Question I am not computer literate and I am not CD literate. Can you explain to me in easy-to-understand language what "MP3" means? And what exactly is an "MP3 Player"? Thank you very much.
Answer Hi Al
The MP3 movement is one of the most amazing phenomena that the music industry has ever seen. Unlike other movements -- for example, the introduction of the cassette tape or the CD -- the MP3 movement started not with the industry itself but with a huge audience of music lovers on the Internet. The MP3 format for digital music has had, and will continue to have, a huge impact on how people collect, listen to and distribute music.
If you have ever wondered how MP3 files work, or if you have heard about MP3 files and wondered how to use them yourself, then this article is for you! In this article, you will learn about the MP3 file format and how you can start downloading, listening to and saving MP3 files onto CDs!
The MP3 Format
If you have read How CDs Work, then you know something about how CDs store music. A CD stores a song as digital information. The data on a CD uses an uncompressed, high-resolution format. Here's what happens when a CD is created:
Music is sampled 44,100 times per second. The samples are 2 bytes (16 bits) long.
Separate samples are taken for the left and right speakers in a stereo system.
So a CD stores a huge number of bits for each second of music:
44,100 samples/second * 16 bits/sample * 2 channels = 1,411,200 bits per second
Let's break that down: 1.4 million bits per second equals 176,000 bytes per second. If an average song is three minutes long, then the average song on a CD consumes about 32 million bytes of space. That's a lot of space for one song, and it's especially large when you consider that over a 56K modem, it would take close to two hours to download that one song.
The MP3 format is a compression system for music. The MP3 format helps reduce the number of bytes in a song without hurting the quality of the song's sound. The goal of the MP3 format is to compress a CD-quality song by a factor of 10 to 14 without noticably affecting the CD-quality sound. With MP3, a 32-megabyte (MB) song on a CD compresses down to about 3 MB. This lets you download a song in minutes rather than hours, and store hundreds of songs on your computer's hard disk without taking up that much space.
Is it possible to compress a song without hurting its quality? We use compression algorithms for images all the time. For example, a GIF file is a compressed image. So is a JPG file. We create Zip files to compress text. So we are familiar with compression algorithms for images and words and we know they work. To make a good compression algorithm for sound, a technique called perceptual noise shaping is used. It is "perceptual" partly because the MP3 format uses characteristics of the human ear to design the compression algorithm. For example:
There are certain sounds that the human ear cannot hear.
There are certain sounds that the human ear hears much better than others.
If there are two sounds playing simultaneously, we hear the louder one but cannot hear the softer one.
Using facts like these, certain parts of a song can be eliminated without significantly hurting the quality of the song for the listener. Compressing the rest of the song with well-known compression techniques shrinks the song considerably -- by a factor of 10 at least. (If you would like to learn more about the specific compression algorithms, see the links at the end this article.) When you are done creating an MP3 file, what you have is a "near CD quality" song. The MP3 version of the song does not sound exactly the same as the original CD song because some of it has been removed, but it's very close.
From this description, you can see that MP3 is nothing magical. It is simply a file format that compresses a song into a smaller size so it is easier to move around on the Internet and store.
The Name
MPEG is the acronym for Moving Picture Experts Group. This group has developed compression systems used for video data. For example, DVD movies, HDTV broadcasts and DSS satellite systems use MPEG compression to fit video and movie data into smaller spaces. The MPEG compression system includes a subsystem to compress sound, called MPEG audio Layer-3. We know it by its abbreviation, MP3.
Using the MP3 Format
Knowing about the MP3 format isn't half as interesting as using it. The MP3 movement -- consisting of the MP3 format and the Web's ability to advertise and distribute MP3 files -- has done several things for music:
It has made it easy for anyone to distribute music at nearly no cost (or for free).
It has made it easy for anyone to find music and access it instantly.
It has taught people a great deal about manipulating sound on a computer.
Technology has made it easier to download and play your favorite music.
That third one was accidental but important. A big part of the MP3 movement is the fact that it has brought an incredible array of powerful tools to desktop computers and given people a reason to learn how they work. Because of these tools, it is now extremely easy for you to:
Download an MP3 file from a Web site and play it
Rip a song from a music CD and play it directly or encode it as an MP3 file
Record a song yourself, convert it to an MP3 file and make it available to the world
Convert MP3 files into CD files and create your own audio CDs from MP3 files on the Web
Rip songs off of various music CDs and recombine them into your own custom CDs
Store hundreds of MP3 files on data CDs
Load MP3 files into tiny portable players and listen to them wherever you go
To do all of these amazing things, all you need is a computer with a sound card and speakers, an Internet connection, a CD-R drive to create CDs and an MP3 player. If you simply want to download MP3 files from the Web and listen to them, then all you need is a computer with a sound card and speakers and an Internet connection -- things you probably already have!
Let's look at many of the different things you can do with MP3 files and the software that makes it possible.
Downloading and Listening
If you would like to download and then listen to MP3 files on your computer, then you need:
A computer
A sound card and speakers for the computer (If your computer has speakers, it has a sound card.)
An Internet connection (If you are browsing the Web to read this article, then you have an Internet connection and it is working fine.)
An MP3 player (a software application you can download from the Web in 10 minutes)
If you have recently purchased a new computer, chances are it already has software that can play MP3 files installed on its hard disk. The easiest way to find out if you already have an MP3 player installed is to download an MP3 file and try to double-click on it. If it plays, you are set. If not, you need to download a player, which is very easy to do.
There are literally thousands of sites on the Web where you can download MP3 files. Here are three of the biggest:
MP3.com
Emusic.com
Listen.com
Go to one of these sites, find a song and download it to your hard disk (most MP3 sites let you either listen to the song as a streaming file or download it -- you want to download). Most songs range between 2 and 4 MB, so it will take 10 to 15 minutes unless you have a high-speed Internet connection. Once the song has finished downloading, try to double-click on the file and see what happens. If your computer plays it, then you are set.
If you find that you cannot play it, then you need to download an MP3 player. There are dozens of players available, and most of them are free or shareware (shareware is extremely inexpensive). One of the most popular is WinAmp, which you can download from www.winamp.com. For a complete list of all of the available players, check out this page from MP3.com. Once you download and install a player, double-click on the MP3 file that you downloaded and it will play.
You are now ready to begin collecting MP3 files and saving them on your computer. Many people have hundreds of songs they have collected, and they create jukebox-like playlists so that their computer can play them all day long!
Taking the Files With You
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 need. These players are like portable cassette players except that they are smaller.
These players plug into your computer's parallel or USB port to transfer the data, and a software application lets you transfer your MP3s into the player by simply dragging the files.
Creating Your Own
If you have a CD collection and would like to convert songs from your CDs into MP3 files, you can use ripper and encoder software to do just that. A ripper copies the song's file from the CD onto your hard disk. The encoder compresses the song into the MP3 format. By encoding songs, you can play them on your computer or take them with you on your MP3 player.
AudioCatalyst is a popular ripper/encoder that you can use to do the job. This page from MP3.com contains an extensive list of other rippers and encoders.
Writing MP3s to CDs
If you have a writable CD drive in your computer, there are two ways to save your MP3 files on a CD:
You can write the MP3 files themselves onto a data CD in order to save them and clear some space on your hard disk. You can then listen to the files on any computer.
You can convert (decode) your MP3 files into full-size CD tracks and then save them to an audio CD. This allows you to listen to your MP3 files on any CD player.
WinAmp has a plug-in that creates full-size WAV files from MP3 files, and some of the encoders will also decode. Once you have the full-size CD tracks, then the software that comes with your CD-R drive will let you create an audio CD easily.
Understanding the CD
As discussed in How Analog and Digital Recording Works, a CD can store up to 74 minutes of music, so the total amount of digital data that must be stored on a CD is:
44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes
To fit more than 783 megabytes (MB) onto a disc only 4.8 inches (12 cm) in diameter requires that the individual bytes be very small. By examining the physical construction of a CD, you can begin to understand just how small these bytes are.
A CD is a fairly simple piece of plastic, about four one-hundredths (4/100) of an inch (1.2 mm) thick. Most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We'll return to the bumps in a moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic. A cross section of a complete CD (not to scale) looks like this:
Cross-section of a CD
A CD has a single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the center means that the CD can be smaller than 4.8 inches (12 cm) if desired, and in fact there are now plastic baseball cards and business cards that you can put in a CD player. CD business cards hold about 2 MB of data before the size and shape of the card cuts off the spiral.
What the picture on the right does not even begin to impress upon you is how incredibly small the data track is -- it is approximately 0.5 microns wide, with 1.6 microns separating one track from the next. (A micron is a millionth of a meter.) And the elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns long and 125 nanometers high. (A nanometer is a billionth of a meter.) Looking through the polycarbonate layer at the bumps, they look something like this:
You will often read about "pits" on a CD instead of bumps. They appear as pits on the aluminum side, but on the side the laser reads from, they are bumps.
The incredibly small dimensions of the bumps make the spiral track on a CD extremely long. If you could lift the data track off a CD and stretch it out into a straight line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long!
To read something this small you need an incredibly precise disc-reading mechanism. Let's take a look at that.
CD Player
The CD player has the job of finding and reading the data stored as bumps on the CD. Considering how small the bumps are, the CD player is an exceptionally precise piece of equipment. The drive consists of three fundamental components:
A drive motor spins the disc. This drive motor is precisely controlled to rotate between 200 and 500 rpm depending on which track is being read.
A laser and a lens system focus in on and read the bumps.
A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. The tracking system has to be able to move the laser at micron resolutions.
Inside a CD player
Inside the CD player, there is a good bit of computer technology involved in forming the data into understandable data blocks and sending them either to the DAC (in the case of an audio CD) or to the computer (in the case of a CD-ROM drive).
The fundamental job of the CD player is to focus the laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.
The hardest part is keeping the laser beam centered on the data track. This centering is the job of the tracking system. The tracking system, as it plays the CD, has to continually move the laser outward. As the laser moves outward from the center of the disc, the bumps move past the laser faster -- this happens because the linear, or tangential, speed of the bumps is equal to the radius times the speed at which the disc is revolving (rpm). Therefore, as the laser moves outward, the spindle motor must slow the speed of the CD. That way, the bumps travel past the laser at a constant speed, and the data comes off the disc at a constant rate.
Data Formats
If you have a CD-R drive, and want to produce your own audio CDs or CD-ROMs, one of the great things you've got going in your favor is the fact that software can handle all the details for you. You can say to your software, "Please store these songs on this CD," or "Please store these data files on this CD-ROM," and the software will do the rest. Because of this, you don't need to know anything about CD data formatting to create your own CDs. However, CD data formatting is complex and interesting, so let's go into it anyway.
To understand how data are stored on a CD, you need to understand all of the different conditions the designers of the data encoding methodology were trying to handle. Here is a fairly complete list:
Because the laser is tracking the spiral of data using the bumps, there cannot be extended gaps where there are no bumps in the data track. To solve this problem, data is encoded using EFM (eight-fourteen modulation). In EFM, 8-bit bytes are converted to 14 bits, and it is guaranteed by EFM that some of those bits will be 1s.
Because the laser wants to be able to move between songs, data needs to be encoded into the music telling the drive "where it is" on the disc. This problem is solved using what is known as subcode data. Subcode data can encode the absolute and relative position of the laser in the track, and can also encode such things as song titles.
Because the laser may misread a bump, there need to be error-correcting codes to handle single-bit errors. To solve this problem, extra data bits are added that allow the drive to detect single-bit errors and correct them.
Because a scratch or a speck on the CD might cause a whole packet of bytes to be misread (known as a burst error), the drive needs to be able to recover from such an event. This problem is solved by actually interleaving the data on the disc, so that it is stored non-sequentially around one of the disc's circuits. The drive actually reads data one revolution at a time, and un-interleaves the data in order to play it.
If a few bytes are misread in music, the worst thing that can happen is a little fuzz during playback. When data is stored on a CD, however, any data error is catastrophic. Therefore, additional error correction codes are used when storing data on a CD-ROM.
There are several different formats used to store data on a CD, some widely used and some long-forgotten. The two most common are CD-DA (audio) and CD-ROM (computer data). If you would like more information on either of these formats
How can I burn MP3s from my computer onto CD-Rs?
MP3 music files are great when you are sitting at your computer. If you have one of the portable MP3 players, it is also easy to carry MP3s with you and listen to them through headphones. But if you want to play MP3 files in your car and your car has a CD player in it, or if you want to play them on your home stereo, then what you need to do is move your MP3 files onto a CD.
To create a CD from MP3 files, you need to do three things:
You need to download the MP3 files you want to listen to onto your computer. You can get MP3 files from places like mp3.com.
As described in How MP3 Files Work, an MP3 file is a compressed version of a CD track. You therefore need to expand the MP3 file back into a full-size CD track. This process is known as decoding, and you need to have decoding software on your computer to do it. You can purchase a decoding package or download free or trial software from the Internet.
You then collect all of the CD tracks together in a directory and write them to a writable CD. Your CD-R drive normally comes with software for doing this. When you write out the audio tracks, you have to be sure to tell the software that you wish to create an audio CD rather than a CD-ROM.
Since MP3 files can be easily downloaded from the Internet and your CD-R drive comes with software for writing audio tracks to a writeable CD, the main thing you need is the decoder. Three good places to look for a decoder include:
Winamp ww.winamp.com/
MP3 Software
MP3 Software
Download your songs, decode them and write them to a CD. Then you can pop the CD into any CD player and listen to your songs anywhere!
