diff --git a/examples/Delay/AnalogDelayDemo/AnalogDelayDemo.ino b/examples/Delay/AnalogDelayDemo/AnalogDelayDemo.ino
index 1083140..bb6a910 100644
--- a/examples/Delay/AnalogDelayDemo/AnalogDelayDemo.ino
+++ b/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);
diff --git a/src/AudioEffectAnalogDelay.h b/src/AudioEffectAnalogDelay.h
index d84ad79..49b6e90 100644
--- a/src/AudioEffectAnalogDelay.h
+++ b/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.
/// 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;
};
}
diff --git a/src/effects/AudioEffectAnalogDelay.cpp b/src/effects/AudioEffectAnalogDelay.cpp
index f822a6e..6cf1ead 100644
--- a/src/effects/AudioEffectAnalogDelay.cpp
+++ b/src/effects/AudioEffectAnalogDelay.cpp
@@ -5,6 +5,7 @@
* Author: slascos
*/
#include
+#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(&DM3), DM3_COEFF_SHIFT);
+ m_iir = new IirBiQuadFilterHQ(DM3_NUM_STAGES, reinterpret_cast(&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(&WARM), WARM_COEFF_SHIFT);
+ break;
+ case Filter::DARK :
+ m_iir->changeFilterCoeffs(DARK_NUM_STAGES, reinterpret_cast(&DARK), DARK_COEFF_SHIFT);
+ break;
+ case Filter::DM3 :
+ default:
+ m_iir->changeFilterCoeffs(DM3_NUM_STAGES, reinterpret_cast(&DM3), DM3_COEFF_SHIFT);
+ break;
+ }
+}
+
void AudioEffectAnalogDelay::update(void)
{
audio_block_t *inputAudioBlock = receiveReadOnly(); // get the next block of input samples
diff --git a/src/effects/AudioEffectAnalogDelayFilters.h b/src/effects/AudioEffectAnalogDelayFilters.h
new file mode 100644
index 0000000..71f70bd
--- /dev/null
+++ b/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 .
+ *****************************************************************************/
+#include
+
+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
+};
+
+};