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Investigating the Audio Head Unit

clarion stereo

Say the term car stereo and most people think of the thing in your dash with knobs and lights that you stick a disc into. But the in-dash part of a car audio system is only a small, part of the whole. Also known as a car radio the head unit is the most visible part of a system and one of the only components you regularly interact with.

The head unit is also the only part of a system that generates an audio signal and it's a conduit for various media options. Only a few years ago, you had just a few choices when it came to media: AM and FM radio, CD, cassette, and maybe DVD. But in the last few years, there's been a huge proliferation of new mobile-media options that allows you to bring music and video into the car in myriad ways.

MP3 and other digital music file formats forever changed how people store music, whereas the iPod phenomenon revolutionized the way people access and carry it. Now you can burn hundreds of files onto a CD or carry your entire music collection on a portable media player (PMP) like the iPod. And you can also store dozens of digital music files on SD cards or a USB drive, and even on your mobile phone. That doesn't even include the latest over-the-air music options, such as satellite and HD radio.

Choosing CD or DVD

The majority of car audio head units currently available are either AM/FM/CD or AM/FM/DVD receivers, with CD-based heads outnumbering DVD-based heads by a considerable margin. Which you choose will largely depend on your music collection as well as your budget because DVD receivers are a bit more expensive. But you should also look beyond the disc and consider the other media options a head unit will provide.

If you mostly listen to CDs, a CD receiver is the obvious choice. But because even budget-priced CD receivers now come with the option to add external sources, such as an iPod, satellite radio, or USB drive, you don't necessarily have to be restricted to CD-based entertainment. And with CD becoming somewhat of a dinosaur format, even if you do buy a CD receiver, you'll want to give yourself other media options. If you anticipate that your system will be part of a larger car audio/video system, a DVD receiver is the obvious choice.

After DVD was introduced in 1997, it quickly became the most successful consumer electronics product ever, as people abandoned their clunky old VCRs for DVD players and the more robust but familiar-looking DVD. The format also kick-started the mobile video boom of the last few years because it finally created a convenient way to bring video into a vehicle.

Before PMPs like the iPod took off, it looked like DVD would dominate the audio/video world, and this has pretty much been the case in home entertainment, where CD players are about as popular as VCRs. But CD has hung on as a significant if slowly dying force in the car audio world, mainly because CD-based heads are cheaper than DVD head units. But if you can afford to go with DVD instead of CD, the extra features and flexibility are worth it.

How the iPod Changed Everything

When DVD first started to take off in the late 1990s, I spoke with an engineer in the recording industry who predicted that DVD would be the last disc-based music format for consumers. This was in the early days of MP3 and a couple of years before the iPod was introduced in 2001. No one could have predicted how Apple's iPod would change the way people store, listen to, and carry music. Although MP3-based PMPs had already been around for a few years, with its elegant yet simple design, intuitive interface, and Apple's straightforward iTunes software, the iPod became a phenomenally popular product the likes of which the consumer electronics industry has never seen.

Although CD is still the most widely available format among car audio head units, its days are undoubtedly numbered. CD sales are in a steep decline as people are abandoning the disc in droves for music formats that are more convenient and less costly.

Disc-less digital music files are undoubtedly the wave of the future and CDs and DVDs will one day be regarded with the same sort of nostalgia that the vinyl LP is viewed today.

Music Files Go Mobile

MP3 is the computer music-file format that let the digital genie out of the bottle by essentially freeing digital music from the disc. Instead of record companies deciding what music you could have on a CD, now people who already owned the music on CD could rip MP3 files onto their computer's hard drive and then burn them in any combination they chose onto recordable CDs. This also allowed storing hundred of songs on a single recordable CD. It took the concept of the mix tape into the digital age.

Space Versus Sound

The downside to MP3 is that there's an inherent trade-off between file size and sound quality. When creating an MP3 file, the user can typically select a bit rate that specifies how many kilobits the file may use per second of audio. The lower the bit rate, the smaller the file size. Conversely, the higher the bit rate, the higher the quality, but the larger the file size and the fewer songs you can fit on a hard disk or CD.

When converting a file to an MP3, bit rate can be varied from 32 to 320 kilobits. CD quality MP3s are typically converted at 128 kilobits per second, although more demanding music recordings can require encoding at 192 kilobits per second or higher. Most MP3 encoders, however, simply use one bit rate for an entire file to make the process easier and faster.

Doing Windows

In 1999, Microsoft introduced the WMA (Windows Media Audio) digital-file format to compete with MP3. WMA files are encoded in much the same way as MP3s, but Microsoft claims WMA has a higher sound quality than MP3 and other lossy file compression formats. Regardless, all you need to know is that WMA, along with MP3, is a file format supported by most car audio manufacturers. Also, keep in mind that many people use the term MP3 generically to describe all types of digital music format.

The reason you need to know all of this is that many CD and DVD receivers in both the aftermarket and in stock systems now supports MP3 and WMA playback. This means you can potentially burn hundreds of music files onto a CD or DVD and then take it into your car.

The Disc-less Drive

It would have been difficult to imagine a car audio head unit without a disc drive only a few years ago, but now it's looking like the future. Alpine and Clarion concurrently introduced the first disc-less head units at the Consumer Electronics Show in January 2007.

Alpine was the first car audio manufacturer to add iPod integration to an aftermarket head unit, so it's not surprising that the forward-thinking company was the first to offer a radio specifically designed to accommodate the iPod.

Clarion's FB275BT head unit was another disc-less model introduced at the 2007 Consumer Electronics Show. Instead, it has a slot for an SD card behind its fold-down faceplate. ID3 tag information such as artist and song title is displayed on the FB275BT's color display.

With the CD going the way of the cassette in the car, look for more manufacturers to introduce head units without a disc mechanism. This is not only of benefit to music lovers in the MP3 era, but it also means that in-dash head units will have fewer moving parts and are therefore potentially less likely to break.

From Car Audio for Dummies, copyright © 2008 by John Wiley & Sons, Inc., Hoboken, New Jersey. Used by arrangement with John Wiley & Sons, Inc.

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