From 98db248b5b410dc7f0da979213ee175a0e29a92e Mon Sep 17 00:00:00 2001
From: Stefano D'Angelo <stefano.dangelo@orastron.com>
Date: Sat, 8 Apr 2023 08:25:05 +0200
Subject: [PATCH] improved bw_comb and bw_chorus, simplified fx_chorus

---
 .../fx_chorus/daisy-seed/config_daisy_seed.h  |  7 ++---
 examples/fx_chorus/src/bw_example_fx_chorus.c | 17 ++++-------
 examples/fx_chorus/src/bw_example_fx_chorus.h |  3 --
 examples/fx_chorus/src/config.h               |  9 ++----
 examples/fx_chorus/web/config.js              | 19 ++-----------
 include/bw_chorus.h                           | 28 ++++++++++++++-----
 include/bw_comb.h                             |  2 +-
 7 files changed, 35 insertions(+), 50 deletions(-)

diff --git a/examples/fx_chorus/daisy-seed/config_daisy_seed.h b/examples/fx_chorus/daisy-seed/config_daisy_seed.h
index 0e5825d..c56c264 100644
--- a/examples/fx_chorus/daisy-seed/config_daisy_seed.h
+++ b/examples/fx_chorus/daisy-seed/config_daisy_seed.h
@@ -26,14 +26,11 @@ struct config_pin {
 	int	pin;
 };
 
-#define NUM_PINS 	5
+#define NUM_PINS 	2
 
 static struct config_pin config_pins[NUM_PINS] = {
 	{ 0, 15 },
-	{ 1, 16 },
-	{ 2, 17 },
-	{ 3, 18 },
-	{ 4, 19 },
+	{ 1, 16 }
 };
 
 #endif
diff --git a/examples/fx_chorus/src/bw_example_fx_chorus.c b/examples/fx_chorus/src/bw_example_fx_chorus.c
index 6080c0e..9ddb7ce 100644
--- a/examples/fx_chorus/src/bw_example_fx_chorus.c
+++ b/examples/fx_chorus/src/bw_example_fx_chorus.c
@@ -22,6 +22,10 @@
 
 void bw_example_fx_chorus_init(bw_example_fx_chorus *instance) {
 	bw_chorus_init(&instance->chorus_coeffs, 0.1f);
+	bw_chorus_set_delay(&instance->chorus_coeffs, 0.005f);
+	bw_chorus_set_coeff_x(&instance->chorus_coeffs, 0.7071f);
+	bw_chorus_set_coeff_mod(&instance->chorus_coeffs, 1.f);
+	bw_chorus_set_coeff_fb(&instance->chorus_coeffs, -0.7071f);
 }
 
 void bw_example_fx_chorus_set_sample_rate(bw_example_fx_chorus *instance, float sample_rate) {
@@ -49,19 +53,10 @@ void bw_example_fx_chorus_set_parameter(bw_example_fx_chorus *instance, int inde
 	instance->params[index] = value;
 	switch (index) {
 	case p_rate:
-		bw_chorus_set_rate(&instance->chorus_coeffs, value);
-		break;
-	case p_delay:
-		bw_chorus_set_delay(&instance->chorus_coeffs, 0.1f * value);
+		bw_chorus_set_rate(&instance->chorus_coeffs, 0.01f + 1.99f * value * value * value);
 		break;
 	case p_amount:
-		bw_chorus_set_amount(&instance->chorus_coeffs, 0.05f * value);
-		break;
-	case p_input:
-		bw_chorus_set_coeff_x(&instance->chorus_coeffs, value);
-		break;
-	case p_mod:
-		bw_chorus_set_coeff_mod(&instance->chorus_coeffs, value);
+		bw_chorus_set_amount(&instance->chorus_coeffs, 0.004f * value);
 		break;
 	}
 }
diff --git a/examples/fx_chorus/src/bw_example_fx_chorus.h b/examples/fx_chorus/src/bw_example_fx_chorus.h
index 19aaf9f..80bc66b 100644
--- a/examples/fx_chorus/src/bw_example_fx_chorus.h
+++ b/examples/fx_chorus/src/bw_example_fx_chorus.h
@@ -29,10 +29,7 @@ extern "C" {
 
 enum {
 	p_rate,
-	p_delay,
 	p_amount,
-	p_input,
-	p_mod,
 	p_n
 };
 
diff --git a/examples/fx_chorus/src/config.h b/examples/fx_chorus/src/config.h
index 434537d..15cf7b3 100644
--- a/examples/fx_chorus/src/config.h
+++ b/examples/fx_chorus/src/config.h
@@ -66,14 +66,11 @@ static struct config_io_bus config_buses_out[NUM_BUSES_OUT] = {
 	{ "Audio out", 1, 0, 0, IO_MONO }
 };
 
-#define NUM_PARAMETERS		5
+#define NUM_PARAMETERS		2
 
 static struct config_parameter config_parameters[NUM_PARAMETERS] = {
-	{ "Modulation rate", "Rate", "", 0, 0, 0, 0.5f },
-	{ "Delay", "Delay", "s", 0, 0, 0, 0.5f },
-	{ "Modulation amount", "Mod amount", "", 0, 0, 0, 0.5f },
-	{ "Input", "Input", "", 0, 0, 0, 0.5f },
-	{ "Modulated branch", "Mod branch", "", 0, 0, 0, 0.5f },
+	{ "Rate", "Rate", "", 0, 0, 0, 0.5f },
+	{ "Depth", "Depth", "", 0, 0, 0, 0.5f },
 };
 
 // Internal API
diff --git a/examples/fx_chorus/web/config.js b/examples/fx_chorus/web/config.js
index 861dc56..f704641 100644
--- a/examples/fx_chorus/web/config.js
+++ b/examples/fx_chorus/web/config.js
@@ -31,27 +31,12 @@ var buses = [
 
 var parameters = [
 	{
-		name:		"Modulation rate",
+		name:		"Rate",
 		output:		false,
 		defaultValue:	0.5
 	},
 	{
-		name:		"Delay",
-		output:		false,
-		defaultValue:	0.5
-	},
-	{
-		name:		"Modulation amount",
-		output:		false,
-		defaultValue:	0.5
-	},
-	{
-		name:		"Input",
-		output:		false,
-		defaultValue:	0.5
-	},
-	{
-		name:		"Modulated branch",
+		name:		"Amount",
 		output:		false,
 		defaultValue:	0.5
 	}
diff --git a/include/bw_chorus.h b/include/bw_chorus.h
index fbf6bdc..af5ebf6 100644
--- a/include/bw_chorus.h
+++ b/include/bw_chorus.h
@@ -26,10 +26,13 @@
  *    bw_osc_sin bw_phase_gen
  *  }}}
  *  description {{{
- *    Chorus / vibrato with variable speed and amount.
+ *    Chorus / vibrato / flanger with variable rate and amount.
  *
  *    It outputs a mix of the dry input signal with itself going through a
- *    modulated delay.
+ *    modulated delay and an optional feedback, as explained in
+ *
+ *    J. Dattorro, "Effect Design, Part 2: Delay-Line Modulation and Chorus",
+ *    J. Audio Eng. Soc., vol. 45, no. 10, pp. 764-788, October 1997.
  *  }}}
  *  changelog {{{
  *    <ul>
@@ -156,9 +159,9 @@ static inline void bw_chorus_set_amount(bw_chorus_coeffs *BW_RESTRICT coeffs, fl
  *  ```>>> */
 static inline void bw_chorus_set_coeff_x(bw_chorus_coeffs *BW_RESTRICT coeffs, float value);
 /*! <<<```
- *    Sets the dry input coefficient `value` in `coeffs`.
+ *    Sets the input coefficient `value` in `coeffs`.
  *
- *    Default value: `0.f`.
+ *    Default value: `1.f`.
  *
  *    #### bw_chorus_set_coeff_mod()
  *  ```>>> */
@@ -166,7 +169,15 @@ static inline void bw_chorus_set_coeff_mod(bw_chorus_coeffs *BW_RESTRICT coeffs,
 /*! <<<```
  *    Sets the modulated branch coefficient `value` in `coeffs`.
  *
- *    Default value: `1.f`.
+ *    Default value: `0.f`.
+ *
+ *    #### bw_chorus_set_coeff_fb()
+ *  ```>>> */
+static inline void bw_chorus_set_coeff_fb(bw_chorus_coeffs *BW_RESTRICT coeffs, float value);
+/*! <<<```
+ *    Sets the feedback branch coefficient `value` in `coeffs`.
+ *
+ *    Default value: `0.f`.
  *  }}} */
 
 /*** Implementation ***/
@@ -197,8 +208,6 @@ struct _bw_chorus_state {
 static inline void bw_chorus_init(bw_chorus_coeffs *BW_RESTRICT coeffs, float max_delay) {
 	bw_phase_gen_init(&coeffs->phase_gen_coeffs);
 	bw_comb_init(&coeffs->comb_coeffs, max_delay);
-	bw_comb_set_coeff_blend(&coeffs->comb_coeffs, 0.f);
-	bw_comb_set_coeff_ff(&coeffs->comb_coeffs, 1.f);
 	coeffs->delay = 0.f;
 	coeffs->amount = 0.f;
 }
@@ -258,6 +267,7 @@ static inline void bw_chorus_set_rate(bw_chorus_coeffs *BW_RESTRICT coeffs, floa
 }
 
 static inline void bw_chorus_set_delay(bw_chorus_coeffs *BW_RESTRICT coeffs, float value) {
+	bw_comb_set_delay_fb(&coeffs->comb_coeffs, value);
 	coeffs->delay = value;
 }
 
@@ -273,6 +283,10 @@ static inline void bw_chorus_set_coeff_mod(bw_chorus_coeffs *BW_RESTRICT coeffs,
 	bw_comb_set_coeff_ff(&coeffs->comb_coeffs, value);
 }
 
+static inline void bw_chorus_set_coeff_fb(bw_chorus_coeffs *BW_RESTRICT coeffs, float value) {
+	bw_comb_set_coeff_fb(&coeffs->comb_coeffs, value);
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/include/bw_comb.h b/include/bw_comb.h
index 61e43f5..6851c16 100644
--- a/include/bw_comb.h
+++ b/include/bw_comb.h
@@ -218,7 +218,7 @@ static inline void bw_comb_init(bw_comb_coeffs *BW_RESTRICT coeffs, float max_de
 	bw_gain_init(&coeffs->fb_coeffs);
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.05f);
-	bw_one_pole_set_sticky_thresh(&coeffs->smooth_coeffs, 1e-3f);
+	bw_one_pole_set_sticky_thresh(&coeffs->smooth_coeffs, 1e-6f);
 	bw_gain_set_gain_lin(&coeffs->ff_coeffs, 0.f);
 	bw_gain_set_gain_lin(&coeffs->fb_coeffs, 0.f);
 	coeffs->delay_ff = 0.f;