Change Chrous effect to one channel

effect_chorus.cpp

@@ -26,6 +26,7 @@
 
 //                A u d i o E f f e c t C h o r u s
 // Written by Pete (El Supremo) Jan 2014
+// 140529 - change to handle mono stream - change modify() to voices()
 // 140219 - correct storage class (not static)
 
 boolean AudioEffectChorus::begin(short *delayline,int d_length,int n_chorus)
@@ -37,10 +38,8 @@ Serial.print(n_chorus);
 Serial.println(")");
 
   l_delayline = NULL;
-  r_delayline = NULL;
   delay_length = 0;
   l_circ_idx = 0;
-  r_circ_idx = 0;
 
   if(delayline == NULL) {
     return(false);
@@ -53,14 +52,13 @@ Serial.println(")");
   }
   
   l_delayline = delayline;
-  r_delayline = delayline + d_length/2;
   delay_length = d_length/2;
   num_chorus = n_chorus;
  
   return(true);
 }
 
-void AudioEffectChorus::modify(int n_chorus)
+void AudioEffectChorus::voices(int n_chorus)
 {
   num_chorus = n_chorus;
 }
@@ -74,7 +72,6 @@ void AudioEffectChorus::update(void)
   int c_idx;
 
   if(l_delayline == NULL)return;
-  if(r_delayline == NULL)return;  
   
   // do passthru
   // It stores the unmodified data in the delay line so that
@@ -94,20 +91,6 @@ void AudioEffectChorus::update(void)
       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;
   }
 
   //          L E F T  C H A N N E L
@@ -133,38 +116,10 @@ void AudioEffectChorus::update(void)
       *bp++ = sum/num_chorus;
     }
 
-    // send the effect output to the left channel
+    // transmit the block
     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;
-      sum = 0;
-      c_idx = r_circ_idx;
-      for(int k = 0; k < num_chorus; k++) {
-        sum += r_delayline[c_idx];
-        if(num_chorus > 1)c_idx -= delay_length/(num_chorus - 1) - 1;
-        if(c_idx < 0) {
-          c_idx += delay_length;
-        }
-      }
-      *bp++ = sum/num_chorus;
-    }
-
-    // send the effect output to the left channel
-    transmit(block,1);
-    release(block);
-  }
 }
 
 

effect_chorus.h

@@ -38,20 +38,18 @@ public AudioStream
 {
 public:
   AudioEffectChorus(void):
-  AudioStream(2,inputQueueArray), num_chorus(2)
+  AudioStream(1,inputQueueArray), num_chorus(2)
   { }
 
   boolean begin(short *delayline,int delay_length,int n_chorus);
   virtual void update(void);
   void stop(void);
-  void modify(int n_chorus);
+  void voices(int n_chorus);
   
 private:
-  audio_block_t *inputQueueArray[2];
+  audio_block_t *inputQueueArray[1];
   short *l_delayline;
-  short *r_delayline;
   short l_circ_idx;
-  short r_circ_idx;
   int num_chorus;
   int delay_length;
 };

examples/Effects/Chorus/Chorus.ino

@@ -1,8 +1,21 @@
 /*
-PROC/MEM 9/4
+VERSION 2 - use modified library which has been changed to handle
+            one channel instead of two
+140529
+Proc = 7 (7),  Mem = 4 (4)
+  2a
+  - default at startup is to have passthru ON and the button
+    switches the chorus effect in.
+  
+previous performance measures were PROC/MEM 9/4
 
-140219
-  p
+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.
@@ -41,18 +54,14 @@ many blocks you provided with AudioMemory().
 
 
 
-// Number of samples in ONE channel
+// Number of samples in each delay line
 #define CHORUS_DELAY_LENGTH (16*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 CHORUS_DELAYLINE (CHORUS_DELAY_LENGTH*2)
-// The delay line for left and right channels
-short delayline[CHORUS_DELAYLINE];
-
-// If this pin is grounded the chorus is turned off
-// which makes it just pass through the audio
+// Allocate the delay lines for left and right channels
+short l_delayline[CHORUS_DELAY_LENGTH];
+short r_delayline[CHORUS_DELAY_LENGTH];
+
+// Default is to just pass the audio through. Grounding this pin
+// applies the chorus effect
 // Don't use any of the pins listed above
 #define PASSTHRU_PIN 1
 
@@ -62,16 +71,17 @@ Bounce b_passthru = Bounce(PASSTHRU_PIN,15);
 const int myInput = AUDIO_INPUT_LINEIN;
 
 AudioInputI2S       audioInput;         // audio shield: mic or line-in
-AudioEffectChorus   myEffect;
+AudioEffectChorus   l_myEffect;
+AudioEffectChorus   r_myEffect;
 AudioOutputI2S      audioOutput;        // audio shield: headphones & line-out
 
 // Create Audio connections between the components
 // Both channels of the audio input go to the chorus effect
-AudioConnection c1(audioInput, 0, myEffect, 0);
-AudioConnection c2(audioInput, 1, myEffect, 1);
-// both channels from the chorus effect go to the audio output
-AudioConnection c3(myEffect, 0, audioOutput, 0);
-AudioConnection c4(myEffect, 1, audioOutput, 1);
+AudioConnection c1(audioInput, 0, l_myEffect, 0);
+AudioConnection c2(audioInput, 1, r_myEffect, 0);
+// both channels chorus effects go to the audio output
+AudioConnection c3(l_myEffect, 0, audioOutput, 0);
+AudioConnection c4(r_myEffect, 0, audioOutput, 1);
 
 AudioControlSGTL5000 audioShield;
 
@@ -103,22 +113,35 @@ void setup() {
     Serial.println(") is grounded");
   }
 
-  // Initialize the effect
-  // - address of delayline
-  // - total number of samples (left AND right) in the delay line
-  // - number of voices in the chorus INCLUDING the original voice
-  if(!myEffect.begin(delayline,CHORUS_DELAYLINE,n_chorus)) {
-    Serial.println("AudioEffectChorus - begin failed");
+  // Initialize the effect - left channel
+  // address of delayline
+  // total number of samples in the delay line
+  // number of voices in the chorus INCLUDING the original voice
+  if(!l_myEffect.begin(l_delayline,CHORUS_DELAY_LENGTH,n_chorus)) {
+    Serial.println("AudioEffectChorus - left channel begin failed");
     while(1);
   }
-  
+
+  // Initialize the effect - right channel
+  // address of delayline
+  // total number of samples in the delay line
+  // number of voices in the chorus INCLUDING the original voice
+  if(!r_myEffect.begin(r_delayline,CHORUS_DELAY_LENGTH,n_chorus)) {
+    Serial.println("AudioEffectChorus - left channel begin failed");
+    while(1);
+  }
+  // Initially the effect is off. It is switched on when the
+  // PASSTHRU button is pushed.
+  l_myEffect.voices(0);
+  r_myEffect.voices(0);
+
   // I want output on the line out too
   audioShield.unmuteLineout();
 //  audioShield.muteHeadphone();
   
   Serial.println("setup done");
-AudioProcessorUsageMaxReset();
-AudioMemoryUsageMaxReset();
+  AudioProcessorUsageMaxReset();
+  AudioMemoryUsageMaxReset();
 }
 
 
@@ -151,14 +174,16 @@ if(0) {
   // update the button
   b_passthru.update();
  
-  // If the passthru button is pushed, switch the effect to passthru
+  // If the passthru button is pushed, switch the chorus on
   if(b_passthru.fallingEdge()) {
-    myEffect.modify(0);
+    l_myEffect.voices(n_chorus);
+    r_myEffect.voices(n_chorus);
   }
   
-  // If passthru button is released, restore the previous chorus
+  // If passthru button is released, turn on passthru
   if(b_passthru.risingEdge()) {
-    myEffect.modify(n_chorus);
+    l_myEffect.voices(0);
+    r_myEffect.voices(0);
   }
 
 }

examples/Effects/Chorus/effects_info.h

@@ -5,7 +5,7 @@ CHORUS and FLANGE effects
   occurred in the past. An obvious effect this would allow would be
   an echo where the current sample is combined with a sample from,
   say, 250 milliseconds ago. The chorus and flange effects do this
-  as well but they combine samples from only about 50ms or less ago.
+  as well but they combine samples from only about 50ms (or less) ago.
   
 CHORUS EFFECT
   This combines one or more samples up to about 50ms ago. In this
@@ -17,7 +17,7 @@ CHORUS EFFECT
   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.
 
@@ -31,13 +31,24 @@ FLANGE EFFECT
   -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.
   
 */