25267, -25207, -25145, -25081, -25016, -24950, -24883, -24815, -24745, -24675, -24603,
+ -24531, -24458, -24385, -24311, -24237, -24163, -24088, -24014, -23939, -23865, -23791, -23717, -23644, -23572, -23500, -23429,
+ -23360, -23291, -23224, -23157, -23093, -23030, -22968, -22908, -22851, -22795, -22741, -22690, -22640, -22594, -22549, -22508,
+ -22469, -22432, -22399, -22369, -22341, -22317, -22296, -22278, -22264, -22253, -22245, -22241, -22240, -22243, -22250, -22261,
+ -22275, -22292, -22314, -22339, -22368, -22401, -22438, -22479, -22523, -22571, -22623, -22678, -22738, -22801, -22867, -22938,
+ -23011, -23088, -23169, -23253, -23340, -23430, -23524, -23620, -23719, -23822, -23926, -24034, -24144, -24256, -24370, -24487,
+ -24605, -24725, -24847, -24970, -25094, -25220, -25347, -25474, -25602, -25731, -25860, -25989, -26118, -26246, -26374, -26502,
+ -26628, -26753, -26877, -27000, -27121, -27240, -27356, -27471, -27582, -27691, -27797, -27900, -27999, -28095, -28186, -28274,
+ -28357, -28436, -28509, -28578, -28642, -28700, -28753, -28800, -28841, -28875, -28903, -28925, -28940, -28947, -28948, -28941,
+ -28927, -28905, -28875, -28837, -28791, -28737, -28674, -28602, -28522, -28432, -28334, -28227, -28110, -27984, -27849, -27704,
+ -27549, -27385, -27211, -27027, -26833, -26629, -26416, -26192, -25959, -25715, -25461, -25198, -24924, -24640, -24346, -24043,
+ -23729, -23406, -23073, -22730, -22377, -22015, -21643, -21262, -20872, -20472, -20063, -19646, -19220, -18785, -18341, -17889,
+ -17429, -16961, -16486, -16002, -15511, -15013, -14508, -13996, -13477, -12953, -12421, -11884, -11342, -10794, -10240,  -9682,
+  -9119,  -8552,  -7980,  -7405,  -6826,  -6243,  -5658,  -5070,  -4479,  -3887,  -3292,  -2696,  -2098,  -1499,   -900,   -300,
+    300
+} ;
+*/

keywords.txt

 WAVEFORM_SAWTOOTH_REVERSE	LITERAL1
 WAVEFORM_SAMPLE_HOLD	LITERAL1
 WAVEFORM_TRIANGLE_VARIABLE	LITERAL1
+WAVEFORM_BANDLIMIT_SAWTOOTH	LITERAL1
+WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE	LITERAL1
+WAVEFORM_BANDLIMIT_SQUARE	LITERAL1
 
 AUDIO_MEMORY_23LC1024	LITERAL1
 AUDIO_MEMORY_MEMORYBOARD	LITERAL1

synth_waveform.cpp

 		}
 		break;
 
+	case WAVEFORM_BANDLIMIT_SQUARE:
+		for (int i = 0 ; i < AUDIO_BLOCK_SAMPLES ; i++)
+		{
+		  uint32_t new_ph = ph + inc ;
+		  int16_t val = band_limit_waveform.generate_square (new_ph, i) ;
+		  *bp++ = (val * magnitude) >> 16 ;
+		  ph = new_ph ;
+		}
+		break;
+
 	case WAVEFORM_SAWTOOTH:
 		for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
 			*bp++ = signed_multiply_32x16t(magnitude, ph);
 		}
 		break;
 
+	case WAVEFORM_BANDLIMIT_SAWTOOTH:
+	case WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE:
+		for (i = 0 ; i < AUDIO_BLOCK_SAMPLES; i++)
+		{
+		  uint32_t new_ph = ph + inc ;
+		  int16_t val = band_limit_waveform.generate_sawtooth (new_ph, i) ;
+		  if (tone_type == WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE)
+		    *bp++ = (val * -magnitude) >> 16 ;
+		  else
+		    *bp++ = (val * magnitude) >> 16 ;
+		  ph = new_ph ;
+		}
+		break;
+
 	case WAVEFORM_TRIANGLE:
 		for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
 			uint32_t phtop = ph >> 30;
 			// exp2 algorithm by Laurent de Soras
 			// https://www.musicdsp.org/en/latest/Other/106-fast-exp2-approximation.html
 			n = (n + 134217728) << 3;
+
 			n = multiply_32x32_rshift32_rounded(n, n);
 			n = multiply_32x32_rshift32_rounded(n, 715827883) << 3;
 			n = n + 715827882;
 		}
 		break;
 
+	case WAVEFORM_BANDLIMIT_SQUARE:
+		for (i = 0 ; i < AUDIO_BLOCK_SAMPLES ; i++)
+		{
+		  int32_t val = band_limit_waveform.generate_square (phasedata[i], i) ;
+		  *bp++ = val ; /// (int16_t) ((val * magnitude) >> 16) ;
+		}
+		break;
+
 	case WAVEFORM_SAWTOOTH:
 		for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
 			*bp++ = signed_multiply_32x16t(magnitude, phasedata[i]);
 		}
 		break;
 
+	case WAVEFORM_BANDLIMIT_SAWTOOTH:
+	case WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE:
+		for (i = 0 ; i < AUDIO_BLOCK_SAMPLES ; i++)
+		{
+		  int16_t val = band_limit_waveform.generate_sawtooth (phasedata[i], i) ;
+		  ///val = (int16_t) ((val * magnitude) >> 16) ;
+		  *bp++ = tone_type == WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE ? (int16_t) -val : (int16_t) +val ;
+		}
+		break;
+
 	case WAVEFORM_TRIANGLE_VARIABLE:
 		if (shapedata) {
 			for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
 }
 
 
+// BandLimitedWaveform
+
+
+#define SUPPORT_SHIFT 4
+#define SUPPORT (1 << SUPPORT_SHIFT)
+#define PTRMASK ((2 << SUPPORT_SHIFT) - 1)
+
+#define SCALE 16
+#define SCALE_MASK (SCALE-1)
+#define N (SCALE * SUPPORT * 2)
+
+#define GUARD_BITS 8
+#define GUARD      (1 << GUARD_BITS)
+#define HALF_GUARD (1 << (GUARD_BITS-1))
+
+
+#define BASE_AMPLITUDE 0x6000  // 0x7fff won't work due to Gibb's phenomenon, so use 3/4 of full range.
+
+#define DEG180 0x80000000u
+
+#define PHASE_SCALE (0x100000000L / (2 * BASE_AMPLITUDE))
+
+
+extern "C"
+{
+  extern const int16_t step_table [258] ;
+}
+
+int32_t BandLimitedWaveform::lookup (int offset)
+{
+  int off = offset >> GUARD_BITS ;
+  int frac = offset & (GUARD-1) ;
+
+  int32_t a, b ;
+  if (off < N/2)   // handle odd symmetry by reflecting table
+  {
+    a = step_table [off+1] ;
+    b = step_table [off+2] ;
+  }
+  else
+  {
+    a = - step_table [N-off] ;
+    b = - step_table [N-off-1] ;
+  }
+  return  BASE_AMPLITUDE + ((frac * b + (GUARD - frac) * a + HALF_GUARD) >> GUARD_BITS) ; // interpolated
+}
+
+void BandLimitedWaveform::insert_step (int offset, bool rising, int i)
+{
+  while (offset <= (N/2-SCALE)<<GUARD_BITS)
+  {
+    if (offset >= 0)
+      cyclic [i & 15] += rising ? lookup (offset) : -lookup (offset) ;
+    offset += SCALE<<GUARD_BITS ;
+    i ++ ;
+  }
+
+  states[newptr].offset = offset ;
+  states[newptr].positive = rising ;
+  newptr = (newptr+1) & PTRMASK ;
+}
+
+int32_t BandLimitedWaveform::process_step (int i)
+{
+  int off = states[i].offset ;
+  bool positive = states[i].positive ;
+
+  int32_t entry = lookup (off) ;
+  off += SCALE<<GUARD_BITS ;
+  states[i].offset = off ;  // update offset in table for next sample
+  if (off >= N<<GUARD_BITS)             // at end of step table we alter dc_offset to extend the step into future
+    dc_offset += positive ? 2*BASE_AMPLITUDE : -2*BASE_AMPLITUDE ;
+
+  return positive ? entry : -entry ;
+}
+
+
+int32_t BandLimitedWaveform::process_active_steps (uint32_t new_phase)
+{
+  int32_t sample = dc_offset ;
+  
+  int step_count = (newptr - delptr) & PTRMASK ;
+  if (step_count > 0)        // for any steps in-flight we sum in table entry and update its state
+  {
+    int i = newptr ;
+    do
+    {
+      i = (i-1) & PTRMASK ;
+      sample += process_step (i) ;
+    } while (i != delptr) ;
+    if (states[delptr].offset >= N<<GUARD_BITS)
+      delptr = (delptr+1) & PTRMASK ;
+  }
+  return sample ;
+}
+
+int32_t BandLimitedWaveform::process_active_steps_saw (uint32_t new_phase)
+{
+  int32_t sample = dc_offset ;
+  
+  int step_count = (newptr - delptr) & PTRMASK ;
+  if (step_count > 0)
+  {
+    int i = newptr ;
+    do
+    {
+      i = (i-1) & PTRMASK ;
+      sample += process_step (i) ;
+    } while (i != delptr) ;
+    if (states[delptr].offset >= N<<GUARD_BITS)
+      delptr = (delptr+1) & PTRMASK ;
+  }
+
+  sample += (int16_t) ((((uint64_t)phase_word * (2*BASE_AMPLITUDE)) >> 32) - BASE_AMPLITUDE) ;  // generate the sloped part of the wave
+  //printf ("phases ,  %x   %x\n", phase_word, new_phase) ;
+
+  if (new_phase < DEG180 && phase_word >= DEG180) // detect wrap around, correct dc offset
+  {
+    //printf ("Trigger dc offset at 0 deg,  %lu   %lu  (%lu)\n", phase_word, new_phase, DEG180) ;
+    dc_offset += 2*BASE_AMPLITUDE ;
+  }
+
+  return sample ;
+}
+
+void BandLimitedWaveform::new_step_check (uint32_t new_phase, int i)
+{
+  if (new_phase >= DEG180 && phase_word < DEG180) // detect rising step
+  {
+    int32_t offset = (int32_t) ((uint64_t) (SCALE<<GUARD_BITS) * (DEG180 - phase_word) / (new_phase - phase_word)) ;
+    if (offset == SCALE<<GUARD_BITS)
+      offset -- ;
+    insert_step (- offset, true, i) ;
+  }
+  if (new_phase < DEG180 && phase_word >= DEG180) // detect wrap around, falling step
+  {
+    int32_t offset = (int32_t) ((uint64_t) (SCALE<<GUARD_BITS) * (- phase_word) / (new_phase - phase_word)) ;
+    if (offset == SCALE<<GUARD_BITS)
+      offset -- ;
+    insert_step (- offset, false, i) ;
+  }
+}
+
+  
+void BandLimitedWaveform::new_step_check_saw (uint32_t new_phase, int i)
+{
+  if (new_phase >= DEG180 && phase_word < DEG180) // detect falling step
+  {
+    int32_t offset = (int32_t) ((uint64_t) (SCALE<<GUARD_BITS) * (DEG180 - phase_word) / (new_phase - phase_word)) ;
+    if (offset == SCALE<<GUARD_BITS)
+      offset -- ;
+    insert_step (- offset, false, i) ;
+  }
+}
+  
+
+int16_t BandLimitedWaveform::generate_sawtooth (uint32_t new_phase, int i)
+{
+  new_step_check_saw (new_phase, i) ;
+  uint16_t val = (int16_t) process_active_steps_saw (new_phase) ;
+  int16_t sample = cyclic [i&15] ;
+  cyclic [i&15] = val ;
+  phase_word = new_phase ;
+  return sample ;
+}
+
+int16_t BandLimitedWaveform::generate_square (uint32_t new_phase, int i)
+{
+  new_step_check (new_phase, i) ;
+  uint16_t val = (int16_t) process_active_steps (new_phase) ;
+  int16_t sample = cyclic [i&15] ;
+  cyclic [i&15] = val ;
+  phase_word = new_phase ;
+  return sample ;
+}
+
+void BandLimitedWaveform::init_sawtooth (uint32_t freq_word)
+{
+  phase_word = 0 ;
+  for (int i = 0 ; i < 2*SUPPORT ; i++)
+    phase_word -= freq_word ;
+  dc_offset = phase_word < DEG180 ? BASE_AMPLITUDE : -BASE_AMPLITUDE ;
+  for (int i = 0 ; i < 2*SUPPORT ; i++)
+  {
+    uint32_t new_phase = phase_word + freq_word ;
+    new_step_check_saw (new_phase, i) ;
+    cyclic [i & 15] = (int16_t) process_active_steps_saw (new_phase) ;
+    phase_word = new_phase ;
+  }
+}
+
+
+void BandLimitedWaveform::init_square (uint32_t freq_word)
+{
+  phase_word = 0 ;
+  for (int i = 0 ; i < 2*SUPPORT ; i++)
+    phase_word -= freq_word ;
+  dc_offset = phase_word < DEG180 ? -BASE_AMPLITUDE : BASE_AMPLITUDE ;
+  
+  for (int i = 0 ; i < 2*SUPPORT ; i++)
+  {
+    uint32_t new_phase = phase_word + freq_word ;
+    new_step_check (new_phase, i) ;
+    cyclic [i & 15] = (int16_t) process_active_steps (new_phase) ;
+    phase_word = new_phase ;
+  }
+}
+
+BandLimitedWaveform::BandLimitedWaveform()
+{
+  newptr = 0 ;
+  delptr = 0 ;
+  dc_offset = BASE_AMPLITUDE ;
+  phase_word = 0 ;
+}

synth_waveform.h

 #define WAVEFORM_SAWTOOTH_REVERSE  6
 #define WAVEFORM_SAMPLE_HOLD       7
 #define WAVEFORM_TRIANGLE_VARIABLE 8
+#define WAVEFORM_BANDLIMIT_SAWTOOTH  9
+#define WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE 10
+#define WAVEFORM_BANDLIMIT_SQUARE 11
+
+
+typedef struct step_state
+{
+  int offset ;
+  bool positive ;
+} step_state ;
+
+
+class BandLimitedWaveform
+{
+public:
+  BandLimitedWaveform (void) ;
+  int16_t generate_sawtooth (uint32_t new_phase, int i) ;
+  int16_t generate_square (uint32_t new_phase, int i) ;
+  void init_sawtooth (uint32_t freq_word) ;
+  void init_square (uint32_t freq_word) ;
+  
+
+private:
+  int32_t lookup (int offset) ;
+  void insert_step (int offset, bool rising, int i) ;
+  int32_t process_step (int i) ;
+  int32_t process_active_steps (uint32_t new_phase) ;
+  int32_t process_active_steps_saw (uint32_t new_phase) ;
+  void new_step_check (uint32_t new_phase, int i) ;
+  void new_step_check_saw (uint32_t new_phase, int i) ;
+
+  
+  uint32_t phase_word ;
+  int32_t dc_offset ;
+  step_state states [32] ; // circular buffer of active steps
+  int newptr ;         // buffer pointers into states, AND'd with PTRMASK to keep in buffer range.
+  int delptr ;
+  int16_t  cyclic[16] ;    // circular buffer of output samples
+};
+
 
 class AudioSynthWaveform : public AudioStream
 {
 	void begin(short t_type) {
 		phase_offset = 0;
 		tone_type = t_type;
+		if (t_type == WAVEFORM_BANDLIMIT_SQUARE)
+		  band_limit_waveform.init_square (phase_increment) ;
+		if (t_type == WAVEFORM_BANDLIMIT_SAWTOOTH || t_type == WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE)
+		  band_limit_waveform.init_sawtooth (phase_increment) ;
 	}
 	void begin(float t_amp, float t_freq, short t_type) {
 		amplitude(t_amp);
 		frequency(t_freq);
 		phase_offset = 0;
-		tone_type = t_type;
+		begin (t_type);
 	}
 	void arbitraryWaveform(const int16_t *data, float maxFreq) {
 		arbdata = data;
 	int16_t  sample; // for WAVEFORM_SAMPLE_HOLD
 	short    tone_type;
 	int16_t  tone_offset;
+        BandLimitedWaveform band_limit_waveform ;
 };
 
 
 	}
 	void begin(short t_type) {
 		tone_type = t_type;
+		if (t_type == WAVEFORM_BANDLIMIT_SQUARE)
+		  band_limit_waveform.init_square (phase_increment) ;
+		if (t_type == WAVEFORM_BANDLIMIT_SAWTOOTH || t_type == WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE)
+		  band_limit_waveform.init_sawtooth (phase_increment) ;
 	}
 	void begin(float t_amp, float t_freq, short t_type) {
 		amplitude(t_amp);
 		frequency(t_freq);
-		tone_type = t_type;
+		begin (t_type) ;
 	}
 	void arbitraryWaveform(const int16_t *data, float maxFreq) {
 		arbdata = data;
 	int16_t  tone_offset;
 	uint8_t  tone_type;
 	uint8_t  modulation_type;
+        BandLimitedWaveform band_limit_waveform ;
 };