A Guide for Online Information About:

PORTABLE MP3 PLAYERS

by Rick Prescott

The MP3 format has completely rewritten the rules of music distribution. It has had a huge impact on how people collect and listen to music. And with the growing popularity of MP3 players, it is moving beyond the computer.

What is MP3?
MP3, or MPEG3, stands for Moving Pictures Expert Group Layer III. The Moving Pictures Expert Group is the organization responsible for developing the format, and "Layer III" refers to the third revision of the compression format. The current version, MP3, has a compression ratio of 1:12 and a minimum bandwidth of 128 Kbps, meaning every 8 s of audio requires 128 Kb of storage space. Compressing an audio file to MP3 can trim the file size down to less than a tenth of the original file with minimal loss in quality. In English, the MP3 technology makes large audio files much smaller, therefore, making them easier to download, copy, and store. The MP3 encoder cheats a bit by removing the parts of the recording not audible to the human ear. Although MP3 isn't quite as clear and rich as CD sound, it's pretty close. MP3 files can be created from music on CDs (or any analog or digital recording from .WAV files to DAT) or downloaded from thousands of web sites on the Internet.

For more information on MP3 files and file sizes from HowStuffWorks, see:

ý How MP3 Files Work—details on the compression process
ý How Analog and Digital Recording Works—details on turning sound into bytes
ý How CDs Work

MP3 players are available in three types:

• Personal players: By far the most common type. Most players hold at least 60 min. of music; others can store twice that. These small portable units start around $200, with fully-featured models going for more than $300. Most run on AA batteries. Models with rechargeable batteries can play for 10 to 12 h before needing to be recharged. Some players include headphones and FM tuners.

• Home players: These models differ from the original MP3 portables, in that most are designed to play MP3 files burned onto CDs. This requires the necessary software for "ripping" digital files from CDs and other sources and converting them to the MP3 format, plus a CD-R drive to "burn" them onto a CD. High-end models can store as much as 300 h of digital audio. Basic models start at around $300 and the top-shelf variety are about $1000.

• Car players: Some, like home players, are designed to play MP3 files burned onto CD. A few have their own storage drives capable of holding close to 30 Gb of music with approximately 17 h of music per gigabyte. Most also include FM tuners. These models are removable from the dash for security and so that they may be linked to your PC for file transfer. Prices run from about $300 for the type that play CDs to $1200 or more for the type that includes its own storage drive.

 

The remainder of this article will focus on portable personal players:

Many people who start collecting MP3 files find that they want to listen to them in all kinds of places. Small, portable MP3 players answer this demand. These players are like portable cassette or CD players, except they are smaller and use solid state memory instead of a physical medium like a tape or CD. All of the players currently on the market include a software application that lets you transfer your MP3 files into the player. Most of them also include utilities for copying music from CDs or web sites and the ability to create custom playlists.

The MP3 player is a wonderful example of a new use for existing technologies. None of the components in a typical MP3 player is radical, or even new, technology. By simply combining these components in a new way and writing some code to control it all, manufacturers have created an entirely new line of consumer products! The job of the MP3 player is pretty straightforward. When you play a song, the player must:

1. pull the song from memory byte by byte
2. decompress the MP3 encoding
3. run the decompressed bytes through a digital-to-analog converter
4. amplify the analog signal so you can hear it

The main difference between a portable CD player and an MP3 player is that the CD contains bytes instead of memory, and on a CD the bytes are already decompressed so no decompression is needed.

Parts of a Player
Let's take a look at the components that make up a typical MP3 player:

• data port
• memory
• microprocessor
• Digital Signal Processor (DSP)
• display
• playback controls
• audio port
• amplifier
• power supply

The player plugs into your computer's USB port or parallel port to transfer data. USB-based players transfer data several times faster than those that use a parallel port. The MP3 files are saved in the player's memory. Memory types include:

• internal flash memory
• CompactFlash cards
• SmartMedia cards
• Memory Stick
• internal microdrive
• Iomega Clik! removable media

With the exception of the last two, these are all types of solid state memory. The advantage to solid state memory is that there are no moving parts; and no moving parts means better reliability and no skips in the music.

The microprocessor is the brains of the player. It monitors user input through the playback controls, displays information about the current song on the LCD panel, and sends directions to the DSP chip, telling it exactly how to process the audio.

The DSP pulls the song data from memory, applies any special effects (or EQ), and streams it to the amplifier. The DSP runs a decompression algorithm that undoes the compression of the MP3 file, and then a DAC turns the bytes back into waves.

The amplifier boosts the strength of the signal and sends it to the audio port, where a pair of headphones or ear buds are connected.

All of the portable MP3 players are battery-powered. Most use one or two AA batteries and last for approximately 10 to 12 h on a single charge. Many of the players also have AC adapters so they can be plugged into a normal electrical outlet, and some even offer DC adapters for use in a car.

The latest innovation is MP3 players that contain tiny hard disk drives. These drives can store 10 to 100 times more than flash memory devices can! Portable MP3 players come in a wide assortment of colors and flavors.

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