Added tests for DC-filter.

DCBlock.h

@@ -0,0 +1,46 @@
+// From "git clone --recursive https://github.com/SpotlightKid/ykchorus.git"
+/*
+    ==============================================================================
+    This file is part of Tal-NoiseMaker by Patrick Kunz.
+
+    Copyright(c) 2005-2010 Patrick Kunz, TAL
+    Togu Audio Line, Inc.
+    http://kunz.corrupt.ch
+
+    This file may be licensed under the terms of of the
+    GNU General Public License Version 2 (the ``GPL'').
+
+    Software distributed under the License is distributed
+    on an ``AS IS'' basis, WITHOUT WARRANTY OF ANY KIND, either
+    express or implied. See the GPL for the specific language
+    governing rights and limitations.
+
+    You should have received a copy of the GPL along with this
+    program. If not, go to http://www.gnu.org/licenses/gpl.html
+    or write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+    ==============================================================================
+ */
+
+#if !defined(__DCBlock_h)
+#define __DCBlock_h
+
+class DCBlock {
+public:
+    float inputs, outputs, lastOutput;
+
+    DCBlock() {
+        lastOutput = inputs = outputs = 0.0f;
+    }
+
+    ~DCBlock() {}
+
+    inline void tick(float *sample, float cutoff) {
+        outputs     = *sample - inputs + (0.999f - cutoff * 0.4f) * outputs;
+        inputs      = *sample;
+        lastOutput  = outputs;
+        *sample     = lastOutput;
+    }
+};
+
+#endif

effect_modulated_delay.cpp

@@ -26,6 +26,8 @@
 #include "arm_math.h"
 #include "effect_modulated_delay.h"
 #include "config.h"
+#include "DCBlock.h"
+#include "limits.h"
 
 extern config_t configuration;
 
@@ -63,6 +65,8 @@ boolean AudioEffectModulatedDelay::begin(short *delayline, int d_length)
   set_modulator_filter_coeffs();
   modulator_filter_data = {1, modulator_filter_state, modulator_filter_coeffs};
 
+  dcBlock = new DCBlock();
+
   return (true);
 }
 
@@ -141,6 +145,11 @@ void AudioEffectModulatedDelay::update(void)
           cb_mod_index_neighbor = cb_mod_index + 1;
         *bp = round(float(_delayline[cb_mod_index_neighbor]) * mod_fraction + float(_delayline[cb_mod_index]) * (1.0 - mod_fraction));
       }
+
+      // simple Test for DC filter
+      float bp_f=*bp/SHRT_MAX;
+      dcBlock->tick(&bp_f, 0.01f);
+      *bp=bp_f*SHRT_MAX;
       
       // push the pointers forward
       bp++; // next audio data

effect_modulated_delay.h

@@ -27,6 +27,7 @@
 #include "Arduino.h"
 #include "AudioStream.h"
 #include "config.h"
+#include "DCBlock.h"
 
 #define MODULATION_MAX_FACTOR 0.75
 
@@ -59,6 +60,7 @@ class AudioEffectModulatedDelay :
     arm_biquad_casd_df1_inst_f32 modulator_filter_data;
     float32_t modulator_filter_state[4];
     float32_t modulator_filter_coeffs[5];
+    DCBlock *dcBlock;
 };
 
 #endif

mozzi/DCfilter.h

@@ -0,0 +1,89 @@
+/*
+ * DCfilter.h
+ *
+ * Copyright 2012 Tim Barrass.
+ *
+ * This file is part of Mozzi.
+ *
+ * Mozzi is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
+ *
+ */
+
+#ifndef DCFILTER_H
+#define DCFILTER_H
+
+/*
+tb2010 adapted from:
+robert bristow-johnson, DSP Trick: Fixed-Point DC Blocking Filter with Noise-Shaping
+http://www.dspguru.com/book/export/html/126
+
+y[n] = x[n] - x[n-1] + a * y[n-1]
+
+Where y[n] is the output at the current time n, and x[n] is the input at the current time n.
+
+also, see DC Blocker Algorithms, http://www.ingelec.uns.edu.ar/pds2803/materiales/articulos/04472252.pdf
+ */
+
+/**
+A DC-blocking filter useful for highlighting changes in control signals.
+The output of the filter settles to 0 if the incoming signal stays constant.  If the input changes, the
+filter output swings to track the change and eventually settles back to 0.
+*/
+class DCfilter
+{
+public:
+/**
+Instantiate a DC-blocking filter.
+@param pole sets the responsiveness of the filter,
+how long it takes to settle to 0 if the input signal levels out at a constant value.
+*/
+	DCfilter(float pole):acc(0),prev_x(0),prev_y(0)
+	{
+		A = (int)(32768.0*(1.0 - pole));
+	}
+
+/*  almost original
+	// timing: 20us
+	int next(int x)
+	{
+		setPin13High();
+		acc   -= prev_x;
+		prev_x = (long)x<<15;
+		acc   += prev_x;
+		acc   -= A*prev_y;
+		prev_y = acc>>15;               // quantization happens here
+		int filtered = (int)prev_y;
+		// acc has y[n] in upper 17 bits and -e[n] in lower 15 bits
+		setPin13Low();
+		return filtered;
+	}
+	*/
+
+	/**
+	Filter the incoming value and return the result.
+	@param x the value to filter
+	@return filtered signal
+	*/
+	// timing :8us
+	inline
+	int next(int x)
+	{
+		acc += ((long)(x-prev_x)<<16)>>1;
+		prev_x = x;
+		acc   -= (long)A*prev_y; 	// acc has y[n] in upper 17 bits and -e[n] in lower 15 bits
+		prev_y = (acc>>16)<<1; // faster than >>15 but loses bit 0
+		if (acc & 32784) prev_y += 1; // adds 1 if it was in the 0 bit position lost in the shifts above
+		return prev_y;
+	}
+
+private:
+	long acc;
+	int prev_x, prev_y,A;
+};
+
+/**
+@example 05.Control_Filters/DCFilter/DCFilter.ino
+This example demonstrates the DCFilter class.
+*/
+
+#endif        //  #ifndef DCFILTER_H

mozzi/DCfilter.ino

@@ -0,0 +1,50 @@
+/* Example of filtering an analog input to remove DC bias,
+    using Mozzi sonification library.
+
+    Demonstrates DCfilter(), DC-blocking filter useful for
+    highlighting changes in control signals.
+    The output of the filter settles to 0 if the incoming signal stays constant.
+    If the input changes, the filter output swings to track the change and
+    eventually settles back to 0.
+
+		Mozzi documentation/API
+		https://sensorium.github.io/Mozzi/doc/html/index.html
+
+		Mozzi help/discussion/announcements:
+    https://groups.google.com/forum/#!forum/mozzi-users
+
+    Tim Barrass 2013, CC by-nc-sa.
+
+*/
+
+#include <MozziGuts.h>
+#include <DCfilter.h>
+
+int sensorPin = A0;
+
+DCfilter dcFiltered(0.9); // parameter sets how long the filter takes to settle
+
+void setup() {
+  //Serial.begin(9600); // for Teensy 3.1, beware printout can cause glitches
+  Serial.begin(115200);
+  startMozzi();
+}
+
+
+void updateControl(){
+  // read the value from the sensor:
+  int sensorValue = mozziAnalogRead(sensorPin);
+  Serial.print(sensorValue);
+  Serial.print("  Filtered = ");
+  Serial.println(dcFiltered.next(sensorValue));
+}
+
+
+int updateAudio(){
+  return 0;
+}
+
+
+void loop(){
+  audioHook();
+}