A-weighting
A standard compensation (weighting) curve sometimes applied to audio measurements to account for the ear's response to low-level sound. Frequently applied to measurements of the residual noise levels of wireless microphone systems and other electronic devices. ("A-weighted noise.")

Absolute Attenuation
Defined as dBa, this term describes the absolute attenuation at a given frequency.

Absorption
The conversion of sound or radio frequency (RF) energy into heat.

Absorption Loss
For wireless microphones, the loss that occurs when a transmitted signal passes through a material that absorbs a portion of the RF energy, reducing the signal level available to the receiver.

Acoustic Phase Interference
See Phase Cancellation.

Active Antenna
An antenna with an integrated or attached RF preamplifier or RF line amplifier. There is no practical difference between an active antenna and an antenna connected to a separate RF preamplifier.

Active Circuit
An electronic circuit which uses active devices such as transistors or integrated circuits for its operation and which requires a power source for operation.

Active Device
Devices such as transistors, integrated circuits and vacuum tubes that require an external power source in order to perform an intended purpose, such as amplification.

Active Splitter
An electronic device that consists of an RF signal splitter (power divider) preceded by an RF amplifier that compensates for the RF loss of the splitter. Used to allow one antenna to feed several receivers.

Adapter Mount
Term used to describe gooseneck microphones with a 5/8"-27 threaded rotating collar which screws onto the 5/8"-27 threads of a mic stand, mounting stud, etc.

Adjacent Channel Rejection
The ability of a radio receiver to reject interference from an undesired signal on another nearby channel frequency. In wireless, unless the frequency separation between the desired signal and the adjacent signal is specified, the term is generally not of any practical significance.

Alkaline Battery
A type of battery often used in electronic equipment. Offers longer operating life than other types of readily-available batteries.

Amplitude Flatness
Defined in dB, this term means the total amplitude variation across a given frequency passband. This value includes roll-off associated with finite unloaded Q.

Amplitude Ripple
Defined in dB, this value refers only to the signal variation caused by the VSWR and does not include the roll-off associated with finite unloaded Q.

Anechoic Chamber
An acoustic space without echo or reverberation. Often used for the acoustic testing of microphones and loudspeakers.

Antenna
A conductive physical device designed to radiate RF energy from a transmitter, or to capture RF energy for application to a receiver.

Antenna Directivity
The property of certain types of antennas that receive or transmit a greater signal in one direction as compared to other directions. Such antennas will have greater than unity (0 dB) gain in the preferred direction or directions and less than unity gain in other directions.

Antenna Diversity
A form of diversity that uses three receiving antennas. Each antenna is isolated by an RF amplifier, then the three signals are combined into a single composite output signal which is applied to a non-diversity receiver. No longer used by any major manufacturer due to unpredictable and generally poor performance. This name is sometimes erroneously used for phasing diversity systems.

Antenna Efficiency
The actual amount of RF energy received or transmitted by an antenna as compared to an ideal antenna. An antenna's efficiency can be reduced by it having incorrect dimensions for the frequency of operation, improper mounting, electrical losses and by other factors.

Antenna Gain
The ratio of the signal, usually expressed in dB, received or transmitted by a given antenna as compared to an isotropic or dipole antenna. Antenna gain can only be achieved by making an antenna directional, that is, with better performance in one direction than in others.

Antenna Splitter
An electronic device that consists of an RF signal splitter (power divider) preceded by an RF amplifier that compensates for the RF loss of the splitter. Used to allow one antenna to feed several receivers.

Attenuate
To reduce the amount of energy contained in an electrical or radio frequency signal. Also, to reduce the intensity or level of sound waves.