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The reverb effect simulates the sound that results from reflections from surrounding walls in a room. To simulate it the guitar signal is delayed several times with different timings, simulating the reflections on the walls.
In this particular effect 3 different delay buffers are used with different timings, the delay time is quite short to give a more realistic impression. The code is 95% similar to the echo code, but instead of using 1 echo buffer we use 3. How to control it:
This code admits plenty of variations, you can change the default delay values (and make them smaller or bigger): uint32_t Delay_Depth1 = 10000; //default starting delay is 100000 is 0.5 sec approx. uint32_t Delay_Depth2 = 5000; //default starting delay is 100000 is 0.25 sec approx. uint32_t Delay_Depth3 = 2500; //default starting delay is 100000 is 0.125 sec approx. You can also play changing the amount of delay added or subtracted when pushing the buttons, making them bigger smaller or different between them: if (Delay_Depth1<DELAY_MAX)Delay_Depth1=Delay_Depth1+5000; //50000 adds 25ms approx. if (Delay_Depth2<DELAY_MAX)Delay_Depth2=Delay_Depth2+5000; //50000 adds 25ms approx. if (Delay_Depth3<DELAY_MAX)Delay_Depth2=Delay_Depth2+5000; //50000 adds 25ms approx. This is the complete code: // CC-by-www.Electrosmash.com Pedal-Pi open-source project.
// reverb audio effect.
#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 Echo_Buffer1[DELAY_MAX];
uint32_t Echo_Buffer2[DELAY_MAX];
uint32_t Echo_Buffer3[DELAY_MAX];
uint32_t DelayCounter1 = 0;
uint32_t DelayCounter2 = 0;
uint32_t DelayCounter3 = 0;
uint32_t Delay_Depth1 = 10000; //default starting delay is 100000 is 0.5 sec approx.
uint32_t Delay_Depth2 = 5000; //default starting delay is 100000 is 0.25 sec approx.
uint32_t Delay_Depth3 = 2500; //default starting delay is 100000 is 0.125 sec approx.
uint32_t input_signal=0;
uint32_t output_signal=0;
uint32_t read_timer;
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;
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 (Delay_Depth1<DELAY_MAX)Delay_Depth1=Delay_Depth1+5000; //50000 adds 25ms approx.
if (Delay_Depth2<DELAY_MAX)Delay_Depth2=Delay_Depth2+5000; //50000 adds 25ms approx.
if (Delay_Depth3<DELAY_MAX)Delay_Depth2=Delay_Depth2+5000; //50000 adds 25ms approx.
}
if (PUSH1_val==0)
{
bcm2835_delay(100); //100ms delay for buttons debouncing.
if (Delay_Depth1>DELAY_MIN)Delay_Depth1=Delay_Depth1-5000;
if (Delay_Depth2<DELAY_MAX)Delay_Depth2=Delay_Depth2+5000; //50000 adds 25ms approx.
if (Delay_Depth3<DELAY_MAX)Delay_Depth3=Delay_Depth3+5000; //50000 adds 25ms approx.
}
}
//**** REVERB EFFECT ***///
//The echo effect is very similar to the echo, but with 3 Echo_Buffers instead of 1 (Echo_Buffer1/2/3)
//Store current readings
//the ">>1" makes the echo to decay, if you want a faster decay change it for ">>2" or ">>3"
Echo_Buffer1[DelayCounter1] = (input_signal + Echo_Buffer1[DelayCounter1])>>1;
Echo_Buffer2[DelayCounter2] = (input_signal + Echo_Buffer2[DelayCounter2])>>1;
Echo_Buffer3[DelayCounter3] = (input_signal + Echo_Buffer3[DelayCounter3])>>1;
DelayCounter1++;
if(DelayCounter1 >= Delay_Depth1) DelayCounter1 = 0;
DelayCounter2++;
if(DelayCounter2 >= Delay_Depth2) DelayCounter2 = 0;
DelayCounter3++;
if(DelayCounter3 >= Delay_Depth3) DelayCounter3 = 0;
output_signal=(input_signal + (Echo_Buffer1[DelayCounter1])+(Echo_Buffer2[DelayCounter2])+(Echo_Buffer3[DelayCounter3]))>>2;
//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;
}
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Last Edit: 4 years 10 months ago by ES_Team.
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