Arduino Vocal Effects Box

This Arduino-powered vocal effects box pitch shifts and distorts incoming audio signals to produce a wide variety of vocal effects. This project is my first experiment with real-time digital signal processing using Arduino. It samples an incoming microphone signal at a rate of about 40kHz, manipulates the audio digitally, and then outputs 8 bit audio at 40kHz. To minimize the amount of computation required by the Arduino, I used a technique called granular synthesis to manipulate the incoming audio signal. Essentially, as audio comes into the Arduino it gets cut up and stored as small (millisecond or microsecond sized) samples called "grains." These grains are then individually manipulated and played back; they may be lengthened or shortened, stretched or compressed, played back in reverse, copied several times, or mixed with other grains. You can hear a (somewhat creepy) audio sample from the effects box below:

Granular synthesis creates a unique type of distortion caused by discontinuities between individual grains in the outgoing signal. Sometimes this distortion creates an effect I can only describe as a "ripping" sound, other times it introduces new frequencies into the audio that were not present before. Here is an example by Aphex Twin, the granular synthesis is especially prominent in the bridge at around 3min in. Another example of granular synthesis, this time applied to vocals for pitch shifting and textural effects, is from Paul Lansky. My favorite thing to do with this effects box is to use subtle pitch shifting to achieve an androgynous vocal sound, I got the idea for the project after listening to copious amounts of Fever Ray this past winter, you can hear how she pitch shifts her voice to sound somewhat masculine at times.

PARTS LIST

(1x) Arduino Uno REV 3 Radioshack 276-128
(7x) 10K Ohm 1/4-Watt Carbon Film Resistor (2 packages) Radioshack #271-1335
(9x) 20K Ohm 1/4-Watt Carbon Film Resistor (2 packages)
(1x) 1K Ohm 1/4-Watt Carbon Film Resistor Radioshack 271-1321
(1x) 50K-Ohm Linear-Taper Potentiometer Radioshack #271-1716
(1x) 10KOhm Audio Control Potentiometer with SPST Switch Radioshack #271-215 (this will be used to control volume and turn the device on/off)
(5x) 0.25" Knurled Knob Radioshack 274-424
(2x) 9V Alkaline Battery Radioshack #23-866
(2x) Heavy-Duty 9V Snap Connectors Radioshack #270-324
(1x) PC Board with Copper Radioshack #276-147
(1x) SPST PC-Mountable Submini Toggle Switch Radioshack #275-645
(2x) Male Header Pins Jameco 103393
(3x) 8 pin socket Radioshack 276-1995
(1x) TL082 Wide Dual JFET Input Op Amp Radioshack 276-1715
(3x) 100K Ohm 1/4-Watt Carbon Film Resistor (1 package) Radioshack 271-1347
(1x) 10uF electrolytic capacitor
(1x) 47nF capacitor
(3x) 0.1uf capacitor Radioshack 55047557
(2x) 1M-Ohm Linear Taper Potentiometer Radioshack 271-211
(1x) 1MOhm logarithmic potentiometer
(1x) 2kOhm 1/4-Watt Carbon Film Resistor
(1x) male header pins Jameco 103393
(1x) 10K-Ohm Linear-Taper Potentiometer Radioshack 271-1715
(1x) DPDT Flatted Metal Lever Toggle Switch Radioshack 275-636
(2x) 1/4" stereo jack Radioshack 274-141 or Radioshack 274-312
(2x) 5mm High-Brightness White LED (1 package) Radioshack 276-017
(2x) 100 ohm 1/4W 5% Carbon Film Resistor Radioshack 271-1311
(2x) TS922IN Dual Op Amp Digikey 497-3049-5-ND (one TS924 would also work, but they are not available on digikey at the moment)

Additional Materials:
22 Gauge Wire Radioshack #278-1224
Solder Radioshack #64-013
sand paper
plywood
wood glue
hot glue
screws

Download Arduino IDE

//63Hz sine wave
//by Amanda Ghassaei 2012
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

//sends 63Hz sine wave to arduino PORTD DAC
float t = 0;

void setup() {
  //set port/pin  mode. see http://www.arduino.cc/en/Reference/PortManipulation for more info
  DDRD = 0xFF;//port d (digital pins 0-7) all outputs
  
  cli();//stop interrupts

  //set timer2 interrupt at 40kHz
  TCCR2A = 0;// set entire TCCR2A register to 0
  TCCR2B = 0;// same for TCCR2B
  TCNT2  = 0;//initialize counter value to 0
  // set compare match register for 40khz increments
  OCR2A = 49;// = (16*10^6) / (8*40000)-1
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);
  // Set CS11 bit for 8 prescaler
  TCCR2B |= (1 << CS11);   
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A);
  
  sei();//allow interrupts
}

ISR(TIMER2_COMPA_vect) {
  //increment t
  t+=1;
  if (t==628){//40kHz/628 =~ 63Hz
    t=0;
  }
}


void loop(){
  //sine wave of frequency ~63Hz
  //send sine values to PORTD between 0 and 255
  PORTD=byte(127+127*sin(t/100));
}

//Simple Audio Out
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/
//July 2012

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

int incomingAudio;

void setup(){
  for (byte i=0;i<8;i++){
    pinMode(i,OUTPUT);//set digital pins 0-7 as outputs
  }
  pinMode(A0,INPUT);
}

void loop(){
  incomingAudio = analogRead(A0);//read input from A0
  incomingAudio = incomingAudio/4;//scale from 10 bit to 8 bit
  PORTD = incomingAudio;//send out DAC
}

//Audio out with 38.5kHz sampling rate
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/
//July 2012

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

void setup(){
  DDRD=0xFF;//set port d (digital pin s0-7) as outputs
  DDRC=0x00;//set all analog pins as inputs
  
  
  //set up continuous sampling of analog pin 0
  
  //clear ADCSRA and ADCSRB registers
  ADCSRA = 0;
  ADCSRB = 0;
  
  ADMUX |= (1 << REFS0); //set reference voltage
  ADMUX |= (1 << ADLAR); //left align the ADC value- so we can read highest 8 bits from ADCH register only
  
  ADCSRA |= (1 << ADPS2) | (1 << ADPS0); //set ADC clock with 32 prescaler- 16mHz/32=500kHz
  ADCSRA |= (1 << ADATE); //enabble auto trigger
  ADCSRA |= (1 << ADEN); //enable ADC
  ADCSRA |= (1 << ADSC); //start ADC measurements
  
}

void loop(){
  PORTD = ADCH;//send 8 bit value from analog pin 0 to DAC
}

//Audio out with 38.5kHz sampling rate and interrupts
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/
//July 2012

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

void setup(){
  DDRD=0xFF;//set port d (digital pin s0-7) as outputs
  DDRC=0x00;//set all analog pins as inputs
  
  cli();//diable interrupts
  
  //set up continuous sampling of analog pin 0
  
  //clear ADCSRA and ADCSRB registers
  ADCSRA = 0;
  ADCSRB = 0;
  
  ADMUX |= (1 << REFS0); //set reference voltage
  ADMUX |= (1 << ADLAR); //left align the ADC value- so we can read highest 8 bits from ADCH register only
  
  ADCSRA |= (1 << ADPS2) | (1 << ADPS0); //set ADC clock with 32 prescaler- 16mHz/32=500kHz
  ADCSRA |= (1 << ADATE); //enabble auto trigger
  ADCSRA |= (1 << ADIE); //enable interrupts when measurement complete
  ADCSRA |= (1 << ADEN); //enable ADC
  ADCSRA |= (1 << ADSC); //start ADC measurements
  
  sei();//enable interrupts
}

ISR(ADC_vect) {//when new ADC value ready
  PORTD = ADCH;//send 8 bit value from analog pin 0 to DAC
}

void loop(){
}

//Half Frequency Playback
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/
//July 2012

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

//audio storage
byte buffer1[1000];
byte buffer2[1000];

byte incomingAudio;//storage variable

int i = 0;//index variable
int iscale = 0;//index variable
int scale = 2;
boolean toggle = 0;
boolean rec = 1;
int limit = 1000;


void setup(){
  DDRD=0xFF;//set port d (digital pin s0-7) as outputs
  DDRC=0x00;//set all analog pins as inputs
  
  cli();//diable interrupts
  
  //set up continuous sampling of analog pin 0
  
  //clear ADCSRA and ADCSRB registers
  ADCSRA=0;
  ADCSRB = 0;
  
  ADMUX |= (1 << REFS0); //set reference voltage
  ADMUX |= (1 << ADLAR); //left align the ADC value- so we can read highest 8 bits from ADCH register only
  
  ADCSRA |= (1 << ADPS2) | (1 << ADPS0); //set ADC clock with 32 prescaler- 16mHz/32=500kHz
  ADCSRA |= (1 << ADATE); //enabble auto trigger
  ADCSRA |= (1 << ADIE); //enable interrupts when measurement complete
  ADCSRA |= (1 << ADEN); //enable ADC
  ADCSRA |= (1 << ADSC); //start ADC measurements
  
  sei();//enable interrupts
}

ISR(ADC_vect) {//when new ADC value ready
  incomingAudio = ADCH;
  if (rec){
    if (toggle){
      buffer1[i] = incomingAudio;//store incoming
      PORTD = buffer2[iscale];//send out DAC
    }
    else{
      buffer2[i] = incomingAudio;//store incoming
      PORTD = buffer1[iscale];//send out DAC
    }
  }
  else{
    if (toggle){
      PORTD = buffer2[iscale];//send out DAC
    }
    else{
      PORTD = buffer1[iscale];//send out DAC
    }
  }
  i += 1;
  iscale = i/scale;
  if (i==limit){
    rec = 0;//stop recording
  }
  if (i == (limit*scale)){
    i = 0;
    iscale = 0;
    toggle^=1;
    rec = 1;
  }
}

void loop(){
}

//Final effects box code
//by Amanda Ghassaei
//https://www.instructables.com/id/Arduino-Vocal-Effects-Box/
//Aug 2012

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
*/

/*
pots:
wet/dry
grain size
pitch shift
*/

//audio storage
byte buffer1[500];
byte buffer2[500];

//buffer recording variables
boolean toggle = 0;
boolean rec = 1;

//pot checking storage
int scale = 20;
int scalePot;
int newScale = scale;
byte multiplier = 0;
int grain = 500;
int grainPot;
int newGrain = grain;
int wetDryPot;
int wet = 16;
int dry = 16-wet;
int newWetDry = wet;

//data retrieval variables
unsigned int i = 0;//index variable
int iscale = 0;//index variable
int iscalerev = grain-1;

//clipping indicator variables
boolean clipping;
int clippingCounter = 5000;

//reverse switch variables
boolean forward = 0;
boolean newForward = forward;


void setup(){
  DDRD=0xFE;//set digital pins 0-7 as outputs
  DDRB=0xFD;//set digital pins 10-13 as outputs, 9 as input
  DDRC=0x00;//set all analog pins as inputs
  
  cli();//diable interrupts
  
  //set up continuous sampling of analog pin 0
  
  //clear ADCSRA and ADCSRB registers
  ADCSRA = 0;
  ADCSRB = 0;
  
  ADMUX = 0;//Clear ADMUX register
  ADMUX |= (1 << REFS0); //set reference voltage
  ADMUX |= (1 << ADLAR); //left align the ADC value- so I can read highest 8 bits from ADCH register only
  //since I'm reading A0, I don't need to specifiy which analog pin I want to read from (0 is default)
  
  ADCSRA |= (1 << ADPS2) | (1 << ADPS0); //set ADC clock with 32 prescaler- 16mHz/32=500kHz
  ADCSRA |= (1 << ADATE); //enabble auto trigger
  ADCSRA |= (1 << ADIE); //enable interrupts when measurement complete
  ADCSRA |= (1 << ADEN); //enable ADC
  ADCSRA |= (1 << ADSC); //start ADC measurements
  
  sei();//enable interrupts
}



ISR(ADC_vect) {//when new ADC value ready
  if (rec){
    if (toggle){
      buffer1[i] = ADCH;//store incoming
      if (ADCH == 0 || ADCH == 1023){//if clipping
        PORTB |= 32;//set pin 13 high
        clippingCounter = 5000;//reset clipping counter
        clipping = 1;//currently clipping
      }
      if (forward){//forward
        PORTD = (wet*int(buffer2[iscale])+dry*int(ADCH))>>4;//send out DAC
      }
      else{//reverse
        PORTD = (wet*int(buffer2[iscalerev])+dry*int(ADCH))>>4;//send out DAC
      }
    }
    else{
      buffer2[i] = ADCH;//store incoming
      if (ADCH == 0 || ADCH == 1023){//if clipping
        PORTB |= 32;//set pin 13 high
        clippingCounter = 5000;//reset clipping counter
        clipping = 1;//currently clipping
      }
      if (forward){
        PORTD = (wet*int(buffer1[iscale])+dry*int(ADCH))>>4;//send out DAC
      }
      else{
        PORTD = (wet*int(buffer1[iscalerev])+dry*int(ADCH))>>4;//send out DAC
      }
    }
  }
  else{
    if (toggle){
      if (forward){
        PORTD = (wet*int(buffer2[iscale])+dry*int(ADCH))>>4;//send out DAC
      }
      else{
        PORTD = (wet*int(buffer2[iscalerev])+dry*int(ADCH))>>4;//send out DAC
      }
    }
    else{
      if (forward){
        PORTD = (wet*int(buffer1[iscale])+dry*int(ADCH))>>4;//send out DAC
      }
      else{
        PORTD = (wet*int(buffer1[iscalerev])+dry*int(ADCH))>>4;//send out DAC
      }
    }
  }
  i++;//increment i
  iscale = i*10/scale-grain*multiplier;
  iscalerev = grain-iscale-1;
  if (i==grain){
    rec = 0;//stop recording
  }
  if (i>=(grain*scale/10)){
    if (scale<10){
      if (i==grain){
        i = 0;
        iscale = 0;
        iscalerev = grain-1;
        forward = newForward;//update direction
        scale = newScale;//update scale
        grain = newGrain;//update grain
        dry = newWetDry;//update wet dry
        wet = 16-dry;
        toggle ^= 1;//try removing this
        rec = 1;
        multiplier = 0;
      }
      else if (iscale>=grain){
        iscale = 0;
        iscalerev = grain-1;
        multiplier++;
      }
    }
    else{
      i = 0;
      iscale = 0;
      iscalerev = grain-1;
      forward = newForward;//update direction
      scale = newScale;//update scale
      grain = newGrain;//update grain
      dry = newWetDry;//update wet dry
      wet = 16-dry;
      toggle ^= 1;//try removing this
      rec = 1;
      multiplier = 0;
    }
  }
  if (clipping){
    clippingCounter--;//decrement clipping counter
  }
}

void checkScale(){
  PORTB &= 251;//set pin 10 low
  scalePot = 0;
  while(digitalRead(10)){
    scalePot++;
  }
  newScale = scalePot+2;
}

void checkGrainSize(){
  PORTB &= 247;//set pin 11 low
  grainPot = 0;
  while(digitalRead(11)){
    grainPot++;
  }
  if (grainPot < 1){
    grainPot = 1;
  }
  else if (grainPot > 20){
    grainPot = 20;
  }
  newGrain = grainPot*25;
}

void checkWetDry(){
  PORTB &= 239;//set pin 12 low
  wetDryPot = 0;
  while(digitalRead(12)){
    wetDryPot++;//from 0 to ~185
  }
  if (wetDryPot < 10){
    wetDryPot = 0;
  }
  else if (wetDryPot > 160){
    wetDryPot = 160;
  }
  newWetDry = wetDryPot/10;//scale down to 16
}

void checkRev(){//check reverse switch
  if (digitalRead(9)){
    newForward = 1;
  }
  else{
    newForward = 0;
  }
}

void loop(){
  if (clipping){//if currently clipping
    if (clippingCounter<=0){//if enough time has passed since clipping
      clipping = 0;//not currently clipping
      PORTB &= 223;//turn off clipping led indicator (pin 13)
    }
  }
  DDRB=0xFD;//set pins 10-12 as outputs
  PORTB |= 28;//set pins 10-12 high
  delay(1);//wait for capacitor to discharge
  checkRev();//check reverse switch
  DDRB= 0xE1;//set pins 10-12 as inputs
  checkScale();
  checkGrainSize();
  checkWetDry();
}