At a synthesizer's core, the oscillator is a key figure, as it's the component that allows the system to create sound. This circuit produces the electronic signal that is fed through the rest of your system and manipulated by using other pieces of modular synth gear. While building a synth requires at least one oscillator, there is no limit to how many you can add to your build-out. Having a variety of oscillators offers multiple choices in voicing, giving users the ability to create one-of-a-kind sounds by mixing a combination of waveforms.
The Voltage Controlled Amplifier, or VCA, is the last module standing before your signal hits the synthesizer's output. Fundamental to a synth rig producing amplified sound, the most common use of a VCA is controlling the volume of input signals and the gain level of the output. Yet, these modules often serve a multitude of purposes, as users are able to attenuate levels and create deep swells, as the amplifier can be controlled via other modules.
Modular synthesizers are meant to create some of the most interesting sounds ever heard, but if it weren't for Envelope Generators, your system could become extremely boring fast. These dynamic modules are used (with some help from a keyboard or controller), to generate a control voltage signal. Using the standard controls typical to most EGs (Attack, Decay, Sustain and Release), users can make significant changes to sounds being created and mimic everything from kick drums to short pads.
Further sculpting of your synthesizer's sound will be predominantly controlled by filter modules. Synth players can alter other aspects of their signal (aside from pitch and intensity), by using common filters like Low-Pass, High-Pass, Comb, Band-Pass and Notch. Just as its name implies, these modules offer users a plethora of options for blocking some frequencies and allowing others to pass through. Thus, by having multiple modules that affect different frequency levels, you'll be able to make a wider range of sounds with your modular synth.
Capable of creating many different effects with your modular synth's signal, Low-Frequency Oscillators were created by accident, but have since become a staple of the synth world. While the main oscillator circuits create the initial audio signals, an LFO operates at a lower frequency and allows users to build upon the intricacy of their sound. By manipulating an LFO, synth players can create basic effects like phase, vibrato, tremolo and more.