Audio Toolbox™ supports several approaches for the development of audio processing algorithms. Two common approaches include procedural programming using MATLAB® scripts and object-oriented programming using MATLAB classes. The audio plugin class is the suggested paradigm for developing your audio processing algorithm in Audio Toolbox. See Audio Plugins in MATLAB for a tutorial on the structure, benefits, and uses of audio plugins.
This tutorial presents an existing algorithm developed as a MATLAB script, and then walks through the steps to convert the script to an audio plugin class. Use this tutorial to understand the relationship between procedural programming and object-oriented programming. You can also use this tutorial as a template to convert any audio processing you developed as MATLAB scripts to the audio plugin paradigm.
The MATLAB script has these sections:
Variable Initialization. Variables
are initialized with known values, including the number of samples per
frameSize) for frame-based stream
Audio Stream Loop. Mixes stereo channels into a mono signal. The mono signal is used to create a new stereo signal. Each channel of the new stereo signal oscillates in applied gain between 0 and 2, with a respective 90-degree phase shift.
This tutorial converts a MATLAB script to an audio plugin class in six steps. You begin by creating a skeleton of a basic audio plugin class, and then map sections of the MATLAB script to the audio plugin class.
For an overview of how a MATLAB script is converted to a plugin class, inspect the script to plugin visual mapping. To perform this conversion, walk through the example for explanations and step-by-step instructions.
Begin with the basic skeleton of an audio plugin class. This skeleton is not the minimum required, but a common minimum to create an interesting audio plugin. See Audio Plugins in MATLAB for the minimum requirements to create a basic audio plugin.
Properties allow a plugin to store information across sections of the plugin class definition. If a property has access set to private, the property is not accessible to the end user of a plugin. Variable initialization in a script maps to plugin properties.
A valid plugin must allow input to the
to have a variable frame size. Frame size is determined for each input
frame in the
process method of the plugin. Because
frame size is used only in the
process method, you do
not declare it in the properties section.
A valid audio plugin must allow input to the
method to have a variable sample rate. The
of a plugin is called when the environment changes the sample rate.
Determine the sample rate in the
reset method using the
getSampleRate method inherited from the
audioPlugin base class.
The objects used by a plugin must be declared as properties to be used in multiple sections of the plugin. However, the constructor method of a plugin performs object construction.
Add a constructor method to the methods section of your audio plugin. The constructor method of a plugin has the form:
function plugin = myPluginClassName % Instructions to construct plugin object. end
In this example, you construct the
Cosine objects in the constructor method of the
reset method of a plugin is called every time a new
session is started with the plugin, or when the environment changes sample rate.
reset method to update the
SampleRate property of your
Cosine objects. To query the sample rate, use the
getSampleRate base class method.
The contents of the audio stream loop in a script maps to the
process method of an audio plugin, with these differences:
A valid audio plugin must accept a variable frame size, so frame
size is calculated for every call to the
method. Because frame size is variable, any processing that relies
on frame size must update when input frame size changes.
The environment handles the input and output to the
The plugin interface lets users view the plugin and tune its properties.
PluginInterface as an
audioPluginInterface object that
audioPluginParameter object. The
first argument of
audioPluginParameter is the property you
want to synchronize with a tunable parameter. Choose the display name, label the
units, and set the parameter range. This example uses 0.1 to 10 as a reasonable
range for the
Frequency property. Write code so that during
each call to the
process method, your
Cosine objects are updated with the current frequency
Once your audio plugin class definition is complete: