Added new preset filters

examples/Delay/AnalogDelayDemo/AnalogDelayDemo.ino

@@ -94,6 +94,13 @@ void setup() {
   analogDelay.mix(0.5f);
   analogDelay.feedback(0.0f);
 
+  //////////////////////////////////
+  // AnalogDelay filter selection //
+  // Uncomment to tryout the 3 different built-in filters.
+  //analogDelay.setFilter(AudioEffectAnalogDelay::Filter::DM3); // The default filter. Naturally bright echo (highs stay, lows fade away)
+  //analogDelay.setFilter(AudioEffectAnalogDelay::Filter::WARM); // A warm filter with a smooth frequency rolloff above 2Khz
+  //analogDelay.setFilter(AudioEffectAnalogDelay::Filter::DARK); // A very dark filter, with a sharp rolloff above 1Khz
+
   // Setup 2-stages of LPF, cutoff 4500 Hz, Q-factor 0.7071 (a 'normal' Q-factor)
   cabFilter.setLowpass(0, 4500, .7071);
   cabFilter.setLowpass(1, 4500, .7071);

src/AudioEffectAnalogDelay.h

@@ -30,10 +30,6 @@
 
 namespace BAGuitar {
 
-/// The number of stages in the analog-response Biquad filter
-constexpr unsigned MAX_NUM_FILTER_STAGES = 4;
-constexpr unsigned NUM_COEFFS_PER_STAGE = 5;
-
 /**************************************************************************//**
  * AudioEffectAnalogDelay models BBD based analog delays. It provides controls
  * for delay, feedback (or regen), mix and output level. All parameters can be
@@ -54,6 +50,12 @@ public:
 		NUM_CONTROLS ///< this can be used as an alias for the number of MIDI controls
 	};
 
+	enum class Filter {
+		DM3 = 0,
+	    WARM,
+		DARK
+	};
+
 	// *** CONSTRUCTORS ***
 	AudioEffectAnalogDelay() = delete;
 
@@ -133,9 +135,17 @@ public:
 	/// @param value the CC value from 0 to 127
 	void processMidi(int channel, int midiCC, int value);
 
+	// ** FILTER COEFFICIENTS **
+
+	/// Set the filter coefficients to one of the presets. See AudioEffectAnalogDelay::Filter
+	/// for options.
+	/// @details See AudioEffectAnalogDelayFIlters.h for more details.
+	/// @param filter the preset filter. E.g. AudioEffectAnalogDelay::Filter::WARM
+	void setFilter(Filter filter);
+
 	/// Override the default coefficients with your own. The number of filters stages affects how
 	/// much CPU is consumed.
-	/// @details The effect uses the CMSIS-DSP library for biquads which requires coefficents
+	/// @details The effect uses the CMSIS-DSP library for biquads which requires coefficents.
 	/// be in q31 format, which means they are 32-bit signed integers representing -1.0 to slightly
 	/// less than +1.0. The coeffShift parameter effectively multiplies the coefficients by 2^shift. <br>
 	/// Example: If you really want +1.5, must instead use +0.75 * 2^1, thus 0.75 in q31 format is
@@ -171,11 +181,6 @@ private:
 
 	// Coefficients
 	void m_constructFilter(void);
-//	int m_numStages;
-//	int m_coeffShift;
-//	int m_coeffs[MAX_NUM_FILTER_STAGES*NUM_COEFFS_PER_STAGE] = {};
-
-	//size_t m_callCount = 0;
 };
 
 }

src/effects/AudioEffectAnalogDelay.cpp

@@ -5,6 +5,7 @@
  *      Author: slascos
  */
 #include <new>
+#include "AudioEffectAnalogDelayFilters.h"
 #include "AudioEffectAnalogDelay.h"
 
 namespace BAGuitar {
@@ -12,16 +13,6 @@ namespace BAGuitar {
 constexpr int MIDI_CHANNEL = 0;
 constexpr int MIDI_CONTROL = 1;
 
-// BOSS DM-3 Filters
-constexpr unsigned DM3_COEFF_SHIFT = 2;
-constexpr int32_t DM3[5*MAX_NUM_FILTER_STAGES] = {
-    536870912,            988616936,            455608573,            834606945,           -482959709,
-    536870912,           1031466345,            498793368,            965834205,           -467402235,
-    536870912,           1105821939,            573646688,            928470657,           -448083489,
-    2339,                      5093,                 2776,            302068995,              4412722
-};
-
-
 AudioEffectAnalogDelay::AudioEffectAnalogDelay(float maxDelayMs)
 : AudioStream(1, m_inputQueueArray)
 {
@@ -58,7 +49,7 @@ AudioEffectAnalogDelay::~AudioEffectAnalogDelay()
 void AudioEffectAnalogDelay::m_constructFilter(void)
 {
 	// Use DM3 coefficients by default
-	m_iir = new IirBiQuadFilterHQ(MAX_NUM_FILTER_STAGES, reinterpret_cast<const int32_t *>(&DM3), DM3_COEFF_SHIFT);
+	m_iir = new IirBiQuadFilterHQ(DM3_NUM_STAGES, reinterpret_cast<const int32_t *>(&DM3), DM3_COEFF_SHIFT);
 }
 
 void AudioEffectAnalogDelay::setFilterCoeffs(int numStages, const int32_t *coeffs, int coeffShift)
@@ -66,6 +57,22 @@ void AudioEffectAnalogDelay::setFilterCoeffs(int numStages, const int32_t *coeff
 	m_iir->changeFilterCoeffs(numStages, coeffs, coeffShift);
 }
 
+void AudioEffectAnalogDelay::setFilter(Filter filter)
+{
+	switch(filter) {
+	case Filter::WARM :
+		m_iir->changeFilterCoeffs(WARM_NUM_STAGES, reinterpret_cast<const int32_t *>(&WARM), WARM_COEFF_SHIFT);
+		break;
+	case Filter::DARK :
+		m_iir->changeFilterCoeffs(DARK_NUM_STAGES, reinterpret_cast<const int32_t *>(&DARK), DARK_COEFF_SHIFT);
+		break;
+	case Filter::DM3 :
+	default:
+		m_iir->changeFilterCoeffs(DM3_NUM_STAGES, reinterpret_cast<const int32_t *>(&DM3), DM3_COEFF_SHIFT);
+		break;
+	}
+}
+
 void AudioEffectAnalogDelay::update(void)
 {
 	audio_block_t *inputAudioBlock = receiveReadOnly(); // get the next block of input samples

src/effects/AudioEffectAnalogDelayFilters.h

@@ -0,0 +1,83 @@
+/**************************************************************************//**
+ *  @file
+ *  @author Steve Lascos
+ *  @company Blackaddr Audio
+ *
+ *  This file constains precomputed co-efficients for the AudioEffectAnalogDelay
+ *  class.
+ *
+ *  @copyright This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.*
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *****************************************************************************/
+#include <cstdint>
+
+namespace BAGuitar {
+
+// The number of stages in the analog-response Biquad filter
+constexpr unsigned MAX_NUM_FILTER_STAGES = 4;
+constexpr unsigned NUM_COEFFS_PER_STAGE = 5;
+
+// Matlab/Octave can be helpful to design a filter. Once you have the IIR filter (bz,az) coefficients
+// in the z-domain, they can be converted to second-order-sections. AudioEffectAnalogDelay is designed
+// to accept up to a maximum of an 8th order filter, broken into four, 2nd order stages.
+//
+// Second order sections can be created with:
+// [sos] = tf2sos(bz,az);
+// The results coefficents must be converted the Q31 format required by the ARM CMSIS-DSP library. This means
+// all coefficients must lie between -1.0 and +0.9999. If your (bz,az) coefficients exceed this, you must divide
+// them down by a power of 2. For example, if your largest magnitude coefficient is -3.5, you must divide by
+// 2^shift where 4=2^2 and thus shift = 2. You must then mutliply by 2^31 to get a 32-bit signed integer value
+// that represents the required Q31 coefficient.
+
+// BOSS DM-3 Filters
+// b(z) = 1.0e-03 * (0.0032    0.0257    0.0900    0.1800    0.2250    0.1800    0.0900    0.0257    0.0032)
+// a(z) = 1.0000   -5.7677   14.6935  -21.3811   19.1491  -10.5202    3.2584   -0.4244   -0.0067
+constexpr unsigned DM3_NUM_STAGES = 4;
+constexpr unsigned DM3_COEFF_SHIFT = 2;
+constexpr int32_t DM3[5*MAX_NUM_FILTER_STAGES] = {
+    536870912,            988616936,            455608573,            834606945,           -482959709,
+    536870912,           1031466345,            498793368,            965834205,           -467402235,
+    536870912,           1105821939,            573646688,            928470657,           -448083489,
+    2339,                      5093,                 2776,            302068995,              4412722
+};
+
+
+// Blackaddr WARM Filter
+// Butterworth, 8th order, cutoff = 2000 Hz
+// Matlab/Octave command: [bz, az] = butter(8, 2000/44100/2);
+// b(z) = 1.0e-05 * (0.0086    0.0689    0.2411    0.4821    0.6027    0.4821    0.2411    0.0689    0.0086_
+// a(z) = 1.0000   -6.5399   18.8246  -31.1340   32.3473  -21.6114    9.0643   -2.1815    0.2306
+constexpr unsigned WARM_NUM_STAGES = 4;
+constexpr unsigned WARM_COEFF_SHIFT = 2;
+constexpr int32_t WARM[5*MAX_NUM_FILTER_STAGES] = {
+    536870912,1060309346,523602393,976869875,-481046241,
+    536870912,1073413910,536711084,891250612,-391829326,
+    536870912,1087173998,550475248,835222426,-333446881,
+    46,92,46,807741349,-304811072
+};
+
+// Blackaddr DARK Filter
+// Chebychev Type II, 8th order, stopband = 60db, cutoff = 1000 Hz
+// Matlab command: [bz, az] = cheby2(8, 60, 1000/44100/2);
+// b(z) = 0.0009   -0.0066    0.0219   -0.0423    0.0522   -0.0423    0.0219   -0.0066    0.0009
+// a(z) = 1.0000   -7.4618   24.3762  -45.5356   53.1991  -39.8032   18.6245   -4.9829    0.5836
+constexpr unsigned DARK_NUM_STAGES = 4;
+constexpr unsigned DARK_COEFF_SHIFT = 1;
+constexpr int32_t DARK[5*MAX_NUM_FILTER_STAGES] = {
+	1073741824,-2124867808,1073741824,2107780229,-1043948409,
+	1073741824,-2116080466,1073741824,2042553796,-979786242,
+	1073741824,-2077777790,1073741824,1964779896,-904264933,
+	957356,-1462833,957356,1896884898,-838694612
+};
+
+};