Serial obj not connecting through to serial COM port to accept data from Arduino

Sam - Thanks, this is very helpful and clarifying! I'm familiar with OSC, so would be great to use that. By Processing, do you mean this thing https://processing.org/?

Source Audio - I actually don't know very much about coding yet. How do I send a "dtr 1" message to the baord? Somewhere in setup(), maybe before serial.begin()? And would it be something like serial.write() or serial.print() function? This is the short tutorial sketch I'm using. Thanks so much for your help!

long randomvalue = 0; // random value
long countervalue = 0; // counter value
int serialvalue; // value for serial input
int started = 0; // flag for whether we've received serial yet

void setup()
{
  Serial.begin(9600); // open the arduino serial port
}


void loop()
{
  if(Serial.available()) // check to see if there's serial data in the buffer
  {
    serialvalue = Serial.read(); // read a byte of serial data
    started = 1; // set the started flag to on
  }
  if(started) { // loop once serial data has been received
    randomvalue = random(1000); // pick a new random number
    Serial.print(countervalue); // print the counter
    Serial.print(" "); // print a space
    Serial.print(randomvalue); // print the random value
    Serial.print(" "); // print a space
    Serial.print(serialvalue); // echo the received serial value
    Serial.println(); // print a line-feed
    countervalue = (countervalue+1)%1000; // increment the counter
    delay(100); // pause
  }
}