Simple polyphonic synth with just arduino

Video: http://www.youtube.com/watch?v=wJZVMu78T9g

So, i thought it might be possible to generate more than one tone at a time using Arduino. The idea and the outcome is relatively simple, yet i still quite like the character of the sound.

The modulo (with symbol %) of two numbers means that the outcome equals the remainder when the left number is divided by the right number. So:

5 % 2 = 1
and
5 % 3 = 2

and so on.

Consider that we have a counter variable, 'c' that increments with every loop of code. By performing the modulo operation on 'c', it is possible to creates loops within the larger loop that will occur 'alongside' (concurrently with) the main loop.

So, let us set up a loop with a length of eight iterations and add a single modulo function in relation to 'c' (using the variable 'a'):

for(int c = 0; c < 8; c++) {

a = c % 3;

}

So, when c = 0, 1, 2, 3, 4, 5, 6, 7, a = 0, 1, 2, 0, 1, 2, 0, 1 respectively.

The synthesis relies on creating a long loop (based on the integer i). Then, four oscillators are created and controlled by setting digital output pins d2 to d5 based on smaller, concurrent modulo loops.

For the first half of the modulo loop, the pin will be set low. For the second half, it will be held high. The length of the modulo loop (and therefore the frequency of the oscillator in question) is controlled by one of four pots (one for each oscillator).



Code:

/* Very basic polyphonic synth with Arduino

by Sebastian Tomczak



5 February 2008

*/

byte state;

byte mod[] = {

0, 0, 0, 0};

void setup() {

DDRD = DDRD | B11111100;

DDRB = DDRB | B00000000;

}

void loop() {

for(int i = 0; i < 32767; i++) {

for(int j = 0; j < 4; j++) {

state = 0;

mod[j] = analogRead(j) >> 2 & B11111110;

mod[j] = i % mod[j] / (mod[j] / 2);

state = state + mod[j];

state = state << 1;

PORTD = state << 2;

}

}

}