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Antishock Memory
A feature of DVD, CD and MiniDisc players that stores audio data in a memory buffer that is output if the main signal mistakes.
Antitheft Protection
A variety of ways a system attempts to prevent theft, including a detachable faceplate, a masking face plate, or systems that will not operate if disconnected from the battery without a custom code.
Changers
A CD, MiniDisc, DVD or MP3 unit that handles more than one disc--a multiple player.
Digital/Analog Tuner
An analog tuner uses conventional circuitry with a tuning knob or thumbwheel and pointer to show you the frequency to which you are tuned. A digital tuner, more accurately a synthesized tuner, permits using a digital frequency read-out and presetting radio stations for touch tuning.
Direct Access
Using a numeric keypad, you simply press the corresponding key to hear a specific track.
Distortion
This is a measurement of the deviation from the original signal to the reproduced signal. Distortion is a harsh sounding artifact that alters, in a negative way, the signal.
Dolby Digital
Formerly AC-3, Dolby Digital is a method developed by Dolby Laboratories to digitally encode up to 5.1 discrete channels of high-fidelity sound in a single digital bitstream. The .1 channel refers to the "low frequency effects" (LFE) channel that carries only low frequency information, which is usually directed to the subwoofer upon playback. The encoded signal can be any number of channels, from a mono signal to the maximum of 5.1 (front right, center, front left, surround right, surround left, subwoofer) although it has now become common to use Dolby Digital to refer to any 5.1 signal.
Driver
The element of a speaker that actually produces the sound.
DTS
Stands for Digital Theater Sound and comes from the company of the same name. DTS accomplishes much the same thing as Dolby Digital, but it does so slightly differently. The two systems are incompatible when it comes to decoding, but after the signal is decoded, it is otherwise the same to the receiver, allowing many new receivers to incorporate both. Thus far, DTS has not made much impact on the home market, and minimal software is available that uses the system. The system was originally engineered for movie theaters.
Dynamic Range
The difference between the loudest peak and softest passage. It can also refer to the spectrum between the edge of distortion at the high end of a product's performance and the product's noise floor.
Equalizer
A circuit or program that changes the frequency response of a signal, boosting or cutting selected ranges from the overall response.
FM Modulation
For someone unwilling to remove their factory installed equipment, an FM modulator takes the audio output of an FM-modulated add-on and generates a radio frequency (RF) signal that is received by your car's FM radio tuner.
Frequency Response
Also listed as Frequency range, is the spectrum of frequencies produced by a product, within a certain tolerance. For example, a frequency response of 30Hz to 18kHz (+/- 3dB) means a product produces all frequencies from 30Hz to 18kHz without dropping or peaking three decibels. The signal below and above that range does drop off more than 3dB, so the range is really the usable spectrum of sound.
Head Unit
The usable part of a component that is mounted in the dashboard is commonly referred to as a head unit. It controls the components, either internally or remotely installed, such as a changer mounted in the glove compartment or trunk.
Impedance
Impedance is commonly listed from 4 to 8 ohms, with some ranging from 2 to 16 ohms. This is a technical description of the amount of inductive resistance a speaker offers to the flow of electrical signals from a receiver. Under normal circumstances, impedance bears no relation to sound quality, but many receivers need a minimum of 4 ohms to work properly. A good receiver may work with 2 ohms, but other receivers or amplifiers will automatically shut off or blow a fuse. If you intend to use two pairs of speakers in parallel from the same terminals, choose loudspeakers rated at least 8 ohms. Also note that speaker impedance ratings are nominal, meaning that a speaker may actually fall below its rated impedance at some frequencies.
OEM (original equipment manufacturer)
This refers to the factory-installed system that comes with a car. Many car manufacturers are using name brand products, either standard or part of an upgrade package.
Player
Where as a changer plays many discs, a player can hold and play only one at a time.
Programmable
Customizing the playback order of tracks on a CD, MiniDisc, MP3 player or even a cassette by storing your own play list, or using a random function that scrambles the order, or selecting one track to repeat.
Signal-to-noise ratio
The ratio between the audio signal and noise floor. A low number indicates that the noise and music are closer together--the higher the number, the less noise is apparent.
Surround Sound
This covers many different formats that play sound through multiple speakers to simulate the natural sounds from many locations.
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