Voltage-controlled refers to a type of electronic component or circuit that changes its operation based on an input voltage. In synthesizers and other audio equipment, this principle is key to generating and manipulating sound. Voltage-controlled elements include voltage-controlled oscillators (VCOs), voltage-controlled filters (VCFs), and voltage-controlled amplifiers (VCAs). These components are fundamental in analogue synthesizers, where different voltages are used to control aspects like pitch, timbre, and loudness.

For example, in a voltage-controlled oscillator, the frequency of the sound wave (and thus its pitch) changes based on the control voltage applied. Similarly, in a voltage-controlled filter, the cutoff frequency can be adjusted dynamically by varying the input voltage. This voltage-control mechanism allows for highly expressive and dynamic sound shaping. It also enables modulators like low-frequency oscillators (LFOs) and envelope generators to interact with these components to create effects such as vibrato, tremolo, filter sweeps, and more.