Car Signal Processor Buying Guide: Powered by ConsumerGuide and HowStuffWorks

Last Updated: 08/16/2007

The Basics: Car Signal Processors

Signal processors, or digital signal processors (DSPs), are the final stage in fine-tuning the sound in your automobile. The term covers a variety of components--by definition, digitally affecting the sound to alter it from the input signal. Signal processors can refer to an equalizer/crossover unit, a surround sound decoder, speaker steering (allowing you to turn on and/or off specific speakers) and delays for the speakers, sometimes referred to as digital time alignment.

An add-on equalizer might be just what you need to finally make your car audio system live up to its full potential. An equalizer lets you finely adjust the sound that gets fed to your speakers, allowing you to compensate for deficiencies in the frequency response of a speaker or an audible shortcoming in a component. Equalization also lets you attempt to control a car interior's typically troublesome acoustics. In very basic terms, equalization boosts or cuts certain ranges of frequencies from an audio signal--a very sophisticated tone control, with more than just bass and treble adjustments.

Stand-alone crossover units remain in the realm of high-end audio gear. While a few amplifiers do some sort of crossover-type frequency division, there are times when an audiophile wants and needs an external crossover unit. It's easy to see why--an external crossover unit usually offers the ability to fine-tune adjustments in a way no amplifier or head unit can.

How to Shop

Your reasons for purchasing a signal processor really determine what features you should look for. As most cars already have the amplification needed for four channels of speakers, some signal processors include amplification for the additional center channel and subwoofer that are required to reproduce 5.1 Dolby Digital and DTS surround sound. In addition to these set formats, some signal processors will add an artificial surround sound field to a regular stereo signal. These make the music sound like it's being played in a stadium, jazz club, or whatever the engineers decide to call their programs. These come as prenamed presets, however, you might want to take control and program your own personal sound fields and store them in user presets. Some processors have a wonderfully useful feature that compresses the audio signal. By reducing the overall dynamic range, the softer passages of music aren't lost under engine noise, and the loud peaks won't blow out your speakers.

A feature that is found on some higher-end processors is an independent equalizer for the left and right speakers. This feature helps to compensate for the sometimes non-ideal placement of speakers that are found in many vehicles. Digital time alignment also compensates for the placement of speakers, since you will rarely find yourself sitting in the perfect sweet spot evenly placed between all four speakers. This works more effectively than just using volume to control the balance of the speakers. Time alignment uses digital delays; psychoacoustics to fool the ear into thinking the speakers are centered on the drivers seat.

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.

Band-Pass Filters

High- or low-pass filters remove the frequencies above or below the range selected by the filter, changing the frequency response through this form of equalization.

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.

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.

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 30 Hz 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.

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.

Preamp Output

Generally, an RCA jack that sends the signal to an external amplifier--before the signal is amplified internally.

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, while 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.

Car Signal Processor Buying Guide

The Basics: Car Signal Processors

How to Shop

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