A Bitcrusher is a lo-fi (low fidelity) digital audio effect, which produces a distortion by the reduction of the resolution or bandwidth of digital audio data. The resulting quantization noise may produce a “warmer” sound impression, or a harsh one, depending on the amount of reduction.
This effect moves the bits of the input signal using the << operation, creating a highly distorted sound. The push-buttons makes the effect more or less aggressive by shifting one, two, or more bits.
This is the complete code:
// www.Electrosmash.com/pedalshield-mega
/* pedalshield_mega_bit_crusher.ino reads the ADC and shift the bits creating a high distorted sound
* pressing the pushbutton_1 or 2 turns the bit shift harder or softer..
*/
#include "U8glib.h"
U8GLIB_SH1106_128X64 u8g(U8G_I2C_OPT_NO_ACK); // Display which does not send ACK
//defining hardware resources.
#define LED 13
#define FOOTSWITCH 12
#define TOGGLE 2
#define PUSHBUTTON_1 A5
#define PUSHBUTTON_2 A4
//defining the output PWM parameters
#define PWM_FREQ 0x00FF // pwm frequency - 31.3KHz
#define PWM_MODE 0 // Fast (1) or Phase Correct (0)
#define PWM_QTY 2 // 2 PWMs in parallel
//other variables
int input, bit_crush_variable=0;
int counter=0;
unsigned int ADC_low, ADC_high;
void setup() {
//setup IO
pinMode(FOOTSWITCH, INPUT_PULLUP);
pinMode(TOGGLE, INPUT_PULLUP);
pinMode(PUSHBUTTON_1, INPUT_PULLUP);
pinMode(PUSHBUTTON_2, INPUT_PULLUP);
pinMode(LED, OUTPUT);
pinMode(6, OUTPUT); //PWM0 as output
pinMode(7, OUTPUT); //PWM1 as output
// setup ADC
ADMUX = 0x60; // left adjust, adc0, internal vcc
ADCSRA = 0xe5; // turn on adc, ck/32, auto trigger
ADCSRB = 0x00; //free running mode
DIDR0 = 0x01; // turn off digital inputs for adc0
// setup PWM
TCCR4A = (((PWM_QTY - 1) << 5) | 0x80 | (PWM_MODE << 1)); //
TCCR4B = ((PWM_MODE << 3) | 0x11); // ck/1
TIMSK4 = 0x20; // interrupt on capture interrupt
ICR4H = (PWM_FREQ >> 8);
ICR4L = (PWM_FREQ & 0xff);
DDRB |= ((PWM_QTY << 1) | 0x02); // turn on outputs
sei(); // turn on interrupts - not really necessary with arduino
}
void loop()
{
//Turn on the LED and write the OLED if the effect is ON.
if (digitalRead(FOOTSWITCH))
{
digitalWrite(LED, HIGH); //light the LED
u8g.firstPage();
do {
u8g.setFont(u8g_font_helvR12r);
u8g.drawStr( 0, 25, " BIT CRUSHER");
u8g.setPrintPos(50, 60);
u8g.setFont(u8g_font_helvR24r);
u8g.print(bit_crush_variable);
u8g.setFont(u8g_font_helvR12r);
u8g.print(" Bits");
} while( u8g.nextPage() );
}
else
{
digitalWrite(LED, LOW); // switch-off the LED
u8g.firstPage();
do {
u8g.setFont(u8g_font_helvR24r);
u8g.drawStr( 0, 30, "EFFECT");
u8g.drawStr( 0, 60, " OFF ");
} while( u8g.nextPage() );
}
}
ISR(TIMER4_CAPT_vect)
{
// get ADC data
ADC_low = ADCL; // you need to fetch the low byte first
ADC_high = ADCH;
//construct the input sumple summing the ADC low and high byte.
input = ((ADC_high << 8) | ADC_low) + 0x8000; // make a signed 16b value
//// All the Digital Signal Processing happens here: ////
counter++; //to save resources, the pushbuttons are checked every 10000 times.
if(counter==10000)
{
counter=0;
if (!digitalRead(PUSHBUTTON_2)) {
if (bit_crush_variable<16)bit_crush_variable=bit_crush_variable+1; //increase the number of crushed bits
digitalWrite(LED, LOW); //blinks the led
}
if (!digitalRead(PUSHBUTTON_1)) {
if (bit_crush_variable>0)bit_crush_variable=bit_crush_variable-1; //decrease the number of crushed bits
digitalWrite(LED, LOW); //blinks the led
}
}
//The bit_crush_variable goes from 0 to 16 and the input signal is crushed in the next instruction:
input = input<<bit_crush_variable;
//write the PWM signal
OCR4AL = ((input + 0x8000) >> 8); // convert to unsigned, send out high byte
OCR4BL = input; // send out low byte
}