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High-pass filter

A High-pass filter passes 'high' frequencies fairly well, but attenuates 'low' frequencies. 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.

The simplest 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% of the input.

Such a circuit would be used in combination with a Tweeter, Loudspeaker.