Updated comments

Karplus_Strong/Karplus_Strong.ino

@@ -0,0 +1,62 @@
+// Very basic Karplus-Strong 
+
+// based on this explanation http://sites.music.columbia.edu/cmc/MusicAndComputers/chapter4/04_09.php
+
+
+#include <Adafruit_MCP4728.h>
+#include <Wire.h>
+
+Adafruit_MCP4728 mcp;
+
+#define nsamp 128
+#define dacmax 256
+
+unsigned int phase;
+unsigned int repeats;
+
+
+void setup() {
+
+  Serial.begin(115200);
+
+  if (!mcp.begin(0x64)) {
+    while (1) {
+      delay(100);
+    }
+  }
+
+//  mcp.setSpeed(400000L);
+//  mcp.setSpeed(800000L);
+  mcp.setSpeed(800000L);
+
+  phase=0;
+  pluck();
+}
+
+byte waveform[nsamp];
+void pluck(){
+  Serial.println("pluck");
+  for (int i=0; i<nsamp; ++i){
+    waveform[i]=random(256);
+  }
+}
+
+void loop() {
+  byte s1, s2;
+  int p0 = phase;
+  s1 = waveform[phase];
+  phase += 1;
+  if( phase > nsamp ) {
+    phase = 0;
+    repeats += 1;
+  }
+  s2 = waveform[phase];
+  waveform[p0] = ( s1 & s2 ) + ((s1 ^ s2) >> 1);
+  mcp.fastWrite(s1 << 4, 0, 0, 0);
+  if( repeats > 100 ) {
+    pluck();
+    repeats = 0;
+
+  }
+}
+

waveforms/waveforms.ino

@@ -7,44 +7,39 @@
 
 Adafruit_MCP4728 mcp;
 
-#define nsamp 256
+#define nsamp 32
 #define dacmax 256
 
-const byte nclk=42; //number of clock cycles of the loop
-long int freq; //frequency in mHz
+const byte nclk = 200; // a guess
+long int freq; //frequency in Hz
 long unsigned int phase;
 long unsigned int phase_inc;
 
 void setup() {
-  //TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt
- 
-  //Wire.setClock(1400000L); // wooooo
+//  TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt
+
   Serial.begin(115200);
-  while (!Serial)
-    delay(10); // will pause Zero, Leonardo, etc until serial console opens
 
-
-  // Try to initialize!
   if (!mcp.begin(0x64)) {
-    Serial.println("Failed to find MCP4728 chip");
     while (1) {
-      delay(10);
+      delay(100);
     }
-  } else {
-    Serial.println("Adafruit MCP4728 initialised");
   }
 
+//  mcp.setSpeed(400000L);
+//  mcp.setSpeed(800000L);
+  mcp.setSpeed(800000L);
 
-  freq=660;
+  freq=440;
   phase=0;
   calc_phase_inc();
-  //phase_inc = 1;
 
   setwave();
 }
 
 const float pi=3.14159265;
 byte waveform[nsamp];
+byte phaseb = 0;
 void setwave(){
   for (int isamp=0; isamp<nsamp; ++isamp){
     float phip=(isamp+0.5)/nsamp;
@@ -52,10 +47,10 @@ void setwave(){
     int val=0;
 
     //saw
-    val = dacmax * isamp / nsamp;
+  //val = dacmax * isamp / nsamp;
     //val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1;
         //sine
-    //val=(sin(phi)+1.0)*dacmax/2;
+    val=(sin(phi)+1.0)*dacmax/2;
     //val=((sin(phi)+0.333*sin(3*phi))/0.943+1)*dacmax/2;
 
     val=max(val,0);
@@ -65,19 +60,19 @@ void setwave(){
 }
 
 
-//calculate the phase increment. 2^32/16E6=268.435456
+//calculate the phase increment. 
 void calc_phase_inc(){
-  phase_inc=0.268435456*nclk*freq;
-  Serial.println("phase inc");
+  // by measurement, 2^27 is about 138Hz (C below middle C)
+  // 2^27 / 138 = 972592.231884058
+  phase_inc = freq * 975592.231884058;
   Serial.println(phase_inc);
 }
 
-//regular running: generate waves
+
+
 void loop() {
-  //phase+=900;
-  //int redphase = phase >> 24;
-  phase += analogRead(A0);
-  int redphase = phase % nsamp;
-  mcp.fastWrite(waveform[redphase] << 4, 0, 0,   0);
+  phase += phase_inc;
+  int redphase = phase >> 27;
+  mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0);
 }