Voltage control defines the synthesizer and differentiates it from separate components such as amplifiers, oscillators, filters, etc.
The synthesizer generates and modifies electronic waveforms in the audio spectrum. Unlike traditional acoustic instruments such as violin, percussion, etc., the electronic medium is highly flexible. Instead of physically altering the material of typical instruments, such as bracing a guitar to change its resonance, synthesizers can only need to change electrical or digital values to make new sounds. This makes them much more fluent than traditional acoustic instruments. It also means they can create sounds that aren't physically possible. Finally, players can explore the variety of sounds much more quickly and easily.
When synthesizers first entered the underground music scene in the early 1960s, constructing them was difficult. Knowledge of engineering specific to making sound waves was scarce and components were not ideal for making music. Furthermore, people didn't have references - they didn't know what they wanted to build. In the 21st century, however, synthesizer design is commonplace and many sources of information from people to websites share the basic as well as the secrets. It's even possible to construct playable synthesizer instruments in your own home with less than $100 in parts.
- Synthesizer , Wikipedia