CombFilter.ino

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

#define TEST_TONE

// Use these with the audio adaptor board
#define SDCARD_CS_PIN    10
#define SDCARD_MOSI_PIN  7
#define SDCARD_SCK_PIN   14

const int                DRY_SIGNAL_CHANNEL( 0 );
const int                FEED_FORWARD_CHANNEL( 1 );
const int                FEED_BACKWARD_CHANNEL( 2 );

const int                RESONANT_FREQ_PIN( 20 );
const int                RESONANCE_TIME_PIN( 17 );

/*
const float              FREQUENCIES[] =   {  65.41,            // C2
                                              69.30,            // C#2
                                              73.42,            // D2
                                              77.78,            // D#2
                                              82.41,            // E2
                                              87.31,            // F2
                                              92.50,            // F#2
                                              98.00,            // G2
                                              103.83,           // G#2
                                              110.00,           // A2
                                              116.54,           // A#2
                                              123.47,           // B2
                                            };
*/
const float              FREQUENCIES[] =   {  261.63,            // C4
                                              277.18,            // C#4
                                              293.66,            // D4
                                              311.13,            // D#4
                                              329.63,            // E4
                                              349.23,            // F4
                                              369.99,            // F#4
                                              392.00,            // G4
                                              415.30,           // G#4
                                              440.00,           // A4
                                              466.16,           // A#4
                                              493.88,           // B4
                                            };

#ifdef TEST_TONE

AudioSynthWaveformSine   test_tone;
AudioOutputI2S           audio_output;
AudioControlSGTL5000     sgtl5000_1;

AudioMixer4              delay_mixer;
AudioEffectDelay         feed_forward_delay;
AudioEffectDelay         feed_back_delay;

AudioConnection          patch_cord_1( test_tone, 0, delay_mixer, DRY_SIGNAL_CHANNEL );
AudioConnection          patch_cord_2( delay_mixer, 0, audio_output, 0 );
AudioConnection          patch_cord_3( test_tone, 0, feed_forward_delay, 0 );
AudioConnection          patch_cord_4( feed_forward_delay, 0, delay_mixer, FEED_FORWARD_CHANNEL );
AudioConnection          patch_cord_5( delay_mixer, 0, feed_back_delay, 0 );
AudioConnection          patch_cord_6( feed_back_delay, 0, delay_mixer, FEED_BACKWARD_CHANNEL );

#else // !TEST_TONE

AudioInputI2S            audio_input;
AudioOutputI2S           audio_output;
AudioControlSGTL5000     sgtl5000_1;

AudioMixer4              delay_mixer;
AudioEffectDelay         feed_forward_delay;
AudioEffectDelay         feed_back_delay;

AudioConnection          patch_cord_1( audio_input, 0, delay_mixer, DRY_SIGNAL_CHANNEL );
AudioConnection          patch_cord_2( delay_mixer, 0, audio_output, 0 );
AudioConnection          patch_cord_3( audio_input, 0, feed_forward_delay, 0 );
AudioConnection          patch_cord_4( feed_forward_delay, 0, delay_mixer, FEED_FORWARD_CHANNEL );
AudioConnection          patch_cord_5( delay_mixer, 0, feed_back_delay, 0 );
AudioConnection          patch_cord_6( feed_back_delay, 0, delay_mixer, FEED_BACKWARD_CHANNEL );

#endif // !TEST_TONE

float calculate_delay_time_ms( float resonant_frequency )
{
  return 1000.0f / resonant_frequency;
}

float calculate_feedback_multiplier( float delay_time_ms, float resonance_time_ms )
{
  const float p = delay_time_ms / resonance_time_ms;
  return powf( 0.001, p );
}

void setup()
{
  AudioMemory( 128 );

  sgtl5000_1.enable();
  sgtl5000_1.volume(0.8f);

  sgtl5000_1.lineInLevel( 10 );  // 0.56volts p-p
  sgtl5000_1.lineOutLevel( 13 );  // 3.16volts p-p

  Serial.begin(9600);
  delay( 1000 );
  
 #ifdef TEST_TONE
  test_tone.amplitude( 0.25f );
#endif

  Serial.print("Setup started!\n");

  const float delay_time_ms       = calculate_delay_time_ms( FREQUENCIES[2] ); // tuned to D2
  const float feedback_mult       = calculate_feedback_multiplier( delay_time_ms, 1000.0f );

  feed_forward_delay.delay( 0, delay_time_ms );
  feed_back_delay.delay( 0, delay_time_ms );

  delay_mixer.gain( DRY_SIGNAL_CHANNEL, 0.5f );
  delay_mixer.gain( FEED_BACKWARD_CHANNEL, feedback_mult * 0.0f );
  delay_mixer.gain( FEED_FORWARD_CHANNEL, feedback_mult * 0.5f );

  Serial.print("Delay time ms:");
  Serial.print(delay_time_ms);
  Serial.print(" feedback mult:");
  Serial.print(feedback_mult);
  Serial.print("\nSetup finished!\n");
}

void loop()
{
#ifdef TEST_TONE

    static int current_tone_index = 0;

    test_tone.frequency( FREQUENCIES[current_tone_index] );

    Serial.print("Tone index:");
    Serial.print( current_tone_index );
    Serial.print(" Freq:");
    Serial.println( FREQUENCIES[current_tone_index] );
    
    delay( 2000 );
    current_tone_index = ( current_tone_index + 1 ) % 12;

#endif
}