changeset 533:2ec36efb2c52 prerelease

Added tremolo to audio examples.

--- a/examples/01-Basics/minimal/render.cpp	Thu Jun 23 20:41:22 2016 +0100
+++ b/examples/01-Basics/minimal/render.cpp	Thu Jun 23 21:17:16 2016 +0100
@@ -95,7 +95,7 @@
 ------------------
 `setup()`, `render()` and `cleanup()` each take the same arguments. These are:
 
-`0ext *context`
+`BelaContext *context`
 `void *userData`
 
 These arguments are pointers to data structures. The main one that's used is 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/examples/04-Audio/tremolo/render.cpp	Thu Jun 23 21:17:16 2016 +0100
@@ -0,0 +1,107 @@
+/*
+ ____  _____ _        _    
+| __ )| ____| |      / \   
+|  _ \|  _| | |     / _ \  
+| |_) | |___| |___ / ___ \ 
+|____/|_____|_____/_/   \_\
+
+The platform for ultra-low latency audio and sensor processing
+
+http://bela.io
+
+A project of the Augmented Instruments Laboratory within the
+Centre for Digital Music at Queen Mary University of London.
+http://www.eecs.qmul.ac.uk/~andrewm
+
+(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
+	Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
+	Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.
+
+The Bela software is distributed under the GNU Lesser General Public License
+(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
+*/
+
+#include <Bela.h>
+#include <cmath>
+
+float gFrequency = 4.0;
+float gPhase;
+float gInverseSampleRate;
+
+bool setup(BelaContext *context, void *userData)
+{
+
+	gInverseSampleRate = 1.0 / context->audioSampleRate;
+	gPhase = 0.0;
+
+	return true;
+}
+
+void render(BelaContext *context, void *userData)
+{
+	// Nested for loops for audio channels
+	for(unsigned int n = 0; n < context->audioFrames; n++) {
+	
+		// Generate a sinewave with frequency set by gFrequency
+		// and amplitude from -0.5 to 0.5
+		float lfo = sinf(gPhase) * 0.5;
+		// Keep track and wrap the phase of the sinewave
+		gPhase += 2.0 * M_PI * gFrequency * gInverseSampleRate;
+		if(gPhase > 2.0 * M_PI)
+			gPhase -= 2.0 * M_PI;
+
+		for(unsigned int channel = 0; channel < context->audioChannels; channel++) {
+		    // Read the audio input and half the amplitude
+		    float input = audioRead(context, n, channel) * 0.5;
+			// Write to audio output the audio input multiplied by the sinewave
+			audioWrite(context, n, channel, (input*lfo));
+			
+		}
+	}
+	
+	// Nested for loops for analog channels
+	for(unsigned int n = 0; n < context->analogFrames; n++) {
+		for(unsigned int ch = 0; ch < context->analogChannels; ch++) {
+			// Read analog channel 0 and map the range from 0-1 to 0.25-20
+			// use this to set the value of gFrequency
+			gFrequency = map(analogRead(context, n, 0), 0.0, 1.0, 0.25, 20.0);
+		
+		}
+	}
+	
+}
+
+void cleanup(BelaContext *context, void *userData)
+{
+
+}
+
+
+/**
+\example tremolo/render.cpp
+
+A simple tremolo effect
+-----------------------
+
+This sketch demonstrates how to make a simple tremolo effect with one potiometer to
+control the rate of the effect. A tremolo effect is a simple type of amplitude modulation
+where the amplitude of one signal is continuous modulated by the amplitude of another.
+This is achieved by multiplying to signals together.
+
+In this example we want to create a tremolo effect like that you would find in a guitar
+effects box so our first signal will be our audio input into which we could plug a guitar
+or external sound source. This will be our 'carrier' signal.
+
+The second signal that we will use, the 'modulator', will be a low freqeuncy oscillator (LFO),
+in this case a sinetone which we will generate in the same way as the 01-Basic/sinetone example. 
+The frequency of this sinetone is determined by a global variable, `gFrequency`. Again, the 
+sinetone is produced by incrementing the phase of a sine function on every audio frame.
+
+In `render()` you'll see two nested for loop structures, one for audio and the other for the 
+analogs. You should be pretty familiar with this structure by now. In the first of these for loops
+we deal with all the audio -- in the second with reading the analog input channels. We read the 
+value of analog input 0 and map it to an appropriate range for controlling the frequency
+of the sine tone.
+
+The lfo is then mulitplied together with the audio input and sent to the audio output.
+*/