With the popularity of using digital media storage formats to store our favourite music, it is logical that we would want to deliver this music through our car audio systems. Whether your music is stored on an MP3 player, CD discs, or media storage cards.

There are several ways this can be achieved.

Play MP3, WMA, or AAC-encoded CD directly on a compatible stereo or changer
Connect a portable music player to your car stereo using an adapter.
Use an SD Card or a Memory Stick to transfer files onto a compatible car stereo
Store music directly on hard drive or flash memory, in compatible units.

Playing CD's Directly

Playing CD's is pretty straight forward. It is just a matter of loading the CD into the player or cassette changer and away you go. You will need to make sure that the music file format is compatible with the CD player.

Connecting the Portable Player To the Car Audio System

Once you decide what car audio system you will connect your portable player to, you need to decide exactly how to connect the two systems. This can be done by either:

Wireless FM transmitter and hard-wired FM modulator
Cassette Adapter
Bluetooth® transmitter
Auxiliary input

Using FM adapters

FM radio is restricted by FCC regulation to a frequency response [FR] of 30-15k Hz. This is about the same as a typical cassette player. The SNR of the FM tuner is also similar to a good tape player, around 70 dB. Therefore, if you feed your portable CD player or MP3 player music through an FM adapter to your radio the sound quality will be no better than the radio. The radio treats the music feed as if it is just another radio station.

There is one more selection to make if planning to pipe the music through an FM radio receiver; the type of FM adapter to use. You can use either :

A wired FM modulator - connected to your radio via the FM antenna connection. This requires removing the stereo to get to the antenna connector at the rear, but it's much less prone to outside interference than wireless transmitters.

Wireless FM transmitter - this broadcasts your music over the air to the stereo's FM tuner, just like normal incoming radio signals. Wireless is a much easier option to set up but the wireless transmission must compete directly with all the other radio signals and FM interference.

From a sound quality perspecitve, a wired transmitter is the best option.

Cassette Adapter

This is a simple adapter system, where an adapter in the form of a dummy cassette is used to connect the portable music player to the tape cassette system. The sound quality is similar to that one would expect from a tape deck. Whilst not suffering from any interference like the FM option, the sound quality is still not a good as a CD-player. Cassette adapter kits are an inexpensive and easy option; but wires running from mp3 player to tape deck is not pretty.

Bluetooth® Transmission

Bluetooth is a wireless digital transmission that uses rapidly changing frequencies rotation to overcome problems with interference and security. This is a good option for transmitting music from a portable player to an in-car audio system, especially if both the transmission system and the receiver component are both bluetooth enabled. If not, a Bluetooth adapter can be used, however, this add unecessary clutter to the set up.

Since Bluetooth signals are digital transmissions, they are capable of carrying more information, giving better sound quality, than FM transmissions [normally analog signals].

Bluetooth transmissions are full-bandwidth; with a frequency response of 20-20k Hz. The signal-to-noise ratio will vary depending upon the source player. The Bluetooth transmission will have little or no impact on the sound quality.

Auxiliary Input Jacks

Although using auxiliary input jacks requires the use of cables, the direct connection provides full-bandwidth [20-20k Hz] frequency response, giving a very clean signal. An auxiliary input, like Bluetooth, does not have a signal-to-noise ratio of its own. The SNR depends on the signal's source; the audio player.

Comparing Audio Connection Methods

The difference in sound quality between the various methods largely depends upon how the audio signal is manipulated:

Digital-to-analog conversion
FM conversion or transmission

With each conversion process, degradation of sound quality occurs. Whilst in some cases the loss in minimal and probably inaudible, the loss does accrue with each manipulation and can result in a minor loss of sound quality. Always use a patch cable to connect to any rear-mounted auxiliary inputs.

SNR and FR Comparison

For comparison purposes, here are the FR and SNR numbers for each option.

	Type	SNR	FR
BEST	Auxiliary Input	Same As Source	20Hz - 20,000Hz
BEST	Bluetooth Adaptor	Same As Source	20Hz - 20,000Hz
GOOD	FM Adaptor	70 dB	30Hz - 15,000Hz
	Cassette Adaptor	50 - 70 dB	30Hz - 18,000Hz

The Top 3

A direct connection via auxiliary input
Bluetooth adapters
FM adapters - open to outside interference.

Cassette adapters, especially if you are using a factory stereo. Aftermarket cassette stereos offer better cassette performance because of they tend to be on the upper end of that 50-70 dB signal-to-noise ratio.

Ease of hook up and elegance of the connection. The importance of the quality of the sound is often dictated by the sound environment of the vehicle. In a super quiet luxury car, small differences matter; but in a supped up big pipe street car; the noise interference will not be noticed.