Fixes.

MicroMDAEPiano.ino

@@ -57,16 +57,14 @@ AudioAmplifier           inverter;
 AudioEffectModulatedDelay   modchorus_r;
 AudioEffectModulatedDelay   modchorus_l;
 AudioSynthWaveform       modulator;
-AudioFilterBiquad        modulator_filter;
 AudioConnection          patchCord0(queue_r, peak_r);
 AudioConnection          patchCord1(queue_l, peak_l);
 AudioConnection          patchCord2(queue_r, freeverb_r);
 AudioConnection          patchCord3(queue_l, freeverb_l);
 AudioConnection          patchCord4(queue_r, 0, modchorus_r, 0);
 AudioConnection          patchCord5(queue_l, 0, modchorus_l, 0);
-AudioConnection          patchCord6(modulator, modulator_filter);
-AudioConnection          patchCord7(modulator_filter, 0, modchorus_r, 1);
-AudioConnection          patchCord8(modulator_filter, inverter);
+AudioConnection          patchCord6(modulator, 0, modchorus_r, 1);
+AudioConnection          patchCord8(modulator, inverter);
 AudioConnection          patchCord9(inverter, 0, modchorus_l, 1);
 AudioConnection          patchCord10(queue_r, 0, mixer_r, 0);
 AudioConnection          patchCord11(queue_l, 0, mixer_l, 0);
@@ -235,7 +233,6 @@ void setup()
   modulator.phase(0);
   modulator.amplitude(1.0);
   modulator.offset(0.0);
-  modulator_filter.setLowpass(0, CHORUS_MODULATOR_FILTER_FRQ, CHORUS_MODULATOR_FILTER_Q);
   inverter.gain(-1.0); // change phase for second modulated delay (faked stereo mode)
   modchorus_r.offset(15.0);
   modchorus_l.offset(15.0);

config.h

@@ -57,9 +57,10 @@
 // CHORUS parameters
 #define CHORUS_DELAY_LENGTH_SAMPLES (15*AUDIO_BLOCK_SAMPLES) // one AUDIO_BLOCK_SAMPLES = 2.902ms
 #define CHORUS_WAVEFORM WAVEFORM_TRIANGLE // WAVEFORM_SINE WAVEFORM_TRIANGLE WAVEFORM_SAWTOOTH WAVEFORM_SAWTOOTH_REVERSE
-#define CHORUS_MODULATOR_FILTER_FRQ 10 // see https://www.earlevel.com/main/2013/10/13/biquad-calculator-v2/
-#define CHORUS_MODULATOR_FILTER_Q 0.7
-
+//#define CHORUS_MODULATOR_FILTER_FRQ 10 // see https://www.earlevel.com/main/2013/10/13/biquad-calculator-v2/
+//#define CHORUS_MODULATOR_FILTER_Q 0.7
+#define CHORUS_MODULATOR_BIQUAD 1
+//#define CHORUS_OUTPUT_BIQUAD 1
 //*************************************************************************************************
 //* DEBUG OUTPUT SETTINGS
 //*************************************************************************************************

effect_modulated_delay.cpp

@@ -58,6 +58,22 @@ boolean AudioEffectModulatedDelay::begin(short *delayline, int d_length)
   _delayline = delayline;
   _delay_length = d_length;
 
+#ifdef CHORUS_MODULATOR_BIQUAD
+  mod_lp_coeffs[0] = -1.98982427; // https://arachnoid.com/BiQuadDesigner/ Lopass Fc=50Hz, Q=0.7
+  mod_lp_coeffs[1] = 0.98987476;
+  mod_lp_coeffs[2] = 1.26228228e-5;
+  mod_lp_coeffs[3] = 2.52456456e-5;
+  mod_lp_coeffs[4] = 1.26228228e-5;
+  biquad_mod = {1, mod_lp_state, mod_lp_coeffs};
+#endif
+#ifdef CHORUS_OUTUT_BIQUAD // https://web.fhnw.ch/technik/projekte/eit/Fruehling2016/MuelZum/html/parametric__equalizer__example_8c_source.html
+  out_lp_coeffs[0] = -0.10987036; // https://arachnoid.com/BiQuadDesigner/ Lopass Fc=10000Hz, Q=0.3
+  out_lp_coeffs[1] = -0.24497694;
+  out_lp_coeffs[2] = 0.16128817;
+  out_lp_coeffs[3] = 0.32257635;
+  out_lp_coeffs[4] = 0.16128817;
+  biquad_out = {1, out_lp_state, out_lp_coeffs, 0};
+#endif
   return (true);
 }
 
@@ -84,6 +100,9 @@ void AudioEffectModulatedDelay::update(void)
     bp = block->data;
     arm_q15_to_float(modulation->data, mod_float, AUDIO_BLOCK_SAMPLES);
     mp = mod_float;
+#ifdef CHORUS_MODULATOR_BIQUAD
+    arm_biquad_cascade_df1_f32(&biquad_mod, mod_float, mod_float, AUDIO_BLOCK_SAMPLES);
+#endif
 
     for (uint16_t i = 0; i < AUDIO_BLOCK_SAMPLES; i++)
     {
@@ -93,11 +112,11 @@ void AudioEffectModulatedDelay::update(void)
       _delayline[_circ_idx] = *bp;
 
       // Calculate the modulation-index as a floating point number for interpolation
-      mod_idx = _delay_offset + (*mp * (1 - MODULATION_MAX_FACTOR) * _delay_length);
+      mod_idx = *mp * (1 - MODULATION_MAX_FACTOR) * _delay_length;
       mod_fraction = modff(mod_idx, &mod_number);
 
       // calculate modulation index into circular buffer
-      c_mod_idx = (_circ_idx - int(mod_number)) % _delay_length;
+      c_mod_idx = (_circ_idx - _delay_offset - int(mod_number)) % _delay_length;
       if (c_mod_idx < 0) // check for negative offsets and correct them
         c_mod_idx += _delay_length;
 
@@ -117,7 +136,11 @@ void AudioEffectModulatedDelay::update(void)
         idx[0] = c_mod_idx + 1;
         idx[1] = c_mod_idx;
       }
-      *bp = round(float(_delayline[idx[0]]) * (mod_fraction) + float(_delayline[idx[1]]) * (1.0 - mod_fraction));
+      if (mod_idx < 0.0)
+        *bp = round(float(_delayline[idx[0]]) * (mod_fraction) + float(_delayline[idx[1]]) * (1.0 - mod_fraction));
+      else
+        *bp = round(float(_delayline[idx[0]]) * (1.0 - mod_fraction) + float(_delayline[idx[1]]) * mod_fraction);
+
 
       // push the pointers forward
       bp++; // next audio data
@@ -131,6 +154,9 @@ void AudioEffectModulatedDelay::update(void)
 
   if (block)
   {
+#ifdef CHORUS_OUTPUT_BIQUAD
+    arm_biquad_cascade_df1_fast_q15(&biquad_out, (q15_t*)block, (q15_t*)block, AUDIO_BLOCK_SAMPLES);
+#endif
     transmit(block, 0);
     release(block);
   }

effect_modulated_delay.h

@@ -56,6 +56,16 @@ class AudioEffectModulatedDelay :
     uint16_t _delay_length;
     int16_t c_mod_idx;
     uint16_t idx[2];
+#ifdef CHORUS_MODULATOR_BIQUAD
+    arm_biquad_casd_df1_inst_f32 biquad_mod;
+    float mod_lp_state[2];
+    float mod_lp_coeffs[5];
+#endif
+#ifdef CHORUS_OUTPUT_BIQUAD
+    arm_biquad_casd_df1_inst_q15 biquad_out;
+    float out_lp_state[2];
+    float out_lp_coeffs[5];
+#endif
 };
 
 #endif