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### Topic: Algorithmic symphonies (Read 1 time)previous topic - next topic

#### Ev0l

##### Oct 29, 2011, 10:26 pm
Inspired by http://countercomplex.blogspot.com/2011/10/algorithmic-symphonies-from-one-line-of.html I decided, hey my Arduino can do that. I have been playing with syntheses on the Arduino for a few months it looked like the perfect little project for a Saturday morning.

I decided easiest is best. Use Fast PWM and throw a lowpass filter on the PWM output to produce the sound. That way I don't have to deal with DACs or R2R ladders and all those pesky little wires. I have used the PWM/lowpass approach for sound generation with a great deal of success in the past.

I sourced the design for the low pass filter from http://interface.khm.de/index.php/lab/experiments/arduino-dds-sinewave-generator/. I did not have the exact values for the inductors but that does not appear to make much of a difference. You could also use a simple RC filter to filter and smooth out the output. RC filters are slightly simpler and if you don't have a couple inductors lying around will produce similar results.

So with out further bloviation here is the source code.

Code: [Select]
`static char out = 255;static int t = 255;static int i = 0;int count = 0;ISR(TIMER1_OVF_vect){    //The timer overflows at 62.5 KHz.   //Algorithmic symphonies calls for 8khz  // Throw a counter in there to slow things down.   // It is also fun to play with the counter :-)  //http://countercomplex.blogspot.com/2011/10/algorithmic-symphonies-from-one-line-of.html  if(count < 7){    count++;    return;  }else{    count = 0;  }  /** The best so far */  out = (char)(((t>>6|t|t>>(t>>3))*10+((t>>11)&7))|(t)*(t>>14)|(t)*(t>>9))              ^(63*(t/16) |(t%13) | (t%15))              ^(16*(t/8));    OCR1A = out;  t++;  }// Configures TIMER1 to fast PWM non inverted mode.// Prescaler set to 1, which means that timer overflows// every 16MHz/256 = 62.5KHzvoid initPWM(void){pinMode(9, OUTPUT);// 8-bit Fast PWM - non inverted PWMTCCR1A= _BV(COM1A1) | _BV(WGM10);// Start timer without prescalerTCCR1B = _BV(CS10) | _BV(WGM12);// Enable overflow interrupt for OCR1ATIMSK1 = _BV(TOIE1);}void setup(void){  initPWM();}void loop(){//Nothing to see here}`

I have attached a sound sample produced by the source code and a low pass filter schematic taken from the above mentioned URL.

I hope you find this as inspiring as I did.

Enjoy,
Will

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