Glossary of Audio Terms

The basic unit of capacitance. For instance, a capacitor has a value of one farad when it can store one coulomb with one volt across it.

Federal Communications Commission. US agency responsible for governing radio interference matters.

When the sound from a loudspeaker is picked up by the microphone feeding it, and re-amplified by the same loudspeaker, only to return to the same microphone, and so on, forming a perpetual acoustic loop. After each cycle, the signal grows larger until the system "feeds back" onto itself creating the "scream" or "squeal". Sometimes called

An unintentional leakage of audio from a loudspeaker, which gets picked up by the microphone which is being used for originally capturing the audio. If too much feedback occurs, the system can go into self-oscillation, causing unpleasant howling or squealing.

An audio signal processing device that utilizes an automatic detection system to determine acoustic feedback frequencies and then positions filters to cancel the offending frequencies.

An audio process where two of the same signals are played together, but one variably delayed against another.

The true reproduction of an audio signal. The variation in the output level of a flat response should be less than 1 dB above or below a median level over the audio spectrum.

The band of frequencies that pass through a device with a loss of less than 3 dB, expressed in Hertz. For an amplifier, this is usually measured at a low power level (1 watt into 8 ohms, for example). This is not the same as Power Bandwidth, which is measured at full power.

Expressed in Hz. Typically the frequencies at which the output of a loudspeaker drops

How level or accurate the gain of an audio device is over a range of frequencies.Expressed in Hz. Typically the frequencies at which the output of a device drops 6 dB below the device's nominal output or the point at which the frequency response of a device falls outside of a +/- 3 dB window.

Federal Trade Commission. US agency responsible for enforcing federal antitrust and consumer protection laws. FTC guidelines state that power ratings must be met, with both channels driven, over the stated frequency range (usually 20 Hz to 20 kHz), at no more than the rated THD. The THD rating is supposed to be valid down to 0.25 watt over the entire frequency range. The FTC Amplifier Rule, first implemented in 1974, states 60 minutes at 1/8 of full power (with a 1 kHz sine wave). Prior to 2000, the required 60-minute preconditioning was at 1/3 of full rated power. This makes 2-ohm FTC ratings extremely rare among all amp manufacturers, since 2-ohm operation is right on the edge of where current-limiting protection circuits will kick in. Fortunately, music waveforms are less demanding than constant-level sine waves or pink noise, and amplifiers designed for low impedances handle normal program material into 2 ohms with no problem. The test loads are non-inductive precision load resistors.