Add a Second Order All Pass Filter called Soap (#182)

* Update CMakeLists.txt and Makefile

Update CMakeLists.txt and Makefile to include soap filter

* update daisysp.h to include soap

update daisysp.h to include soap

* add soap filter 

add soap filter

* update to cmath, floats, add output options

change to <cmath> instead of math.h for trig functions. replaced doubles with floats for speed. added bandpass and bandreject output modes similar to svf filter

CMakeLists.txt

@@ -37,6 +37,7 @@ Source/Filters/moogladder.cpp
 Source/Filters/nlfilt.cpp
 Source/Filters/svf.cpp
 Source/Filters/tone.cpp
+Source/Filters/soap.cpp
 Source/Noise/clockednoise.cpp
 Source/Noise/grainlet.cpp
 Source/Noise/particle.cpp

Makefile

@@ -54,7 +54,8 @@ mode \
 moogladder \
 nlfilt \
 svf \
-tone 
+tone \
+soap 
 #fir
 
 NOISE_MOD_DIR = Noise

Source/Filters/soap.cpp

@@ -0,0 +1,61 @@
+#include "soap.h"
+#include <cmath>
+
+#define PI 3.141592653589793
+
+void Soap::Init(float sample_rate)
+{
+    soap_center_freq_ =        400.0;
+    soap_bandwidth_ =          50.0;
+    in_0_ =                    0.0;          // input            x0
+    din_1_ =                   0.0;          // delayed input    x1
+    din_2_ =                   0.0;          // delayed input    x2
+    dout_1_ =                  0.0;          // delayed output   y1
+    dout_2_ =                  0.0;          // delayed output   y2
+    all_output_ =              0.0;          // all pass output  y0
+    out_bandpass_ =            0.0;          // bandpass output
+    out_bandreject_ =          0.0;          // bandreject output
+    sr_ = sample_rate;
+    return;
+}
+
+void Soap::Process(float in)
+{
+    // recalculate the coefficients, later move this to a lookup table
+    float d = -std::cos(2.0 * PI * (soap_center_freq_/sr_));
+
+    // tangent bandwidth
+    float tf = std::tan(PI * (soap_bandwidth_/sr_));
+
+    // coefficient     
+    float c = (tf - 1.0)/(tf + 1.0);                              
+
+    in_0_ = in;   
+
+    all_output_ = -c*in_0_ + (d - d*c)*din_1_ + din_2_ - (d - d*c)*dout_1_ + c*dout_2_;
+
+    // move samples in delay for next sample
+    din_2_ = din_1_;
+    din_1_ = in_0_;
+    dout_2_ = dout_1_;
+    dout_1_ = all_output_;
+
+    // make factor -1.0 to create a bandpass
+    out_bandpass_ =  (in_0_ + all_output_ * -1.0) * 0.5;       
+
+    // make factor +1.0 to create a bandreject 
+    out_bandreject_ =  (in_0_ + all_output_ * 0.99) * 0.5;          
+
+    return;       
+}
+
+void Soap::SetCenterFreq(float f)
+{
+    soap_center_freq_ = f;
+    return;
+}
+
+void Soap::SetFilterBandwidth(float b) {
+    soap_bandwidth_ = b;
+    return;
+}

Source/Filters/soap.h

@@ -0,0 +1,61 @@
+#pragma once
+
+/** Second Order All Pass Filter
+
+This is from Tom Erbe's synth notes. The filter
+can be configured to be a band pass or band reject
+
+Ported by: Brian Tice
+*/
+class Soap
+{
+
+    public:
+        Soap() {}
+        ~Soap() {}
+
+        /** Initializes the filter
+            float sample_rate - sample rate of the audio engine being run, and the frequency that the Process function will be called.
+        */
+        void Init(float sample_rate);
+
+        /** 
+            Process the input signal, updating all of the outputs
+        */
+        void Process(float in);
+
+        /** 
+            Sets the center frequency of the filter. 
+        */
+        void SetCenterFreq(float f);
+
+        /** 
+            Sets the low frequency threshold of the filter. 
+        */
+        void SetFilterBandwidth(float b);
+
+        /** Bandpass output
+            \return bandpass output of the filter
+        */
+        inline float Bandpass() { return out_bandpass_; }
+
+        /** Bandreject output
+            \return bandreject output of the filter
+        */
+        inline float Bandreject() { return out_bandreject_; }
+
+    private:
+        float soap_center_freq_;
+        float soap_bandwidth_;
+        float in_0_;
+        float din_1_;
+        float din_2_;
+        float dout_1_;
+        float dout_2_;
+        float all_output_;
+        float out_bandpass_;
+        float out_bandreject_;
+        float sr_;
+
+
+};

Source/daisysp.h

@@ -60,6 +60,7 @@
 #include "Filters/svf.h"
 #include "Filters/tone.h"
 #include "Filters/fir.h"
+#include "Filters/soap.h"
 
 /** Noise Modules */
 #include "Noise/clockednoise.h"