The “cutoff frequency” (also known as the “filter frequency” or “center frequency”) refers to the frequency point at which the filter starts to attenuate or reduce the amplitude of the input signal’s frequency components. Filters are commonly used in modular synthesis to shape the harmonic content and timbre of sound sources, such as oscillators or noise generators.
The cutoff frequency is a critical parameter for controlling the tonal character of the filtered signal, and it is often adjustable using control knobs, sliders, or voltage control. In voltage-controlled filters (VCFs), the cutoff frequency can be modulated by external control voltage (CV) signals, such as envelopes, LFOs, or sequencers, allowing for dynamic and expressive control over the filter’s response.
Different types of filters, such as low-pass, high-pass, band-pass, and notch filters, have different responses and effects on the input signal based on their cutoff frequency:
- Low-pass filter: The cutoff frequency determines the point above which higher frequencies are attenuated. Lowering the cutoff frequency will result in a darker and more muffled sound, while increasing it will let more high-frequency content pass through.
- High-pass filter: The cutoff frequency determines the point below which lower frequencies are attenuated. Raising the cutoff frequency will result in a thinner and more resonant sound, while decreasing it will let more low-frequency content pass through.
- Band-pass filter: The cutoff frequency represents the center frequency of the band that is allowed to pass through. Adjusting the cutoff frequency will change the range of frequencies that are emphasized or attenuated, effectively sweeping through the frequency spectrum.
- Notch filter: The cutoff frequency represents the center frequency of the notch or band that is being attenuated. Adjusting the cutoff frequency will change the range of frequencies that are suppressed, creating a phasing-like effect on the input signal.
