High-pass filter

A high-pass filter passes 'high' frequencies fairly well, but attenuates 'low' frequencies. Therefore it is also called a low-cut filter or bass-cut filter. The term rumble filter is sometimes used. A high-pass filter is the opposite of a low-pass filter. See also bandpass filter.

Hence it is useful as a filter to block any unwanted low frequency components of a complex signal whilst passing the higher frequencies. Of course, the meanings of 'low' and 'high' frequencies are relative, actually desired values would influence choice of component values in an implementation.

Implementation

The simplest electronic high-pass filter consists of a capacitor in series with the signal path in conjunction with a resistor in parallel with the signal path. The resistance times the capacitance (R×C) is the time constant; its reciprocal is the cutoff frequency, at which the output voltage is 70.7% (or -3 dB) of the input:

<math> f = {1 \over 2 \pi R C} <math>

Where f is in hertz, R is in ohms, and C is in farads.

Applications

Such a filter could be used to direct high frequencies to a tweeter speaker while blocking bass signals which could interfere with or damage the speaker. A low-pass filter could simultaneously be used to direct low frequencies to the woofer.

See also

• DSL splitter