Vox Imperium: Stormtrooper Voice Changer

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Contributors: Shawn Hymel
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The Code

Create a new Arduino sketch and copy in the code:

language:c
#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code
AudioInputAnalog         adc1;           //xy=255,182
AudioFilterBiquad        biquad1;        //xy=394,182
AudioPlaySerialflashRaw  playFlashRaw1;  //xy=535,319
AudioFilterStateVariable filter1;        //xy=558,189
AudioAnalyzePeak         peak1;          //xy=559,255
AudioMixer4              mixer1;         //xy=710,196
AudioOutputAnalog        dac1;           //xy=844,196
AudioConnection          patchCord1(adc1, biquad1);
AudioConnection          patchCord2(biquad1, 0, filter1, 0);
AudioConnection          patchCord3(biquad1, peak1);
AudioConnection          patchCord4(playFlashRaw1, 0, mixer1, 2);
AudioConnection          patchCord5(filter1, 0, mixer1, 0);
AudioConnection          patchCord6(filter1, 2, mixer1, 1);
AudioConnection          patchCord7(mixer1, dac1);
// GUItool: end automatically generated code

// Parameters
const bool DEBUG = false;
const bool BEGIN_CLICK = true;  // Play click on voice start
const bool END_SOUND = true;    // Play click/burst on voice end
const bool FEEDBACK_SUPPRESSION = false;  // Enables input filter
const unsigned int LOWPASS_CUTOFF = 2200; // Hz
const unsigned int CROSSOVER_FREQ = 2000; // Filter center freq
const float BASS_GAIN_ON = 0.01;
const float BASS_GAIN_OFF = 0.0;
const float TREBLE_GAIN_ON = 0.25;    // Voice output volume
const float TREBLE_GAIN_OFF = 0.0;
const float SFX_GAIN = 0.5;           // Sound clip volume
const float SQUELCH_CUTOFF = 0.10;    // Voice threshold
const int HYSTERESIS_TIME_ON = 20;    // Milliseconds
const int HYSTERESIS_TIME_OFF = 400;  // Milliseconds

// Pins
const int FLASH_CS = 6;               // Serial flash chip select
const int AMP_ENABLE = 5;             // Amplifier enable pin

// On/Off state machine states
typedef enum volState {
  QUIET,
  QUIET_TO_LOUD,
  LOUD,
  LOUD_TO_QUIET,
} VolState;

// Global variables
elapsedMillis fps; // Sample peak only if we have available cycles
VolState state = QUIET;
unsigned long timer;

void setup() {

  if ( DEBUG ) {
    Serial.begin(9600);
  }

  // Initialize amplifier
  AudioMemory(20);
  dac1.analogReference(EXTERNAL); // much louder!
  delay(50);                      // time for DAC voltage stable
  pinMode(AMP_ENABLE, OUTPUT);

  // wait up to 10 seconds for Arduino Serial Monitor
  unsigned long startMillis = millis();
  if ( DEBUG ) {
    while ( !Serial && ( millis() - startMillis < 10000 ) );
  }

  // Butterworth lowpass filter (reduces audio feedback)
  if ( FEEDBACK_SUPPRESSION ) {
    biquad1.setLowpass(0, LOWPASS_CUTOFF, 0.707);
  } else {
    biquad1.setLowpass(0, 8000, 0.707);
  }

  // Configure the State Variable filter
  filter1.frequency(CROSSOVER_FREQ);
  filter1.resonance(0.707);

  // Adjust gain into the mixer
  mixer1.gain(0, BASS_GAIN_OFF);
  mixer1.gain(1, TREBLE_GAIN_OFF);
  mixer1.gain(2, SFX_GAIN);

  // Initialize serial flash
  if ( !SerialFlash.begin(FLASH_CS) ) {
    if ( DEBUG ) {
      Serial.println( "Unable to access SPI Flash chip" );
    }
  }

  // Use the time since boot as a seed (I know, not great, but
  // the audio toolbox took away my analogRead)
  int seed = micros() % 32767;
  if ( DEBUG ) {
    Serial.print("Seed: ");
    Serial.println(seed);
  }
  randomSeed(seed);

  if ( DEBUG ) {
    Serial.println("Finished init");
  }
}

void loop() {

  if ( (fps > 24) && peak1.available() ) {

    // State machine
    switch ( state ) {

      // Wait until the mic picks up some sound
      case QUIET:
        if ( peak1.read() > SQUELCH_CUTOFF ) {
          timer = millis();
          state = QUIET_TO_LOUD;
        }
        break;

      // If sound continues, play sound effect
      case QUIET_TO_LOUD:
        if ( peak1.read() <= SQUELCH_CUTOFF ) {
          state = QUIET;
        } else {
          if ( millis() > timer + HYSTERESIS_TIME_ON ) {

            if ( DEBUG ) {
              Serial.println("ON");
            }

            // Turn on amp, play sound, turn on mic
            digitalWrite(AMP_ENABLE, HIGH);
            if ( BEGIN_CLICK ) {
              playFile("click.raw");
            }
            mixer1.gain(0, BASS_GAIN_ON);
            mixer1.gain(1, TREBLE_GAIN_ON);

            // Go to next state
            state = LOUD;
          }
        }
        break;

      // Filter mic input and play it through speakers
      case LOUD:
        if ( peak1.read() <= SQUELCH_CUTOFF ) {
          timer = millis();
          state = LOUD_TO_QUIET;
        }
        break;

      // If no sound for a time, play click or burst
      case LOUD_TO_QUIET:
        if ( peak1.read() > SQUELCH_CUTOFF ) {
          state = LOUD;
        } else {
          if ( millis() > timer + HYSTERESIS_TIME_OFF ) {

            if ( DEBUG ) {
              Serial.println("OFF");
            }

            // Play a random sound
            if ( END_SOUND ) {
              if ( random(2) ) {
                playFile("click.raw");
              } else {
                playFile("break.raw");
              }
            }

            // Turn off mic and amp
            digitalWrite(AMP_ENABLE, LOW);
            mixer1.gain(0, BASS_GAIN_OFF);
            mixer1.gain(1, TREBLE_GAIN_OFF);
            state = QUIET;
          }
        }
        break;

      // You really shouldn't get here
      default:
        break;
    }
  }
}

// Play a sound clip from serial flash
void playFile( const char* filename ) {

  if ( DEBUG ) {
    Serial.print("Playing file: ");
    Serial.print(filename);
  }

  // Start playing the file
  playFlashRaw1.play(filename);

  // A brief delay for the library read info
  delay(5);

  // Wait for the file to finish playing
  while ( playFlashRaw1.isPlaying() );

  if ( DEBUG ) {
    Serial.println("...done");
  }
}

Make sure the board has the following settings:

  • Board: Teensy 3.2 / 3.1
  • USB Type: Serial
  • CPU Speed: 96 MHz optimized (overclock)
  • Port: \

Upload the Vox Imperium to the Teensy

Upload the sketch to the Teensy, and you're ready to join the Imperial Army!

Run It!

Whenever you speak into the microphone, you'll hear a click followed by a nasal version of your voice. When you stop talking, the Teensy will play a click or a static burst. You can disable the initial click by changing BEGIN_CLICK to false, and you can disable the ending sound by changing END_SOUND to false.

You can also plug a LiPo battery into the Power Cell to power the whole contraption.

Powering the Vox Imperium off a battery