# 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

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High_pass_filter.png
A passive, analog, first-order high-pass filter

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, or half the square root of 2) of the input:

[itex] f = {1 \over 2 \pi R C} [itex]

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.

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