Change Flange effect to one channel

effect_flange.cpp

 /******************************************************************/
 //                A u d i o E f f e c t F l a n g e
 // Written by Pete (El Supremo) Jan 2014
+// 140529 - change to handle mono stream and change modify() to voices()
 // 140207 - fix calculation of delay_rate_incr which is expressed as
 //			a fraction of 2*PI
 // 140207 - cosmetic fix to begin()
 }
   delay_length = d_length/2;
   l_delayline = delayline;
-  r_delayline = delayline + delay_length;
   
   delay_depth = d_depth;
   // initial index
   l_delay_rate_index = 0;
-  r_delay_rate_index = 0;
   l_circ_idx = 0;
-  r_circ_idx = 0;
   delay_rate_incr = delay_rate/44100.*2147483648.; 
 //Serial.println(delay_rate_incr,HEX);
 
 }
 
 
-boolean AudioEffectFlange::modify(int delay_offset,int d_depth,float delay_rate)
+boolean AudioEffectFlange::voices(int delay_offset,int d_depth,float delay_rate)
 {
   boolean all_ok = true;
   
     all_ok = false;
   }
   l_delay_rate_index = 0;
-  r_delay_rate_index = 0;
   l_circ_idx = 0;
-  r_circ_idx = 0;
   return(all_ok);
 }
 
   int idx1;
 
   if(l_delayline == NULL)return;
-  if(r_delayline == NULL)return; 
 
   // do passthru
   if(delay_offset_idx == FLANGE_DELAY_PASSTHRU) {
     block = receiveWritable(0);
     if(block) {
       bp = block->data;
+      // fill the delay line
       for(int i = 0;i < AUDIO_BLOCK_SAMPLES;i++) {
         l_circ_idx++;
         if(l_circ_idx >= delay_length) {
         }
         l_delayline[l_circ_idx] = *bp++;
       }
+      // transmit the unmodified block
       transmit(block,0);
       release(block);
     }
-    block = receiveWritable(1);
-    if(block) {
-      bp = block->data;
-      for(int i = 0;i < AUDIO_BLOCK_SAMPLES;i++) {
-        r_circ_idx++;
-        if(r_circ_idx >= delay_length) {
-          r_circ_idx = 0;
-        }
-        r_delayline[r_circ_idx] = *bp++;
-      }
-      transmit(block,1);
-      release(block);
-    }
     return;
   }
 
       // Do the interpolation
       frac = (l_delay_rate_index >> 1) &0x7fff;
       frac = (( (int)(l_delayline[idx1] - l_delayline[idx])*frac) >> 15);
-
-//frac = 0;
-      *bp++ = (l_delayline[l_circ_idx]
-                + l_delayline[idx] + frac
-//                + l_delayline[(l_circ_idx + delay_length/2) % delay_length]
-              )/2;
+      *bp++ = (l_delayline[l_circ_idx]+ l_delayline[idx] + frac)/2;
 
       l_delay_rate_index += delay_rate_incr;
       if(l_delay_rate_index & 0x80000000) {
     transmit(block,0);
     release(block);
   }
-
-  //          R I G H T  C H A N N E L
-
-  block = receiveWritable(1);
-  if(block) {
-    bp = block->data;
-    for(int i = 0;i < AUDIO_BLOCK_SAMPLES;i++) {
-      r_circ_idx++;
-      if(r_circ_idx >= delay_length) {
-        r_circ_idx = 0;
-      }
-      r_delayline[r_circ_idx] = *bp;
-      frac = arm_sin_q15( (q15_t)((r_delay_rate_index >> 16)&0x7fff));
-      idx = (frac * delay_depth) >> 15;
-
-      idx = r_circ_idx - (delay_offset_idx + idx);
-      if(idx < 0) {
-        idx += delay_length;
-      }
-      if(idx >= delay_length) {
-        idx -= delay_length;
-      }
-
-      if(frac < 0)
-        idx1 = idx - 1;
-      else
-        idx1 = idx + 1;
-      if(idx1 < 0) {
-        idx1 += delay_length;
-      }
-      if(idx1 >= delay_length) {
-        idx1 -= delay_length;
-      }
-      frac = (r_delay_rate_index >> 1) &0x7fff;
-      frac = (( (int)(r_delayline[idx1] - r_delayline[idx])*frac) >> 15);
-
-//frac = 0;
-      *bp++ = (r_delayline[r_circ_idx]
-                + r_delayline[idx] + frac
-               )/2;
-
-      r_delay_rate_index += delay_rate_incr;
-      if(r_delay_rate_index & 0x80000000) {
-        r_delay_rate_index &= 0x7fffffff;
-      }
-
-    }
-    // send the effect output to the right channel
-    transmit(block,1);
-    release(block);
-  }
 }
 
 

effect_flange.h

 /******************************************************************/
 //                A u d i o E f f e c t F l a n g e
 // Written by Pete (El Supremo) Jan 2014
+// 140529 - change to handle mono stream and change modify() to voices()
 
 #define FLANGE_DELAY_PASSTHRU 0
 
 {
 public:
   AudioEffectFlange(void): 
-  AudioStream(2,inputQueueArray) { 
+  AudioStream(1,inputQueueArray) { 
   }
 
   boolean begin(short *delayline,int d_length,int delay_offset,int d_depth,float delay_rate);
-  boolean modify(int delay_offset,int d_depth,float delay_rate);
+  boolean voices(int delay_offset,int d_depth,float delay_rate);
   virtual void update(void);
   void stop(void);
   
 private:
-  audio_block_t *inputQueueArray[2];
+  audio_block_t *inputQueueArray[1];
   short *l_delayline;
-  short *r_delayline;
   int delay_length;
   short l_circ_idx;
-  short r_circ_idx;
   int delay_depth;
   int delay_offset_idx;
   int   delay_rate_incr;
   unsigned int l_delay_rate_index;
-  unsigned int r_delay_rate_index;
 };
 
 #endif

examples/Effects/Flange/Flange.ino

 /*
-Change the chorus code to produce a flange effect
-140219
-  e
+VERSION 2 - use modified library which has been changed to handle
+            one channel instead of two
+            
+Proc = 21 (22),  Mem = 4 (6)
+140529
+  2a
+  - default at startup is to have passthru ON and the button
+    switches the flange effect in.
+  
+
+From: http://www.cs.cf.ac.uk/Dave/CM0268/PDF/10_CM0268_Audio_FX.pdf
+about Comb filter effects
+Effect      Delay range (ms)    Modulation
+Resonator      0 - 20            None
+Flanger        0 - 15            Sinusoidal (approx 1Hz)
+Chorus        25 - 50            None
+Echo            >50              None
 
 FMI:
 The audio board uses the following pins.
 #include <SPI.h>
 #include <Bounce.h>
 
-// Number of samples in ONE channel
+// Number of samples in each delay line
 #define FLANGE_DELAY_LENGTH (6*AUDIO_BLOCK_SAMPLES)
-// Allocate the delay line for left and right channels
-// The delayline will hold left and right samples so it
-// should be declared to be twice as long as the desired
-// number of samples in one channel
-#define FLANGE_DELAYLINE (FLANGE_DELAY_LENGTH*2)
-// The delay line for left and right channels
-short delayline[FLANGE_DELAYLINE];
-
-// If this pin is grounded the effect is turned off,
-// which makes it just pass through the audio
+// Allocate the delay lines for left and right channels
+short l_delayline[FLANGE_DELAY_LENGTH];
+short r_delayline[FLANGE_DELAY_LENGTH];
+
+// Default is to just pass the audio through. Grounding this pin
+// applies the flange effect
 // Don't use any of the pins listed above
 #define PASSTHRU_PIN 1
 
 const int myInput = AUDIO_INPUT_LINEIN;
 
 AudioInputI2S       audioInput;         // audio shield: mic or line-in
-AudioEffectFlange   myEffect;
+AudioEffectFlange   l_myEffect;
+AudioEffectFlange   r_myEffect;
 AudioOutputI2S      audioOutput;        // audio shield: headphones & line-out
 
 // Create Audio connections between the components
 // Both channels of the audio input go to the flange effect
-AudioConnection c1(audioInput, 0, myEffect, 0);
-AudioConnection c2(audioInput, 1, myEffect, 1);
+AudioConnection c1(audioInput, 0, l_myEffect, 0);
+AudioConnection c2(audioInput, 1, r_myEffect, 0);
 // both channels from the flange effect go to the audio output
-AudioConnection c3(myEffect, 0, audioOutput, 0);
-AudioConnection c4(myEffect, 1, audioOutput, 1);
+AudioConnection c3(l_myEffect, 0, audioOutput, 0);
+AudioConnection c4(r_myEffect, 0, audioOutput, 1);
 
 AudioControlSGTL5000 audioShield;
 
-/* 
-int s_idx = FLANGE_DELAY_LENGTH/2;
-int s_depth = FLANGE_DELAY_LENGTH/16;
-double s_freq = 1;
-
-// <<<<<<<<<<<<<<>>>>>>>>>>>>>>>>
-// 12
-int s_idx = FLANGE_DELAY_LENGTH/2;
-int s_depth = FLANGE_DELAY_LENGTH/8;
-double s_freq = .125;
-// with .125 the ticking is about 1Hz with music
-// but with the noise sample it is a bit slower than that
-// <<<<<<<<<<<<<<>>>>>>>>>>>>>>>>
-*/
-/*
-// <<<<<<<<<<<<<<>>>>>>>>>>>>>>>>
-// 12
-int s_idx = FLANGE_DELAY_LENGTH/2;
-int s_depth = FLANGE_DELAY_LENGTH/12;
-double s_freq = .125;
-// with .125 the ticking is about 1Hz with music
-// but with the noise sample it is a bit slower than that
-// <<<<<<<<<<<<<<>>>>>>>>>>>>>>>>
-*/
-/*
-//12
-int s_idx = 15*FLANGE_DELAY_LENGTH/16;
-int s_depth = 15*FLANGE_DELAY_LENGTH/16;
-double s_freq = 0;
-*/
-/*
-//12
-int s_idx = 2*FLANGE_DELAY_LENGTH/4;
-int s_depth = FLANGE_DELAY_LENGTH/8;
-double s_freq = .0625;
-*/
-
-/*
-//12 - good with Eric Clapton Unplugged
-int s_idx = 3*FLANGE_DELAY_LENGTH/4;
-int s_depth = FLANGE_DELAY_LENGTH/8;
-double s_freq = .0625;
-*/
-
-/*
-// Real flange effect! delay line is 2*
-int s_idx = 2*FLANGE_DELAY_LENGTH/4;
-int s_depth = FLANGE_DELAY_LENGTH/4;
-double s_freq = 2;
-*/
 
-/* 2 - 
-int s_idx = 2*FLANGE_DELAY_LENGTH/4;
-int s_depth = FLANGE_DELAY_LENGTH/8;
-double s_freq = 4;
-*/
-/*
-// 4
-int s_idx = FLANGE_DELAY_LENGTH/4;
-int s_depth = FLANGE_DELAY_LENGTH/4;
-double s_freq = .25;
-*/
-// 4
 int s_idx = FLANGE_DELAY_LENGTH/4;
 int s_depth = FLANGE_DELAY_LENGTH/4;
 double s_freq = .5;
     Serial.println(") is grounded");
   }
 
-  // Set up the flange effect
-  // - address of delayline
-  // - total number of samples (left AND right) in the delay line
-  // - Index (in samples) into the delay line for the added voice
-  // - Depth of the flange effect
-  // - frequency of the flange effect
-  myEffect.begin(delayline,FLANGE_DELAYLINE,s_idx,s_depth,s_freq);
+  // Set up the flange effect:
+  // address of delayline
+  // total number of samples in the delay line
+  // Index (in samples) into the delay line for the added voice
+  // Depth of the flange effect
+  // frequency of the flange effect
+  l_myEffect.begin(l_delayline,FLANGE_DELAY_LENGTH,s_idx,s_depth,s_freq);
+  r_myEffect.begin(r_delayline,FLANGE_DELAY_LENGTH,s_idx,s_depth,s_freq);
+  // Initially the effect is off. It is switched on when the
+  // PASSTHRU button is pushed.
+  l_myEffect.voices(FLANGE_DELAY_PASSTHRU,0,0);
+  r_myEffect.voices(FLANGE_DELAY_PASSTHRU,0,0);
 
   // I want output on the line out too
   audioShield.unmuteLineout();
   
   Serial.println("setup done");
-AudioProcessorUsageMaxReset();
-AudioMemoryUsageMaxReset();
+  AudioProcessorUsageMaxReset();
+  AudioMemoryUsageMaxReset();
 }
 
 
   // update the button
   b_passthru.update();
  
-  // If the passthru button is pushed, save the current
+  // If the passthru button is pushed
+  // turn the flange effect on
   // filter index and then switch the effect to passthru
   if(b_passthru.fallingEdge()) {
-    myEffect.modify(DELAY_PASSTHRU,0,0);
+    l_myEffect.voices(s_idx,s_depth,s_freq);
+    r_myEffect.voices(s_idx,s_depth,s_freq);
   }
   
-  // If passthru button is released, restore the effect
+  // If passthru button is released restore passthru
   if(b_passthru.risingEdge()) {
-    myEffect.modify(s_idx,s_depth,s_freq);
+    l_myEffect.voices(FLANGE_DELAY_PASSTHRU,0,0);
+    r_myEffect.voices(FLANGE_DELAY_PASSTHRU,0,0);
   }
 
 }

examples/Effects/Flange/effects_info.h

   combines the most recent sample, the oldest sample and the sample
   in the middle of the delay line.
   For two voices the effect can be represented as:
-  result = sample(0) + sample(dt)
+  result = (sample(0) + sample(dt))/2
   where sample(0) represents the current sample and sample(dt) is
   the sample in the delay line from dt milliseconds ago.
 
-
 FLANGE EFFECT
   This combines only one sample from the delay line but the position
   of that sample varies sinusoidally.
   -depth to +depth. Thus, the delayed sample will be selected from
   the range (dt-depth) to (dt+depth). This selection will vary
   at whatever rate is specified as the frequency of the effect Fe.
-  I have found that rates of .25 seconds or less are best, otherwise
-  the effect is very "watery" and in extreme cases the sound is
-  even off-key!
+
+Try these settings:
+#define FLANGE_DELAY_LENGTH (2*AUDIO_BLOCK_SAMPLES)
+and
+int s_idx = 2*FLANGE_DELAY_LENGTH/4;
+int s_depth = FLANGE_DELAY_LENGTH/4;
+double s_freq = 3;
+The flange effect can also produce a chorus effect if a longer
+delay line is used with a slower rate, for example try:
+#define FLANGE_DELAY_LENGTH (12*AUDIO_BLOCK_SAMPLES)
+and
+int s_idx = 3*FLANGE_DELAY_LENGTH/4;
+int s_depth = FLANGE_DELAY_LENGTH/8;
+double s_freq = .0625;
 
   When trying out these effects with recorded music as input, it is
   best to use those where there is a solo voice which is clearly
-  "in front" of the accompaninemnt. Tracks which already contain
+  "in front" of the accompaniment. Tracks which already contain
   flange or chorus effects don't work well.
   
 */