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