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RC Filter

Minimal low-pass or high-pass filter.

Description

A simple low-pass or high-pass filter with no feedback is frequently required for many purposes. Commonly for EQ, DC offset removal, thump/ULF reduction, ringing reduction and band limiting or shaping in effect chains or during mastering.

Screenshot

RC Filter screenshot

Parameters

Frequency
The cutoff frequency for the filter. At Fc the amplitude is reduced by half the slope of the filter.
Mode
The filter type and slope, including low, high and 6, 12, 18, 24 dB.

Comments

The simple RC circuit is considered the most basic analog filter. It is solely a single resistor and capacitor. A low-pass filter is formed by placing the resistor as the input and capacitor bypassing the output to ground. A high-pass filter is formed by exchanging the two components.

An ideal circuit has no feedback, provides a monotonic frequency and phase slope with no peaks or ripples and has no effect on DC/inf amplitude. This makes the RC filter the most minimal filter type with the least impact on timbre; excepting an inaudible bypass or all-pass filter.

An RC filter is the best solution where the goal is to apply a filtering effect with absolutely minimal impact. An RC high-pass filter for DC offset removal or low-frequency content reduction is a common application.

Higher order filters including those with feedback such as a Butterworth filter are better suited to more complex aims. A Butterworth may be used to minimize impact within the pass-band by trading away overall audibility. The RC filter avoids the complications of such a trade-off by doing the least possible in the most simple way.