This effect generates an octaved signal which is created from the original guitar input signal by halving (octave-down) or doubling (octave-up) its frequency.
To implement the effect, one buffer is used to store the current signal. The buffer is written at a "constant speed" but read with different speed: half (octave-down) or double speed (octave-up).
How to control it:
- Push-Button 1 (left): press for Octave down.
- Push-Button 2 (right): press for Octave up.
- Led: ON when the effect is activated
- Toggle Button: not used.
- Foot-Switch: activate/deactivate the effect.
The most important parameter is the Delay_Depth variable, try making it bigger or smaller to your taste (it makes the recording buffer bigger or smaller)
uint32_t Delay_Depth = 50000; //default starting delay is 100000 is 0.25 sec approx.
Here is the code:
// CC-by-www.Electrosmash.com Pedal-Pi open-source project.
// Octaver audio effect.
// Effect upgraded by Matomick
#include <stdio.h>
#include <bcm2835.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
//Define Delay Effect parameters MAX_DELAY 800000 is 4 seconds approx.
#define DELAY_MAX 800000
#define DELAY_MIN 0
uint32_t Delay_Buffer[DELAY_MAX];
uint32_t DelayWrite = 0;
uint32_t DelayRead = 0;
uint32_t octaver_value = 1;
uint32_t Delay_Depth = 50000; //default starting delay is 100000 is 0.25 sec approx.
uint32_t input_signal=0;
uint32_t output_signal=0;
uint32_t read_timer, delay, divider;
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){
//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;
PUSH1_val = bcm2835_gpio_lev(PUSH1);
PUSH2_val = bcm2835_gpio_lev(PUSH2);
TOGGLE_SWITCH_val = bcm2835_gpio_lev(TOGGLE_SWITCH);
FOOT_SWITCH_val = bcm2835_gpio_lev(FOOT_SWITCH);
//light the effect when the footswitch is activated.
bcm2835_gpio_write(LED,!FOOT_SWITCH_val);
//update volume variable when the PUSH buttons are pushed.
if (PUSH2_val==0){
bcm2835_delay(100); //100ms delay for buttons debouncing.
if (octaver_value<2)octaver_value++;
}
if (PUSH1_val==0){
bcm2835_delay(100); //100ms delay for buttons debouncing.
if (octaver_value>0)octaver_value--;
}
}
//**** OCTAVER EFFECT ***///
//save current reading
Delay_Buffer[DelayWrite] = input_signal;
//Increase/reset delay counter.
DelayWrite++;
if(DelayWrite >= Delay_Depth) DelayWrite = 0;
output_signal = Delay_Buffer[DelayRead];
if (octaver_value == 2) DelayRead = DelayRead + 2;
if (octaver_value == 1) DelayRead = DelayRead + 1;
if (octaver_value == 0){
divider++;
if (divider>=2)
{
DelayRead = DelayRead + 1;
divider=0;
}
}
if(DelayRead >= Delay_Depth) DelayRead = 0;
//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;
}
