Welcome, Guest
Username: Password: Remember me

TOPIC: Bit-Crusher Guitar Effect Pedal.

Bit-Crusher Guitar Effect Pedal. 2 years 5 months ago #869

  • ES_Team
  • ES_Team's Avatar
  • OFFLINE
  • Administrator
  • Posts: 23
  • Thank you received: 2
  • Karma: 0
From Wikipedia:
"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 high distorted sound. The push-buttons makes the effect more or less aggressive.

How to control it:
  • Push-Button 1 (left): softer bit-crushing.
  • Push-Button 2 (right): harder bit-crushing.
  • Led: ON when the effect is activated.
  • Toggle Button: not used.
  • Foot-Switch: activate/deactivate the effect.

I have to say that this effect is very very very aggressive, it goes from 0 distortion to too much distortion in just one push. It needs some refinement, maybe adding the original signal after the crushing or making it more mild... but as concept here it is:
// CC-by-www.Electrosmash.com open-source project.
 
#include <bcm2835.h>
#include <stdio.h>

// Define Input Pins
#define PUSH1 			RPI_GPIO_P1_08  	//GPIO14
#define PUSH2 			RPI_V2_GPIO_P1_38  	//GPIO20 
#define TOGGLE_SWITCH 	RPI_V2_GPIO_P1_32 	//GPIO12
#define FOOT_SWITCH 	RPI_GPIO_P1_10 		//GPIO15
#define LED   			RPI_V2_GPIO_P1_36 	//GPIO16

uint32_t read_timer=0;
uint32_t input_signal=0;
uint32_t output_signal=0;
uint32_t bitcrushing_value=1; // 1 bit crushed by default.
 
uint8_t FOOT_SWITCH_val;
uint8_t TOGGLE_SWITCH_val;
uint8_t PUSH1_val;
uint8_t PUSH2_val;
 
int main(int argc, char **argv)
{
    // Start the BCM2835 Library to access GPIO.
    if (!bcm2835_init())
    { printf("bcm2835_init failed. Are you running as root??\n");
      return 1;}
	// Start the SPI BUS.
	if (!bcm2835_spi_begin())
    {printf("bcm2835_spi_begin failed. Are you running as root??\n");
      return 1;}
 
	//define PWM	
    bcm2835_gpio_fsel(18,BCM2835_GPIO_FSEL_ALT5 ); //PWM0 signal on GPIO18    
    bcm2835_gpio_fsel(13,BCM2835_GPIO_FSEL_ALT0 ); //PWM1 signal on GPIO13    
	bcm2835_pwm_set_clock(2); // Max clk frequency (19.2MHz/2 = 9.6MHz)
    bcm2835_pwm_set_mode(0,1 , 1); //channel 0, markspace mode, PWM enabled. 
	bcm2835_pwm_set_range(0,64);   //channel 0, 64 is max range (6bits): 9.6MHz/64=150KHz switching PWM freq.
    bcm2835_pwm_set_mode(1, 1, 1); //channel 1, markspace mode, PWM enabled.
	bcm2835_pwm_set_range(1,64);   //channel 0, 64 is max range (6bits): 9.6MHz/64=150KHz switching PWM freq.
 
	//define SPI bus configuration
    bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_MSBFIRST);      // The default
    bcm2835_spi_setDataMode(BCM2835_SPI_MODE0);                   // The default
    bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_64); 	  // 4MHz clock with _64 
    bcm2835_spi_chipSelect(BCM2835_SPI_CS0);                      // The default
    bcm2835_spi_setChipSelectPolarity(BCM2835_SPI_CS0, LOW);      // the default
 
   	uint8_t mosi[10] = { 0x01, 0x00, 0x00 }; //12 bit ADC read 0x08 ch0, - 0c for ch1 
	uint8_t miso[10] = { 0 };
 
    //Define GPIO pins configuration
    bcm2835_gpio_fsel(PUSH1, BCM2835_GPIO_FSEL_INPT); 			//PUSH1 button as input
	bcm2835_gpio_fsel(PUSH2, BCM2835_GPIO_FSEL_INPT); 			//PUSH2 button as input
	bcm2835_gpio_fsel(TOGGLE_SWITCH, BCM2835_GPIO_FSEL_INPT);	//TOGGLE_SWITCH as input
	bcm2835_gpio_fsel(FOOT_SWITCH, BCM2835_GPIO_FSEL_INPT); 	//FOOT_SWITCH as input
	bcm2835_gpio_fsel(LED, BCM2835_GPIO_FSEL_OUTP);				//LED as output
 
    bcm2835_gpio_set_pud(PUSH1, BCM2835_GPIO_PUD_UP);           //PUSH1 pull-up enabled   
	bcm2835_gpio_set_pud(PUSH2, BCM2835_GPIO_PUD_UP);           //PUSH2 pull-up enabled 
	bcm2835_gpio_set_pud(TOGGLE_SWITCH, BCM2835_GPIO_PUD_UP);   //TOGGLE_SWITCH pull-up enabled 
	bcm2835_gpio_set_pud(FOOT_SWITCH, BCM2835_GPIO_PUD_UP);     //FOOT_SWITCH pull-up enabled 
 
	while(1) //Main Loop
	{
	//read 12 bits ADC
    bcm2835_spi_transfernb(mosi, miso, 3);
    input_signal = miso[2] + ((miso[1] & 0x0F) << 8); 
 
	//Read the PUSH buttons every 50000 times (0.25s) to save resources.
	read_timer++;
	if (read_timer==50000)
	{
	read_timer=0;
	uint8_t PUSH1_val = bcm2835_gpio_lev(PUSH1);
	uint8_t PUSH2_val = bcm2835_gpio_lev(PUSH2);
    TOGGLE_SWITCH_val = bcm2835_gpio_lev(TOGGLE_SWITCH);
	uint8_t FOOT_SWITCH_val = bcm2835_gpio_lev(FOOT_SWITCH);
	//light the effect when the footswitch is activated.
	bcm2835_gpio_write(LED,!FOOT_SWITCH_val); 
 
	//update booster_value when the PUSH1 or 2 buttons are pushed.
	if (PUSH2_val==0)
		{ bcm2835_delay(100); //100ms delay for buttons debouncing
         if (bitcrushing_value<12) bitcrushing_value++;
		}
		else if (PUSH1_val==0) 
			{bcm2835_delay(100); //100ms delay for buttons debouncing.
			if (bitcrushing_value>0) bitcrushing_value--;
			}
	}
 
	//**** BITCRUSHING EFFECT ***///
	//The input_signal gets a  a bit shift operation "<<" 
	//The number of bits shifted are defined by bitcrushing_value
    output_signal= input_signal<<bitcrushing_value;
 
	//generate output PWM signal 6 bits
    bcm2835_pwm_set_data(1,output_signal & 0x3F);
    bcm2835_pwm_set_data(0,output_signal >> 6);
    }
 
	//close all and exit
	bcm2835_spi_end();
    bcm2835_close();
    return 0;
}


File Attachment:

File Name: bitcrusher.zip
File Size: 2 KB
Last Edit: 2 years 4 months ago by ES_Team.
The administrator has disabled public write access.
Time to create page: 0.303 seconds
Powered by Kunena Forum
Joomla SEF URLs by Artio