# Getting started and setting up processor properties¶

The properties of an object are a way to store data used by the object. There are two types of properties for processors, those which:

• store all the parameters needed to integrate the processor into the framework (e.g., the sampling frequency on which it operates, the number of inputs/outputs, ...)
• store parameter values which are used in the actual processing

When writing the class definition for a new processor, it is only necessary to implement the latter: parameters which are needed in the computation. All parameters needed for the integration of the processor in the framework are already defined in the parent Processor class. Your new processor should inherit this parent class in order to automatically have access to the properties and methods of the parent class. Inheritance in Matlab is indicated by the command < nameOfParentClass following the name of your new class in the first line of its definition.

The new processor class definition should be saved in a .m file that has the same name as the defined class. In the example below, that would be myNewProcessor.m.

There are usually two categories of properties to be implemented for a new processor: external (user-controlled) parameters and internal parameters necessary for the processor but which do not need to be known to the “outside world”.

Note

Only the two types of properties below have been used so far in every processor implementation. However, it is fine to add more if needed for your new processor.

## External parameters controllable by the user¶

External parameters are directly related to the parameters the user can access and change. The actual values for these are stored in a specific object accessible via the .parameters property of the processor. Defining them as individual properties seems redundant, and is therefore optional. However it can be very convenient in order to simplify the access to the parameter value and to make your code more readable.

Instead of storing an actual value, the corresponding processor property should only point to a value in the .parameters object. This will avoid having two different values for the same parameter. To do this, external parameters should be defined as a set of dependent properties. This is indicated by the Dependent = true property attribute. If a property is set to Dependent, then a corresponding “getter” method has to be implemented for it. This will be developed in a following section. For example, if your new processor has two parameters, parA and parB, you can define these as properties as follow:

classdef myNewProcessor < Processor

properties (Dependent = true)
parA;
parB;
end

%...

end


This will allow easier access to these values in your code. For example, myNewProcessor.parA will always give the same output as myNewProcessor.parameters.map('xx_nameTagOfParameterA'), even if the parameter value changes due to feedback. This simplifies greatly the code, particularly when many parameters are involved.

## Internal parameters¶

Internal parameters are sometimes (not always) needed for the functioning of the processor. They are typically used to store internal states of the processor (e.g., to allow continuity in block-based processing), filter instances (if your processor involves filtering), or just intermediate parameter values used to make code more readable.

Because they are “internal” to the processor, these parameters are usually stored as a set of private properties by using the GetAccess = private property attributes. This will virtually make the property invisible and inaccessible to all other objects.