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→High-Pass
==== High-Pass ====
A high-pass filter (EQ) allows high frequencies to pass, but filters out frequencies below a certain point. It can be rather gradual so that as frequencies get lower and lower they get slightly softer and softer until they are inaudible, or it can be rather abrupt, where frequencies above than the cutoff frequency are nearly completely unaffected, but frequencies below the cutoff are completely inaudible. See also: [[#Low-Pass]].
==== Hum ====
Hum, (also known as ground hum), is a constant sound at a fixed frequency, typically 50, 60, or 120 HZ. Its low-frequency, low-overtone nature sounds similar to the vocal technique of humming. It is usually caused by a [[#Ground Loop|ground loop]] but may simply be an artifact of the amplifier's design, requiring transforming AC from its power mains.
==== Impedance ====