A “bandpass filter” is a module or function within a module that selectively passes a specific range of frequencies while attenuating (reducing) the frequencies outside of this range. The bandpass filter has two main parameters: the center or cutoff frequency and the bandwidth.
The center or cutoff frequency determines the midpoint of the frequency range that the filter allows to pass through, while the bandwidth defines the width of the frequency range. A narrow bandwidth results in a more selective filter, allowing only a small range of frequencies to pass, while a wider bandwidth permits a broader range of frequencies.
Bandpass filters are commonly used in modular synthesis to sculpt and shape the harmonic content of audio signals, isolating specific frequency bands and creating unique timbres. By modulating the cutoff frequency and bandwidth with control voltages (CV) from sources like LFOs, sequencers, or envelope generators, musicians can achieve dynamic and evolving sounds that change over time.