As mentioned before, the Polynomial Equalizer project is a VST3 plugin.

This means that it needs to respect the design pattern provided by the VST3SDK.

The plugin itself is divided into 2 core parts:

a) PluginProcessor

b) PluginController

PluginProcessor

Manages the actual audio processing.

Is called by the host to perform actions on the provided samples.

FFTProcessor

Transforms time-domain samples to frequency-domain data.

Delegates the data to an Equalizer which transforms it by its own definition.

Reconstructs modified audio data.

PolynomialEqualizer

Is an implementation of the abstract Equalizer

Defines its modulation by a polynomial function.

Makes use of user parameters to shape the EQ curve.

PluginController

Keeps track of parameters and states.

Acts as a bridge between the UI and the audio pipeline.

Registers the main VSTGUI view.

VSTGUI

This GUI framework provided by the SDK constructs a view defined in a .uidesc file.

It also intializes custom views with a defined factory class such as EQCurveView which displays a live function graph.

Project diagram

Class diagram

Further possible improvements

The bypass handling could be implemented in a more sturdy way to handle frequent on/off switching without unwanted audio fragmentation.

In the current state the EQ allows for audio mangling for example when the user sets the intensity too high. This is a bit controversial in my opinion. The user probably expects some artifacting when they turn all knobs to the limit. However, some kind of safe mode would be an interesting toggle to implement.