Information of Head Unit
An automotive headunit has the following elements:
Many car audio systems have volume controls on the steering wheel that can change radio stations or CD tracks and switch audio sources. Of course, a head unit also controls the overall volume of the system. But today you may not even have to touch a knob or button on the dash to operate certain aspects of a car’s audio system.
Some cars also have steering-wheel switches that allow the driver to operate an audio system via voice commands. And some even let the driver switch audio sources or change radio stations and CD tracks just by pushing a button and saying a command.
Higher-end systems also use sophisticated digital signal processing (DSP) technology to further shape the sound and combat the ambient noise that’s common in a car’s cabin from engine, road and wind noise. In addition to operating every audio source, the head unit can also tailor the sound with tone controls for bass and treble or with a built-in equalizer.
*Disc-Based Music Sources
A compact disc player is the main non-radio audio source in cars today. Head units that play both CDs and DVDs are also popular, since they let consumers play DVD videos on separate screens in the back – and in the front, provided the car is parked. Some head units can control remotely mounted CD changers. Some head units also have a built-in hard-disk drive that can store music files transferred from a CD or DVD. These disk drives range in size from 10GB to 30GB, with larger sizes allowing more music storage.
Most head units that play DVDs can also play MP3 files burned onto those discs. DVDs can hold significantly more files than a CD. Car head units also play recorded material from various sources. Many modern CD players can also play MP3 music files that have been burned onto a disc, which makes many more songs available.
The amplifier is actually made of two components, a power amplifier and a preamplifier (preamp). most automotive head units have a small built-in amplifier. The power amplifier further strengthens that signal so it’s powerful enough to move the voice coils of the speakers in the system. The preamp takes data from a radio tuner, CD player or other audio source and slightly boosts it before sending it to the power amplifier.
In the early days of automotive electronics, the only entertainment option was to tune in an AM radio signal – hence the name “tuner.” Next came FM radio. In metropolitan areas, radio stations now might also broadcast HD Radio.
More automakers are adding HD Radio capability to their vehicles as standard equipment or as an option, even though consumers are still largely unaware of HD, despite the improved sound quality and extra features. An HD signal is a high-quality digital simulcast of standard analog AM or FM programming. You’ll want to check HD Radio availability in your area before paying extra for the feature.
Some stations also broadcast completely separate programming on sub-frequencies that are only available with an HD tuner. Of course, your car’s head unit must have a dedicated HD Radio tuner to receive these broadcasts.
The antenna is a critical part of the radio tuner. Many automakers have recently adopted a “shark fin” style of antenna for better aerodynamics and a more streamlined look. For years, the antenna was a metal mast mounted on the exterior body of the car. If you don’t see either type of antenna on your vehicle, it probably has an array of thin wires embedded in the windshield or back glass that serves as a radio antenna.
Aftermarket satellite radio and HD Radio tuners can also be added to head units that do not have them built in. Stations don’t fade the way AM and FM does as you drive away from an area, and the sound of satellite radio is higher quality than that of analog radio. Satellite radio from Sirius and XM is more popular with consumers. These subscription-based services offer hundreds of channels of programming.
*Portable Music Sources
Most modern head units offer some way to integrate portable music players like the iPod into a car’s audio system and control them through the head unit. The most basic connector is the “aux-in jack.” You plug an inexpensive accessory cable into the aux-in jack, which in turn connects to the headphone jack of an iPod or other music player. You operate the device using its own controls with an aux-in jack, although a car’s head unit will adjust the volume. An aux-in jack also won’t charge a music player’s battery.
A technology called Bluetooth audio can wirelessly send music files from a compatible device to the car’s audio system, just as Bluetooth for hands-free phoning allows you to hear a caller’s voice over the sound system’s speakers. There’s a caveat with Bluetooth: The controls are limited to basic functions such as play/pause and track-skip forward/back, and the head unit usually doesn’t show information such as an artist or track name.
An even better way to connect a portable music player is via a USB port. In most cases, you can operate the device using the head unit’s controls. The battery will also be charged when it’s connected via USB. Most cars with USB ports will play music files directly from a USB thumb-type memory drive as well. A few vehicles also have a SD card slot for access to music files on that portable media source, which is most often associated with digital cameras.