A voltage-controlled filter (VCF) is an electronic circuit commonly found in synthesizers and audio equipment. It is used to shape the frequency content of an audio signal by selectively allowing certain frequencies to pass through while attenuating others. The VCF is controlled by a control voltage (CV) input, allowing it to be dynamically adjusted in real-time.
The main function of a VCF is to alter the timbre or tonal characteristics of an audio signal. It is often used to create various filtering effects such as low-pass, high-pass, band-pass, and notch filters. Here's a brief explanation of these filter types:
Low-pass filter (LPF): Allows frequencies below a certain cutoff frequency to pass through while attenuating higher frequencies. It effectively reduces the brightness or sharpness of a sound, creating a warmer or smoother effect.
High-pass filter (HPF): Allows frequencies above a certain cutoff frequency to pass through while attenuating lower frequencies. It can be used to remove unwanted low-frequency components from a signal, emphasizing higher harmonics.
Band-pass filter (BPF): Allows a specific range of frequencies to pass through, attenuating both lower and higher frequencies. This filter type is useful for isolating a specific band of frequencies in a signal.
Notch filter: Attenuates a narrow band of frequencies around a specific center frequency, effectively creating a "notch" in the frequency response curve. It is often used to remove unwanted interference or to create interesting audio effects.
The CV input on a VCF allows external devices or modulation sources (such as an envelope generator, LFO, or keyboard controller) to dynamically control the cutoff frequency of the filter. By modulating the VCF's cutoff frequency, users can achieve expressive and dynamic sound shaping.
Voltage-controlled filters are a fundamental building block in analog and modular synthesizers and have also been emulated in digital synthesizers and audio processing software. They play a crucial role in sculpting sound and are an essential tool for sound designers and musicians seeking to explore creative audio manipulation.