A/B Comparison A back-and-forth listening comparison while auditioning two musical sources or presentations.

AC-3 (audio coding 3) - Dolby's digital audio data compression algorithm adopted for HDTV transmission and used in DVDs and CDs for 5.1 multichannel use. Competes with DTS audio.

ACDrive (Advanced Codec Drive) - A media management system used by Kenwood on select headunits

Acoustic Suspension - a sealed or closed box speaker enclosure. For details and more enclosure types see Woofer Enclosure Designs.

Acoustical Energy - Energy generated by fluctuating waves of pressure called sound waves .

Active Circuit - A circuit that requires current to perform it's designed task For example, the adjustable Crossover on an amp is active verses the inactive crossover used on a 2-way speaker.

Alternator Whine - A whining noise in the amplifier's output that appears as the rotational speed of an engine increases. The noise is usually the result of a voltage differential created by more than one ground path or a poor ground path to the affected equipment.

Ampere (Amp) - A unit of measurement that defines the rate of flow of electricity (Current) in a circuit.

Amplification Classes - All sound is a sinusoidal waveform. It has alternating peaks and valleys. The center point of each wave is the zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave. When a amplifier operates in Class A , the output tubes or transistors amplify the entire waveform without splitting it into positive and negative halves. In Class AB, used in the majority of amplifier designs, the signal is split into two halves, positive and negative, and each half is sent to a tube or transistor circuit for amplification. Both sides work in tandem, and the two halves are recombined at the output section to reconstruct the whole signal. This technique increases the amount of power that can be applied, but increases distortion. Class D operation is essentially a rapidly switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Theoretically, since the output devices are either completely on or completely off they do not dissipate any power, greatly increasing efficiency. Not musically the best sounding design, but popular for subwoofer use where maximum power is necessary, and slightly elevated levels of distortion are easily tolerated.

Amplitude - The maximum value of a waveform (or any constantly varying quantity).

Amplitude Modulation (AM) - A method of modulation in radio broadcasting. The amplitude of the carrier voltage is varied in proportion to the changing frequency value of an applied (audio) voltage. (Also see Frequency Modulation).

Analog - An electrical signal in which the level and frequency vary continuously in direct relationship to the original acoustical sound waves.

Analog to Digital Converter (ADC) - A circuit that converts an analog signal into a digital signal. With a continuous input signal the ADC will check the signal several time per second (sampling), assign values to the samples and represent it as a binary value for use in a digital signal (quantization and encoding).

Anechoic Chamber - A special room that is constructed without acoustically reflective surfaces, such that it is without echoes, or an-echo-ic. This experimental setup enables engineers to more precisely measure the acoustical properties of many types of equipment.

Aperiodic Enclosure - Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but to yield a smoother response pattern by lowering the Q of the system and reducing the impedance peak at resonance. The resistive vent damps the driver in much like stuffing a sealed enclosure allowing the design to be 20% (or more) smaller due to the extra damping of the resistive vent.

Attenuator - A device to decrease or increase the strength of a signal.

Audio Frequency Spectrum - The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

Audiophile - A species of dedicated audio fanatics who actually read definitions like this.

Auto Memory - A tuner feature that automatically finds the strongest stations in the local area, and places them in preset station memories.

AWG - Acronym for American Wire Gauge, a standard for measuring the diameter of wire commonly used in electrical circuits. The higher the AWG number, the smaller the thickness of the conductor