Add Bitcrusher effect (thanks Pensive)

https://github.com/PaulStoffregen/Audio/pull/119

Audio.h

 #include "analyze_peak.h"
 #include "control_sgtl5000.h"
 #include "control_wm8731.h"
+#include "effect_bitcrusher.h"
 #include "effect_chorus.h"
 #include "effect_fade.h"
 #include "effect_flange.h"

effect_bitcrusher.cpp

+/* Audio Library for Teensy 3.X
+ * Copyright (c) 2014, Jonathan Payne (jon@jonnypayne.com)
+ * Based on Effect_Fade by Paul Stoffregen
+ * Also samplerate reduction based on Pete Brown's bitcrusher here: 
+ * http://10rem.net/blog/2013/01/13/a-simple-bitcrusher-and-sample-rate-reducer-in-cplusplus-for-a-windows-store-app
+ *
+ * Development of this audio library was funded by PJRC.COM, LLC by sales of
+ * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
+ * open source software by purchasing Teensy or other PJRC products.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice, development funding notice, and this permission
+ * notice shall be included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "effect_bitcrusher.h"
+
+void AudioEffectBitcrusher::update(void)
+{
+	audio_block_t *block;
+	uint32_t i,j;
+	uint32_t sampleSquidge, sampleSqueeze; //squidge is bitdepth, squeeze is for samplerate
+			
+	if (crushBits == 16 && sampleStep <= 1) {
+		// nothing to do. Output is sent through clean, then exit the function
+		block = receiveReadOnly();
+		if (!block) return;
+		transmit(block);
+		release(block);
+		return;
+	}
+	// start of processing functions. Could be more elegant based on external
+	// functions but left like this to enable code optimisation later.
+	block = receiveWritable();
+	if (!block) return;
+
+	if (sampleStep <= 1) { //no sample rate mods, just crush the bitdepth.
+		for (i=0; i < AUDIO_BLOCK_SAMPLES; i++) {
+			// shift bits right to cut off fine detail sampleSquidge is a
+			// uint32 so sign extension will not occur, fills with zeroes.
+			sampleSquidge = block->data[i] >> (16-crushBits);
+			// shift bits left again to regain the volume level.
+			// fills with zeroes.
+		 	block->data[i] = sampleSquidge << (16-crushBits);
+		}
+	} else if (crushBits == 16) { //bitcrusher not being used, samplerate mods only.
+		i=0;
+		while (i < AUDIO_BLOCK_SAMPLES) {
+			// save the root sample. this will pick up a root
+			// sample every _sampleStep_ samples.
+			sampleSqueeze = block->data[i];
+			for (int j = 0; j < sampleStep && i < AUDIO_BLOCK_SAMPLES; j++) {
+ 				// for each repeated sample, paste in the current
+				// root sample, then move onto the next step.
+				block->data[i] = sampleSqueeze;
+				i++;
+			}
+		}
+	} else {           //both being used. crush those bits and mash those samples.
+		i=0;
+		while (i < AUDIO_BLOCK_SAMPLES) {
+			// save the root sample. this will pick up a root sample
+			// every _sampleStep_ samples.
+			sampleSqueeze = block->data[i];
+			for (int j = 0; j < sampleStep && i < AUDIO_BLOCK_SAMPLES; j++) {
+ 				// shift bits right to cut off fine detail sampleSquidge
+				// is a uint32 so sign extension will not occur, fills
+				// with zeroes.
+				sampleSquidge = sampleSqueeze >> (16-crushBits);
+ 				// shift bits left again to regain the volume level.
+				// fills with zeroes. paste into buffer sample +
+				// sampleStep offset.
+				block->data[i] = sampleSquidge << (16-crushBits);
+				i++;
+			}
+		}
+	}
+	transmit(block);
+	release(block);
+}
+
+#if 0
+void AudioEffectBitcrusher::updateCrush(uint8_t xxcrushBits, uint32_t xxsampleRate )
+{
+	__disable_irq();
+	if (xxcrushBits >= 16) { //too high a bitdepth or specifying full 16 bit range?
+		crushBits = 16; // this will simply passthrough the crusher clean
+	} else if(xxcrushBits >= 1) { // anywhere between 1 and 15, send it through to the Squidger.
+		crushBits = xxcrushBits;
+	} else {
+		crushBits =1; // now lets be honest, crushing to 0 bits is going to be a mute command. send a 1 through instead.
+	} 
+
+	if (xxsampleRate >=44100) {// maximum sample rate to be 44100
+		sampleRate = 44100; //thats that
+	} else if(xxsampleRate >= 1) { // anywhere between 1 and 44100, send it through to the Squeezer.
+		sampleRate = xxsampleRate; 
+		sampleStep = 44100 / sampleRate; // calcualte the number of samples to duplicate as we reduce the samplerate.
+	} else {
+		sampleRate = 1;
+		sampleStep = 44100 / sampleRate; // calcualte the number of samples to duplicate as we reduce the samplerate.
+	}
+	__enable_irq();
+}
+#endif
+
+

effect_bitcrusher.h

+/* Audio Library for Teensy 3.X
+ * Copyright (c) 2014, Jonathan Payne (jon@jonnypayne.com)
+ * Based on Effect_Fade by Paul Stoffregen
+
+ * Development of this audio library was funded by PJRC.COM, LLC by sales of
+ * Teensy and Audio Adaptor boards.  Please support PJRC's efforts to develop
+ * open source software by purchasing Teensy or other PJRC products.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice, development funding notice, and this permission
+ * notice shall be included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef effect_bitcrusher_h_
+#define effect_bitcrusher_h_
+
+#include "AudioStream.h"
+
+class AudioEffectBitcrusher : public AudioStream
+{
+public:
+	AudioEffectBitcrusher(void)
+	  : AudioStream(1, inputQueueArray) {}
+	void bits(uint8_t b) {
+		if (b > 16) b = 16;
+		else if (b == 0) b = 1;
+		crushBits = b;
+	}
+        void sampleRate(float hz) {
+		int n = (AUDIO_SAMPLE_RATE_EXACT / hz) + 0.5;
+		if (n < 1) n = 1;
+		else if (n > 64) n = 64;
+		sampleStep = n;
+	}
+	virtual void update(void);
+	
+private:
+	uint8_t crushBits; // 16 = off
+	uint8_t sampleStep; // the number of samples to double up. This simple technique only allows a few stepped positions.
+	audio_block_t *inputQueueArray[1];
+};
+
+#endif

examples/Effects/Bitcrusher/Bitcrusher.ino

+#include <Audio.h>
+#include <Wire.h>
+#include <SPI.h>
+#include <SD.h>
+#include <SerialFlash.h>
+#include <Bounce.h>
+
+// Bitcrusher example by Jonathan Payne (Pensive) jon@jonnypayne.com
+// No rights reserved. Do what you like with it.
+
+// Create the Audio components.
+AudioPlaySdWav      playWav1;       //this will play a looping demo file
+AudioOutputI2S      headphones;           // and it will come out of the headphone socket.
+
+//Audio Effect BitCrusher defs here
+AudioEffectBitcrusher   left_BitCrusher;
+AudioEffectBitcrusher   right_BitCrusher;
+
+// Create Audio connections between the components
+AudioConnection         patchCord1(playWav1, 0, left_BitCrusher, 0);
+AudioConnection         patchCord2(playWav1, 1, right_BitCrusher, 0);
+AudioConnection         patchCord3(left_BitCrusher, 0, headphones, 0);
+AudioConnection         patchCord4(right_BitCrusher, 0, headphones, 1);
+
+// Create an object to control the audio shield.
+//
+AudioControlSGTL5000 audioShield;
+
+// Bounce objects to read six pushbuttons (pins 0-5)
+//
+Bounce button0 = Bounce(0, 5); // cycles the bitcrusher through all bitdepths
+Bounce button1 = Bounce(1, 5); //cycles the bitcrusher through some key samplerates
+Bounce button2 = Bounce(2, 5); // turns on the compressor (or "Automatic Volume Leveling")
+
+unsigned long SerialMillisecondCounter;
+
+//BitCrusher
+int current_CrushBits = 16; //this defaults to passthrough.
+int current_SampleRate = 44100; // this defaults to passthrough.
+
+//Compressor
+boolean compressorOn = false; // default this to off.
+
+void setup() {
+  // Configure the pushbutton pins for pullups.
+  // Each button should connect from the pin to GND.
+  pinMode(0, INPUT_PULLUP);
+  pinMode(1, INPUT_PULLUP);
+  pinMode(2, INPUT_PULLUP);
+  Serial.begin(38400); // open the serial
+
+  // Audio connections require memory to work.  For more
+  // detailed information, see the MemoryAndCpuUsage example
+  AudioMemory(40); //this is WAY more tha nwe need
+
+  // turn on the output
+  audioShield.enable();
+  audioShield.volume(0.7);
+
+  // by default the Teensy 3.1 DAC uses 3.3Vp-p output
+  // if your 3.3V power has noise, switching to the
+  // internal 1.2V reference can give you a clean signal
+  //dac.analogReference(INTERNAL);
+
+  // reduce the gain on mixer channels, so more than 1
+  // sound can play simultaneously without clipping
+
+  //SDCard Initialise
+  SPI.setMOSI(7);
+  SPI.setSCK(14);
+  if (!(SD.begin(10))) {
+    // stop here, but print a message repetitively
+    while (1) {
+      Serial.println("Unable to access the SD card");
+      delay(500);
+    }
+  }
+  // Bitcrusher
+  left_BitCrusher.bits(current_CrushBits); //set the crusher to defaults. This will passthrough clean at 16,44100
+  left_BitCrusher.sampleRate(current_SampleRate); //set the crusher to defaults. This will passthrough clean at 16,44100
+  right_BitCrusher.bits(current_CrushBits); //set the crusher to defaults. This will passthrough clean at 16,44100
+  right_BitCrusher.sampleRate(current_SampleRate); //set the crusher to defaults. This will passthrough clean at 16,44100
+  //Bitcrusher
+
+
+  /* Valid values for dap_avc parameters
+
+	maxGain; Maximum gain that can be applied
+	0 - 0 dB
+	1 - 6.0 dB
+	2 - 12 dB
+	
+	lbiResponse; Integrator Response
+	0 - 0 mS
+	1 - 25 mS
+	2 - 50 mS
+	3 - 100 mS
+	
+	hardLimit
+	0 - Hard limit disabled. AVC Compressor/Expander enabled.
+	1 - Hard limit enabled. The signal is limited to the programmed threshold (signal saturates at the threshold)
+	
+	threshold
+	floating point in range 0 to -96 dB
+	
+	attack
+	floating point figure is dB/s rate at which gain is increased
+	
+	decay
+	floating point figure is dB/s rate at which gain is reduced
+*/
+// Initialise the AutoVolumeLeveller
+  audioShield.autoVolumeControl(1, 1, 0, -6, 40, 20); // **BUG** with a max gain of 0, turning the AVC off leaves a hung AVC problem where the attack seems to hang in a loop. with it set 1 or 2, this does not occur.
+  audioShield.autoVolumeDisable();
+  audioShield.audioPostProcessorEnable();
+
+  SerialMillisecondCounter = millis();
+}
+
+int val; //temporary variable for memory usage reporting.
+
+void loop() {
+
+  if (millis() - SerialMillisecondCounter >= 5000) {
+    Serial.print("Proc = ");
+    Serial.print(AudioProcessorUsage());
+    Serial.print(" (");
+    Serial.print(AudioProcessorUsageMax());
+    Serial.print("),  Mem = ");
+    Serial.print(AudioMemoryUsage());
+    Serial.print(" (");
+    Serial.print(AudioMemoryUsageMax());
+    Serial.println(")");
+    SerialMillisecondCounter = millis();
+    AudioProcessorUsageMaxReset();
+    AudioMemoryUsageMaxReset();
+  }
+
+
+  // Update all the button objects
+  button0.update();
+  button1.update();
+  button2.update();
+
+  // Start test sound if it is not playing. This will loop infinitely.
+  if (! (playWav1.isPlaying())){
+    playWav1.play("SDTEST1.WAV"); // http://www.pjrc.com/teensy/td_libs_AudioDataFiles.html
+  }
+
+  if (button0.fallingEdge()) {
+    //Bitcrusher BitDepth
+    if (current_CrushBits >= 2) { //eachtime you press it, deduct 1 bit from the settings.
+        current_CrushBits--;
+    } else {
+      current_CrushBits = 16; // if you get down to 1 go back to the top.
+    }
+
+    left_BitCrusher.bits(current_CrushBits);
+    left_BitCrusher.sampleRate(current_SampleRate);
+    right_BitCrusher.bits(current_CrushBits);
+    right_BitCrusher.sampleRate(current_SampleRate);
+    Serial.print("Bitcrusher set to ");
+    Serial.print(current_CrushBits);
+    Serial.print(" Bit, Samplerate at ");
+    Serial.print(current_SampleRate);
+    Serial.println("Hz");
+  }
+
+  if (button1.fallingEdge()) {
+    //Bitcrusher SampleRate // the lowest sensible setting is 345. There is a 128 sample buffer, and this will copy sample 1, to each of the other 127 samples.
+    if (current_SampleRate >= 690) { // 345 * 2, so we can do one more divide
+      current_SampleRate = current_SampleRate / 2; // half the sample rate each time
+    } else {
+      current_SampleRate=44100; // if you get down to the minimum then go back to the top and start over.
+    }
+
+    left_BitCrusher.bits(current_CrushBits);
+    left_BitCrusher.sampleRate(current_SampleRate);
+    right_BitCrusher.bits(current_CrushBits);
+    right_BitCrusher.sampleRate(current_SampleRate);
+    Serial.print("Bitcrusher set to ");
+    Serial.print(current_CrushBits);
+    Serial.print(" Bit, Samplerate at ");
+    Serial.print(current_SampleRate);
+    Serial.println("Hz");
+  }
+
+  if (button2.fallingEdge()) {
+    if (compressorOn) {
+      //turn off compressor
+      audioShield.autoVolumeDisable();
+      compressorOn = false;
+    } else {
+      //turn on compressor
+      audioShield.autoVolumeEnable();
+      compressorOn = true;
+    }
+    Serial.print("Compressor: ");
+    Serial.println(compressorOn);
+  }
+}
+

gui/list.html

 </script>
 
 
+<script type="text/javascript">
+    RED.nodes.registerType('AudioEffectBitcrusher',{
+    shortName: "bitcrusher",
+        inputs:1,
+        outputs:1,
+        category: 'effect-function',
+        color:"#E6E0F8",
+        icon: "arrow-in.png"
+    });
+</script>
+<script type="text/x-red" data-help-name="AudioEffectBitcrusher">
+    <h3>Summary</h3>
+    <p>Reduce the samplerate and/or bitdepth of a source signal, resulting in
+		a distorted sound.</p>
+    <h3>Audio Connections</h3>
+    <table class=doc align=center cellpadding=3>
+        <tr class=top><th>Port</th><th>Purpose</th></tr>
+        <tr class=odd><td align=center>In 0</td><td>Signal Input</td></tr>
+        <tr class=odd><td align=center>Out 0</td><td>Signal Output</td></tr>
+    </table>
+    <h3>Parameters</h3>
+    <p class=func><span class=keyword>bits</span>(xcrushBits);</p>
+    <p class=desc>xcrushBits sets the bitdepth, from 1 to 16. A Value of 16
+    does not crush the bitdepth, and is effectively a passthru for this part
+    of the function.</p>
+
+    <p class=func><span class=keyword>sampleRate</span>(xsampleRate);</p>
+
+    <p class=desc>xsampleRate sets the frequency, from 1 to 44100Hz, however it
+    works in integer steps so you will only really get a handful of results from
+    the many samplerates you can pass. 44100 is passthru.</p>
+
+    <p class=desc>set xbitDepth to 16 and xsampleRate to 44100 to pass audio
+    	through without any Bitcrush effect.</p>
+    <h3>Examples</h3>
+    <p class=exam>File &gt; Examples &gt; Audio &gt; Effects &gt; Bitcrusher
+    </p>
+    <h3>Notes</h3>
+    <p>Needs a lot of improvement. Options for anti-aliasing would be nice in
+    the future, but for now, it's rough, it's dirty and it sounds a bit like
+    Nine Inch Nails.
+    </p>
+    <p><a href="http://www.pjrc.com/teensy/td_libs_AudioProcessorUsage.html" target="_blank">AudioNoInterrupts()</a>
+        should be used when changing
+        settings on multiple objects, so all changes always take effect
+        at the same moment.
+    </p>
+</script>
+<script type="text/x-red" data-template-name="AudioEffectBitcrusher">
+    <div class="form-row">
+        <label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
+        <input type="text" id="node-input-name" placeholder="Name">
+    </div>
+</script>
+
+
+
 
 
 <script type="text/javascript">