Screenshot

 

This is a screenshot of the Synthesizer showing the editor panels of a number of loaded plugins, such as the Universal plugin synthesizer. Plugin editor panels are full of knobs and switches and you use these to adjust the way that the synthesizer computes the output sounds. For example, a knob labelled cutoff normally indicates the filter cutoff frequency for a filter such as a lowpass or highpass filter. The default filter type is a lowpass filter, and you can use the cutof knob to adjust how much of the high frequencies that you hear, but if the filter was a highpass filter then it adjusts the amount of low frequencies that you hear. This example of using the cutoff knob and the filter type is just two parameters, but some synths have thousands of parameters, so you can really change the sounds in a lot of ways, since all parameters often affect the other parameters.