Fix various issues with bandlimit pulse after testing with changing/modulating pulse width and freq, also invert phase of square and pulse to match existing tone types

synth_waveform.cpp

@@ -486,6 +486,7 @@ void AudioSynthWaveformModulated::update(void)
 
 #define BASE_AMPLITUDE 0x6000  // 0x7fff won't work due to Gibb's phenomenon, so use 3/4 of full range.
 
+#define DEG90 0x40000000u
 #define DEG180 0x80000000u
 
 #define PHASE_SCALE (0x100000000L / (2 * BASE_AMPLITUDE))
@@ -578,19 +579,27 @@ int32_t BandLimitedWaveform::process_active_steps_saw (uint32_t new_phase)
 
 void BandLimitedWaveform::new_step_check_pulse (uint32_t new_phase, uint32_t pulse_width, int i)
 {
-  if (new_phase >= pulse_width && phase_word < pulse_width) // detect rising step
+  if (new_phase >= pulse_width && phase_word < pulse_width) // detect falling step
   {
     int32_t offset = (int32_t) ((uint64_t) (SCALE<<GUARD_BITS) * (pulse_width - phase_word) / (new_phase - phase_word)) ;
     if (offset == SCALE<<GUARD_BITS)
       offset -- ;
-    insert_step (- offset, true, i) ;
+    if (pulse_state) // guard against two falling steps in a row (if pulse width changing for instance)
+    {
+      insert_step (- offset, false, i) ;
+      pulse_state = false ;
+    }
   }
-  if (new_phase < pulse_width && phase_word >= pulse_width) // detect wrap around, falling step
+  if (new_phase < pulse_width && phase_word >= pulse_width) // detect wrap around, rising 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) ;
+    if (!pulse_state) // guard against two rising steps in a row (if pulse width changing for instance)
+    {
+      insert_step (- offset, true, i) ;
+      pulse_state = true ;
+    }
   }
 }
 
@@ -668,7 +677,16 @@ void BandLimitedWaveform::init_pulse (uint32_t freq_word, uint32_t pulse_width)
   for (int i = 0 ; i < 2*SUPPORT ; i++)
     phase_word -= freq_word ;
 
-  dc_offset = phase_word < DEG180 ? -BASE_AMPLITUDE : BASE_AMPLITUDE ;
+  if (phase_word < DEG90)
+  {
+    dc_offset = BASE_AMPLITUDE ;
+    pulse_state = true ;
+  }
+  else
+  {
+    dc_offset = -BASE_AMPLITUDE ;
+    pulse_state = false ;
+  }
   
   for (int i = 0 ; i < 2*SUPPORT ; i++)
   {

synth_waveform.h

@@ -49,7 +49,7 @@ extern const int16_t AudioWaveformSine[257];
 #define WAVEFORM_BANDLIMIT_SAWTOOTH  9
 #define WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE 10
 #define WAVEFORM_BANDLIMIT_SQUARE 11
-#define WAVEFORM_BANDLIMIT_PULSE 12
+#define WAVEFORM_BANDLIMIT_PULSE  12
 
 
 typedef struct step_state
@@ -87,6 +87,7 @@ private:
   int newptr ;         // buffer pointers into states, AND'd with PTRMASK to keep in buffer range.
   int delptr ;
   int32_t  cyclic[16] ;    // circular buffer of output samples
+  bool pulse_state ;
 };
 
 
@@ -108,6 +109,7 @@ public:
 		}
 		phase_increment = freq * (4294967296.0 / AUDIO_SAMPLE_RATE_EXACT);
 		if (phase_increment > 0x7FFE0000u) phase_increment = 0x7FFE0000;
+		ensure_pulse_width_ok () ;
 	}
 	void phase(float angle) {
 		if (angle < 0.0) {
@@ -141,13 +143,7 @@ public:
 			n = 1.0;
 		}
 		pulse_width = n * 4294967296.0;
-		if (tone_type == WAVEFORM_BANDLIMIT_PULSE)
-		{
-		  if (pulse_width < phase_increment)  // ensure pulse never narrow enough to glitch out of existence.
-		    pulse_width = phase_increment ;
-		  else if (pulse_width > -phase_increment)
-		    pulse_width = -phase_increment;
-		}
+		ensure_pulse_width_ok () ;
 	}
 	void begin(short t_type) {
 		phase_offset = 0;
@@ -156,10 +152,7 @@ public:
 		  band_limit_waveform.init_square (phase_increment) ;
 		else if (t_type == WAVEFORM_BANDLIMIT_PULSE)
 		{
-		  if (pulse_width < phase_increment)  // ensure pulse never narrow enough to glitch out of existence.
-		    pulse_width = phase_increment ;
-		  else if (pulse_width > -phase_increment)
-		    pulse_width = -phase_increment;
+		  ensure_pulse_width_ok () ;
 		  band_limit_waveform.init_pulse (phase_increment, pulse_width) ;
 		}
 		else if (t_type == WAVEFORM_BANDLIMIT_SAWTOOTH || t_type == WAVEFORM_BANDLIMIT_SAWTOOTH_REVERSE)
@@ -177,6 +170,16 @@ public:
 	virtual void update(void);
 
 private:
+	void ensure_pulse_width_ok()
+	{
+		if (tone_type == WAVEFORM_BANDLIMIT_PULSE)
+		{
+		  if (pulse_width < phase_increment)  // ensure pulse never narrow enough to glitch out of existence.
+		    pulse_width = phase_increment ;
+		  else if (pulse_width > -phase_increment)
+		    pulse_width = -phase_increment;
+		}
+	}
 	uint32_t phase_accumulator;
 	uint32_t phase_increment;
 	uint32_t phase_offset;