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Music Technology
Digital Music: iPods, Movable Music &
Tunes In Your Pocket
The next time you download your favorite tune from the Internet, rock out on music while riding home on the bus or just listen to a cool iPod "podcast," take a moment and thank the person responsible for all this happening technology.

It all started back in 1877 with Thomas Edison. When he invented the phonograph, he also accidentally invented the music industry. Edison is better known for creating the light bulb, but he also created a type of crude tin-foil cylinder phonograph. Edison didn't have visions of R&B hunk Usher or Tex-Mex Trio Los Lonely Boys busting out on the top-40 Hit List. In fact, the last thing on the inventor's mind was using his new device to record music. Edison, as a businessman, thought there was a better market in dictation equipment that could record contracts and business letters. "Recordings don't lie," he said.

The brilliant Edison totally resisted music as the "Killer Application" (computer speak for "must have") for the new technology, until competitors proved there was a market for it.

In Edison's day, there was no record industry or recorded music. Home entertainment technology hardware consisted of a piano, and usually a teen-age daughter to play it. The software equivalent was a piece of sheet music. People generally gathered together for back-porch hoe-downs or jam sessions around a sitting-parlor piano. There was hardly an air-guitar in sight.

Inventing the phonograph was a bit of luck mixed in with Edison's keen observation. While working to improve the efficiency of a telegraph transmitter, he noted the paper tape from the machine gave off a noise resembling spoken words when played at a high speed. Edison wondered if he could record a telephone message. He began experimenting with the diaphragm of a telephone receiver by attaching a needle to it. He reasoned that the needle could prick paper tape to record a message. His experiments led him to try a stylus on a tinfoil cylinder, which, to his great surprise, played back the short message he recorded, "Mary had a little lamb." The machine had two needles—one for recording and one for playback. When words were spoken into the mouthpiece, the sound vibrations would be indented onto the cylinder by the recording needle. When the cylinder was spun on a spring-wound device, a stylus translated the various indentations back into a human voice. This cylinder phonograph was the first machine that could record and reproduce sound.

The music world would never be the same with the advent of the phonograph and later the gramophone, by the Victor Company, which played 12-inch diameter disks on a wind-up Victrola. (Victrola is the brand name for a line of internal horn phonographs made by the Victor Talking Machine of Camden, NJ from 1906 through 1929.) More so than what MTV did for putting music on TV, this was a true music revolution with a century of long-lasting effects. Nobody who made or listened to music could ignore the phonograph. Songwriters shortened their compositions so they'd fit on one side of a 78 rpm record. Singers worked on their projection and enunciation so that the primitive recording technology would better render their voices. And just like today, fans were able to enjoy more kinds of music than many had ever known even existed.

Instead of the back porch or the church vestibule, music lovers spent more time gathered around the horns of their Victrolas, leaning with their ears cocked like the company spokesdog, Nipper.

Question 1: How Do You Make A Record
Album Without Vinyl?
 In the early 1900s, there wasn't any plastic or vinyl that could be pressed into records. Edison's scientists, playing a game of industry catch-up, improvised and molded phenol and formaldehyde mixed with wood-flour and a solvent into a heat-resistant disc. This material always remained absolutely flat, which was essential as it formed the core of the disc record. A resin varnish called Condensite—sort of like the resins or coatings we use when refinishing old furniture—was applied to the core, and then the disc was stamped in the record press as a master. The finished 10" disc weighed ten ounces, about five times heavier than Apple's iPod. Edison claimed that his records could be played 1,000 times without wear. Oddly, Edison's claim sounds nearly like the claims of "indestructibility" that surrounded the release of Compact Discs in the 1980s. Unlike CDs, Edison's disks were just too expensive and never really caught on with the masses.

Music: Mankind's Universal Language
The Jimi Hendrix Experience Music is considered the universal language, the salve to calm the savage beast, the device which separates mankind from the lower forms on the gene pool. In actuality, scientists think the first music and musical instruments were probably the result of stone-age toolmakers clanking away in their caves looking for some distinctly expressive sound. The classic acoustic instruments, such as the strings, horns, woodwinds, and percussion of the modern orchestra have been around for centuries. For hundreds of years, the detailed construction of prized acoustic instruments, especially in the string family, has remained a mysterious art. Not so for electronic instruments or recorded music. Guitars were first connected to electronic pickups back in the 1930s and it took until the 1960s, when Jimi Hendrix and others turned up the volume and started exploring the virtues of distortion and feedback. The electric guitar became part of a complex acoustical-electronic system.

"Music is a moral law. It gives soul to the universe, wings to the mind, flight to the imagination, a charm to sadness, gaiety and life to everything. It is the essence of order and lends to all that is good and just and beautiful."-- Plato

In the early 1970s, the rage was voltage-controlled analog synthesizers, such as the MiniMoog, which produced spacey, other-wordly tunes, something like a cross between a piano and a woman's scream. The Moog Drum Controller introduced in 1973, employed a special sensor in the drumhead and gave audiences their first exposure to synthesized drums in the concerts of old dinosaur rock bands such as Emerson, Lake and Palmer. The early 1980s saw the development of the Musical Instrument Digital Interface—a standard protocol for the interchange of musical information between musical instruments, synthesizers and computers. It defines the codes for a musical event, which includes the start of a note, its pitch, length, volume and musical attributes. Instead of recording the sound waves as in a tape recorder, the computer stores the music as bits of digital data and computer codes on the hard disk. The recording can be edited in an entirely different manner than with conventional equipment. MIDI files also take up much less disk space than sound files that contain the actual digitized music. MIDI makes an ideal system for storing music on digital media due to its small storage requirement compared with digitizing actual music.

Digital music moved from the musician's toolbox to our everyday computer playlist with the advent of compact disc (CD) technology, developed and refined between 1965 and 1985. It swept the consumer market during the late 1980s and early 1990s, displacing almost completely long-play vinyl albums.

CD Technology CD technology begins with music which itself exists in an analog form, as waves in the air. It then takes these melodious sound waves and translates them into a digital form that is encoded onto the disk. When you play a compact disc, the CD player reads the digital data—a computerized series of zeroes and ones—and translates it back into its original analog form resulting in music you hear via speakers or headphones. So how is it that they get those sounds "burned" onto a music CD that you would buy at the store? Conventional CDs are made up of sandwich-like layers and store the music, or digital data, as a pattern of bumps and flat areas, arranged in a long spiral track. The CD fabrication machine uses a high-powered laser to etch the bump pattern into photoresistant material coated onto a glass plate. Through an elaborate imprinting process, this pattern is pressed onto acrylic or plastic discs. They are then coated with aluminum (or another metal) to create the readable reflective surface. Then, the disc is coated with a transparent plastic layer that protects the reflective metal from nicks and scratches.

When you pop the music disc into your CD player, it guides a small laser along the CD's data track, arranged in a spiral path, starting at the center of the disc. In conventional CDs, the flat areas, or lands, reflect the light back to the laser assembly. The CD player interprets this as a 1. When the beam passes over a bump, the light is bounced away from the optical sensor. The CD player recognizes this as a 0. In conventional CDs, these 1s and 0s are represented by millions of tiny bumps and flat areas on the disc's reflective surface. The bumps and flats are arranged in a continuous track that measures about 0.5 microns (millionths of a meter) across and 3.5 miles long.

Recorded Music—a Creation of the 20th Century; Digital Music of the 21st Century
Popular music, that which is recorded and shared by loads of fans, is no stranger to change. About every 20 years, the experts say, a new technology comes along and completely changes the music industry. Who remembers 33 rpm albums these days? How about 8-track? Laser Disk? Cassette? Or Super Metal-Oxide Cassette? Hidden in basements all over the country surely are copies of Pink Floyd's "Dark Side of the Moon," in all these various outdated formats. The changes continue today. For $500, aspiring musicians can turn a laptop computer into a recording studio. Just 20 years ago, similar equipment would have cost tens of thousands of dollars.

New technologies make their mark on music in two ways, experts say: They alter the sound of pop—what (sounds) musicians can make and listeners can hear—and/or they change the economics of recording and distributing music.

Question 2: Do You Know The Difference Between An MP3 And A WAV File?
 OK. So the fancy MP3s are getting all the hot press and people are talking about the WAV format like it's a dead thing. Not so. Both work really well. It's sort of like what kind of car you want to drive—a flashy new Italian sports car or that old dependable family mini-van in the garage. Both have their merits.

WAV An older music format, WAV was designed by Microsoft to play snippets of sound on any audio-enabled computer. Since Windows 3.1, WAV has been the native format for sound within the Windows environment. As a result, WAV files abound on the Web, and almost every browser has built-in WAV playback support. The WAV file format is very basic. Unlike MP3 and other compressed formats, WAVs are exact digital replicas of the original sound. They're unwieldy, but simple; any computer can play them, and they sound fine. WAV is not an acronym like MP3 or MIDI. It is actually a wave file, referred to as WAV because of the file name extension (.wav).

MP3 Stands for Moving Picture Experts Group, Audio Layer III The MPEG process compresses a sound sequence into a very small file, while retaining its original quality. It performs this magic by being very selective and eliminating certain sound frequencies that can't be heard by the human ear. The format compresses the file to approximately one-twelfth the size of the original file, making it quicker to download or share with a friend. MP3s require special players but are better suited for swapping songs over the Web. WAVs work better for audio-enhanced Web sites.


Enter MP3—The Record Industry's Killer (Application)
There is no single technology that has challenged and threatened the livelihood of the music industry like the advent of the MP3 standard. And, frankly, it is one of the Web's most unlikely heroes.

Nipper the dog
Nipper the dog, born in 1884 in Bristol, England, became the trademark for Victor and other record companies.
MP3 is a compression format that shrinks audio files with only a small sacrifice in sound quality. MP3 files can be compressed at different rates, but the more they are scrunched, the worse the sound quality. A standard MP3 compression is at a 10:1 ratio and yields a file that is about 4 MB for a three-minute track. The digital storage of music is not a new idea, having been brought to the mass market with the advent of CDs in 1978 by Philips. The problem was that a relatively large amount of computer storage space was required for CD quality audio. In 1989, the Fraunhofer Institute in Erlangen, Germany, was granted a patent for the MP3 software compression standard which allowed digital audio to be compressed to approximately one-tenth the size of the original. Although it was technically a lossy compression standard, MP3 took advantage of some peculiarities of human hearing to make the compressed version sound identical to the original. Lossy compression is a technique that does not decompress data 100% back to original. In other words there is a certain amount of loss when the files are restored.

But the real trick was the size of the files. The MP3 breakthrough compressed the large audio files just enough to allow for easy transmission over modem-speed connections. More significant, the specifications were made freely available as a public domain standard. By contrast, other digital audio formats—considered more efficient than MP3—are proprietary formats, developed by companies like Lucent and Microsoft, which have restrictions on how outside developers can employ their technology.

Frauenhofer also developed the first MP3 player in the early 1990s, but it turned out to be less than popular. In 1997, a developer at Advanced Multimedia Products named Tomislav Uzelac created the AMP (Advanced Multimedia Products) MP3 Playback Engine—regarded as the first prime-time MP3 player. Shortly after the AMP engine hit the Net, a couple of university students, Justin Frankel and Dmitry Boldyrev, took the AMP player, added a Windows interface and dubbed it "Winamp." In 1998, when Winamp was offered up as a free music player, the MP3 craze began. Winamp, the latest version is called Winamp 5.0+, is a kind of media player (or interface) which can play back digital audios or files like MP3, RealAudio and Windows Media Audio. Besides VCR-like functions such as playing, pausing, stopping, rewinding and forwarding, some common functions include playlisting, tagging format support and equalizer.

Soon programmers jumped in to create a whole tool box for MP3 junkies. New encoders and players were sprouting everywhere. Search engines made it even easier to find the specific MP3 files people wanted, and portable players let them take MP3 tracks on the road.

Like the unyielding drummer's downbeat on an old Aerosmith song, the story about digital music, free downloads and the Internet leads to one single Killer Application: Napster. And to the courthouse. But, first let's talk about Napster, which hit the Internet in 1999 and allowed anyone with a connection to find and download just about any type of popular music they wanted, in minutes. By connecting users to other users' hard drives, Napster created a virtual community of music. It was cool. Stuff was free. And it was very illegal.

Question 3: How Does An MP3 Player Work?
 The MP3 format is a compression system for music. A 32-megabyte (MB) song on a CD compresses down to about 3 MB on MP3. This lets you download a song in minutes rather than hours, and you can store 10 to 20 songs on an MP3 player using a relatively small amount of memory. But, really the MP3 player is a wonderful example of a new use of existing technologies. None of the components in a typical MP3 player is radical, or even new, technology but a deft combination of existing components.

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 computer chip that tells it exactly how to process the audio. When you hit play, the chip pulls the song data from memory, applies any special effects, or equalization, and streams it to the amplifier. It also runs a decompression algorithm that undoes the compression of the MP3 file and then a digital-to-analog converter turns the bytes back into waves, which you hear as music.
Victrola is the brand name for this line of internal horn phonographs
Victrola is the brand name for this line of internal horn phonographs made from 1906 to 1929
So here comes the Recording Industry Association of America (RIAA), a record company consortium, which sued mostly college students for sharing files, saying that free music was overwhelming the industry and reducing the earning potential of artists who depend on it. MP3 itself is not an illegal format, but when people offer up MP3 versions of copyrighted material, they are breaking the law. RIAA made examples of people serving out large numbers of copyrighted songs. The RIAA has said it won't target people downloading songs, but it has no mercy for those posting large numbers of songs on a site for download.

So how do you download MP3 songs legally and convert them into CDs you can play in your car? Or on the home stereo?

There are three simple steps to creating a CD from MP3 files.

1. To start, 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 or look to our Links page for other cool music sites.

2. As we mentioned earlier, an MP3 file is a compressed version of a CD track. You will 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.

Last, you collect all of the CD tracks together in a directory and write them to a recordable 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.

Portable Music: Is That A Tune In Your Pocket?
So, will the RIAA and the courts be able to drive out MP3s and downloadable music? Probably not. The magic genie is out of the bottle to stay. The future isn't all that hard to see, says Dr. David Foster, who was part of the team that pioneered the storage mechanisms for Apple's original iPod player. Foster, who now works at audio giant Gibson Audio, was hooked on portable music from the very first note.

"It really hit when I got the first iPod," Foster says. He traveled to Asia on business a lot and loaded up tunes on a portable player. But he always exhausted his traveling music store before he got home. With the 5-gig iPod, that was no longer a problem. "It was a really big thing," he says. However, Foster is not quick to declare the CD dead, like many others. Downloadable music is changing the way people get their tunes, though.

Nearly twice as many MP3 files were downloaded last year as the equivalent amount of music sold in CD. If all these transactions had taken place in the US, this translates to roughly 20 CDs downloaded for free in every US household last year, compared with only 10 CDs purchased.

Let's just look at what Steve Jobs and Apple Computers did with iPod and iTunes. At last account, music fans have purchased and downloaded more than 250 million songs from the iTunes Music Store. iTunes users are now downloading one and a quarter million songs per day, which is an annual run rate of almost half a billion songs per year.

Fun Stuff: Satellite Radio.
 Let's not forget about radio. Many people have favorite radio stations that they preset into their car, flipping between them as they drive to and from work or bopping around town. But when cars travel too far away from the source station, the signal breaks up and fades; most radio signals can only travel about 30 or 40 miles from their source. On long trips, signals are constantly fading in and out. Satellite radio has changed all that. Satellite radio broadcasters, such as XMRadio and Sirius Satellite Radio, deliver crystal-clear music transmitted from thousands of miles into space. They broadcast their signals from more than 22,000 miles (35,000 km) away directly into your car via small roof-mounted antennas or into portable radio receivers. (See TechXtra Issue #1, which covered satellite radio technology.)


"Clearly we are in the downloadable music age," Foster says. "I personally don't believe CDs will be dead for years to come. Some people will like to have something physical in their hands when they buy music." Gibson is working on the new Wurlitzer digital jukebox, a personal digital player with a massive hard-drive storage capacity and new snazzy 3.5-inch color screen user interface. They should make downloading and listening to music even easier, he says.

An iPod mini
An iPod mini. The MP3 Player allows you to carry thousands of songs with you and has become the portable audio device of choice. (Photo courtesy of Apple)
Foster, who was educated at Oxford University in England, can see a future when personal portable players will be everywhere. Cars and home entertainment systems will automatically download the newest songs from a pre-programmed playlist and update your personal device every day. Driving in your car or just coming back home will trigger the update so you won't be spending time downloading music all the time. People will still purchase music digitally, but the devices will allow access to that music almost anywhere.

In the future, we won't be quite so tethered to our devices with the help of these emerging technology applications that are just around the corner. Very soon, we will really be able to carry all of our tunes in our pockets, Foster says.

And, we can't ignore the larger question: "How has technology changed music for the musicians, the people who actually produce the music?" Although technology may have changed music distribution, the making of music isn't all that different, says Tim Summers, a violinist and software developer at the University of Virginia. Making music is still the process of one person, or group of people, playing their individual instruments.

Sure enough, technology gives the musician more tools than ever before. Practicing music has changed, as well as how you can look at the past recorded music sessions on your computer. And, the technology can allow a musician to sit at a computer keyboard and combine a number of different tracks to make herself sound like a small orchestra. But, it's still one dude playing. "It's easy to get bogged down with all the sounds you can make in technology and forget the reasons you are making them," he says.

Check out the NSTEP Web site www.nstep-online.org and click on TechXplore program and competition that connects teams of students with scientists and high-tech companies to explore the world of technology. If you want to create a TechXplore team at your school to explore digital technology, send an email to TechXplore@nstep-online.org.

TechXplore is a registered trademark of the National Science & Technology Education Partnership.

XtraReal People

Tim Summers Name: Tim Summers

Age: 32

Title: Software developer for math/science education at the Curry School, Center for Technology and Teacher Education, University of Virginia.

Affiliations: UVA. He's also the music director for the annual Chamber Music Festival in Charlottesville, VA, where the university is located.

His real job: He develops math software for teachers to use in their classes. Using the computer, he presents difficult math problems in a three-dimensional way using high-tech graphics, making them easier to understand. Much of his work revolves around illustrating profit-and-loss problems.

Why he chose this career: He is fascinated with computers and the job allows him the freedom to pursue his music. Tim started playing the violin at age 4 and he was trained at the prestigious Juilliard School. But, he's sought out a wide range of experiences in his life. He first got a college degree in English before taking on the master's program at Juilliard with his violin. His job also allows him to take a large role in the Chamber Music Festival and "play his own gigs," of his own choosing. If he didn't have the computer job, he said he probably would be forced to play more often, at places he didn't necessarily like and it wouldn't be as much fun.

School: BA, English-American Poetry 1995, Harvard University; Master's Degree in Music-Violin Performance, Juilliard School, New York City.

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Was he a math/science wiz in high school? "In high school I did a lot of math," he says. But, by the time he entered Harvard, he had forgotten a good bit of it and wound up taking English courses. But that was cool, he says. Poetry was a way to study language and how it could be applied to music and lyrics. "I was never great in biology but good in physics," he says.

What he does for fun: He plays tennis and enjoys his music. He also is a good cook and makes a mean tomato and cantaloupe spaghetti sauce. "Really, it's very good," he says.

If you have a favorite sport, what is it? Tennis. "But I grew up in Pittsburgh and I've always liked the Steelers."

Advice: "If you have questions, ask them. There are a lot of interesting things to do in science, don't be intimidated." As far as classes to take, he advises to "concentrate on basics and on things you didn't think you might be interested in," he says, adding that students should take as much writing as possible to develop their writing skills. The simple act of writing your thoughts down helps you to sharpen your thinking skills and will make you a better student, he says. "Your thoughts are not as clear as you might think," he says. Also, don't forget to enjoy the pure beauty of mathematics and how it all can sometimes fit together perfectly. "It is easy to get caught in all the symbols and miss out on how it inter-locks," he says.

Gazing at the crystal ball: "I feel in the future we will become more comfortable making arrangements between the digital world and the acoustic (non-digital) world. The fact is we like digital things and we like real things. But, the problem is that digital music can seem unreal. And, it's hard for a musician to make acoustic instruments sound good. I think we'll figure some hybrid between them."

Music Technology Links
    General Digital Music Sites
  • Bregman Electronic Music Studio at Dartmouth College.
  • The Center for Computer Research in Music and Acoustics Stanford University music research site.
  • The Center for New Music and Audio Technologies (CNMAT) Popular Berkeley University music research site that draws participants from many Berkeley University departments.
  • CREATE Center for Research in Electronic Art Technology, University of California, Santa Barbara.
  • CEMI Center for Experimental Music and Intermedia, University of North Texas.
  • EMUISC-L A Weblog that has a plethora of archived information.
  • Electronic Music Foundation A Web site dedicated to electronic music.
  • IEEE/electronic music Computer Society/Institute of Electrical and Electronic Engineers' Web site on Computer Generated Music (CGM).
  • ICMA International Computer Music Association.
  • InternetDJ Independent music community with large archive of music.
  • Glossary A fine collection of definitions for digital music terms.
  • MusicMedia Science at the University of Zurich.
  • Obsolete.com A collection of historical electronic instruments from 1870-1990, with some sound files.
  • Other Minds A global New Music community where composers, students, and listeners discover and learn about innovative music by composers from all over the world.


    • Fun Stuff
  • A1freesoundeffects.com Download free WAV files that feature movie and television sound effects.
  • Moviesounds.com A Web site dedicated to sounds from the movies, from the classic Disney fantasy Tron to Silence of the Lambs.
  • Umixitmusic.com UmixIt allows the average person to share the studio experience with an actual recording artist. UmixIt provides the user with the isolated audio tracks direct from the actual recording session used to make the artists album.
  • WavSite is a searchable database of over 4300 movie sounds (wav files) from over 150 movies, cartoons, and TV show episodes.
  • Yahoo Sounds A Yahoo directory of fun sounds from the movies and television.


    • MP3 Websites
  • Audio Grabber High quality CD ripping software includes free download.
  • Dailymp3.Com Daily MP3 software updates.
  • IUMA Internet Underground Music Archive with lots of cool music.
  • Mpeg.Org Reference site for MPEG and MP3.
  • MP3 CD Burner Site focusing on burning (or copying) software.
  • MP3.com Download licensed MP3s at this great resource site.
  • MP3 Place Everything you wanted to know about MP3s.
  • Shoutcast Nullsoft's Free Winamp-based distributed streaming audio system that allows you to hear radio broadcast music through the computer.
  • Wired News Wired's ongoing take on all this MP3 business.
  • ZDNET Digital Audio A good site for news about developments in Internet music.


    • Hardware/Software
  • Apple's iPod Apple's iPod and iTunes Web site.
  • Gibson's Wurlitzer Digital Jukebox The Web site for Gibson's MP3 Wurlitzer Digital Jukebox.
Music Technology Glossary

Time (or absolute time): In an audio CD, the time elapsed since the beginning of the disc. It can be used in determining the start and stop times of sound segments for programming an application on a mixed-mode disc.

Advanced Audio Coding: (AAC) An extension of MPEG-2 Audio Layer 3 NBC (non backward compatible). It can encode with greater quality than MP3. It also supports multi-channel audio including LFE (low-frequency effects channels used in movies) and sounds better than Dolby Digital movies and DVDs.

Advanced SCSI Programmer's Interface: (ASPI) A layer of code that manages communication between software and SCSI cards.

Authoring: What you do to create an application that may eventually be stored on CD.

Bit: A single binary digit, either 0 or 1. A bit is the smallest unit of data stored in a computer; all other data must be coded into a pattern of individual bits. A byte represents sufficient computer memory to store a single character of data, and usually contains eight bits. For example, in the ASCII code system used by most microcomputers the capital letter A would be stored in a single byte of memory as the bit pattern 01000001. The higher the number of bits a computer can process simultaneously, the more powerful the computer is said to be.

Compact Disc-Recordable: (CD-R) When referring to recordable discs (media), "CD-R" is often used to refer to write-once discs, in contrast to CD-RW. See also Recordable Disc.

Compact Disc-Read Only Memory: (CD-ROM) A standard for compact disc to be used as digital memory media for personal computers.

CD-ReWritable: (CD-RW) CD recordable media that can be erased and re-recorded. CD-RW media can only be written in a CD-RW recorder, not in a normal CD recorder, though a CD-RW recorder can also record standard CD-R discs.

CD-Quality Sound: Digitized sound. It was designed to be the minimum standard required to reproduce every sound the human ear can hear. Most audio CDs are recorded to this level.

Data Compression: Techniques for reducing the amount of storage needed for a given amount of data. They include word tokenization (in which frequently used words are stored as shorter codes), variable bit lengths (in which common characters are represented by fewer bits than less common ones), and run-length encoding (in which a repeated value is stored once along with a count). There are two main forms: In lossless compression the original file is retrieved unchanged after decompression. Such compression is necessary for documents; some types of data (sound and pictures) can be stored by lossy compression where some detail is lost during compression, but the loss is not noticeable. Lossy compression allows a greater level of compression. The most popular compression program is PKZIP, widely available as shareware.

Digital: In electronics and computing, a term meaning "coded as numbers." A digital system uses two-state—either on/off or high/low voltage—pulses to encode, receive, and transmit information. A digital display shows discrete values as numbers (as opposed to an analogue signal, such as the continuous sweep of a pointer on a dial).

Digital Audio Extraction: (DAE) The preferred method of making MP3s by taking music from a digital source (CD) and capturing it digitally. This process is also known as "ripping."

Digital-To-Analogue Converter: Electronic circuit that converts a digital signal into an analogue (continuously varying) signal. Such a circuit is used to convert the digital music output from a computer into the analogue voltage required to produce sound from a conventional loudspeaker.

DAT: Digital Audio Tape.

Digital Electronics: The technology that underlies digital techniques. Low-power, miniature, integrated circuits (chips) provide the means for the coding, storage, transmission, processing, and reconstruction of information of all kinds.

Digital Recording: Technique whereby the pressure of sound waves is sampled more than 30,000 times a second and the values are converted by computer into precise numerical values. These are recorded and, during playback, are reconverted to sound waves. The numerical values converted by the computer represent the original sound-wave form exactly and are recorded on compact disc. When this is played back by laser on a CD player, the exact values are retrieved. Then, when the signal is fed via an amplifier to a loudspeaker, sound waves exactly like the original ones are reproduced.

Extent: A sequential set of sectors in which a file or portion of a file is recorded.

EQ: (equalization) It also refers to electronic of software devices, called equalizers, which are employed to bring the relative balance of the frequencies back to their original form. Equalizers are also used in almost all areas of audio, including broadcasting.

File System: A data structure that translates the physical (sector) view of a disc into a logical (files, directories) structure, which helps both computers and users locate files. In other words, it records where files and directories are located on the disc.
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 		ISO 9660 Format: The most common international standard for the logical format for files and directories on a CD-ROM. Some other common logical formats such as Joliet and Rock Ridge are extensions of ISO 9660. The cool thing about ISO 9660 is that it's compatible with most systems, so the same disc can contain both Apple Macintosh and PC versions.

ISO 9660 Interchange Levels: Methods of recording and naming files on disc under the ISO 9660 standard. There are three levels:
  • Level 1 (the lowest common denominator) Each file must be written on disc as a single, continuous stream of bytes (called an extent). A filename may not contain more than eight decimal characters.
  • In Level 2, again, each file must be written on disc in a single extent, filenames may be up to 255 characters long.
  • In Level 3 a file may be written in multiple extents, so it is used for packet writing. Filenames may be up to 255 characters long.


    • Jewel Case: The hinged plastic case, often brightly colored, in which CDs are often stored.

    Killer Application: (Killer App) A program so good or so compelling to potential users that they buy the computer that the program runs on for no other reason than to be able to use that program. Killer applications are very rare. The World Wide Web is the killer application for the Internet by bringing visual excitement and ease of use.

    Mastering: Technically, it refers to the process of creating a glass master from which compact discs will be reproduced in quantity. In desktop recordable CD systems, mastering is done with a desktop CD recorder and the term is generally used to mean "recording."

    Media: Recordable media—blank CD-R or CD-RW discs.

    Mixer: In sound recording, equipment that allows an engineer to set a different volume level for each individual sound track so that solos can be highlighted and loud instruments can be kept from dominating softer ones. Multimedia computer systems that allow recording generally include similar, though not as sophisticated, functions through software.

    Motion Picture Experts Group: (MPEG) An international standards organization responsible for the MPEG 1 and MPEG 2 standards for the compression of full-motion video, as well as the MPEG 3 standard.

    Optimum Power Calibration Area: (OPC Area) A special area near the center of the recordable disc. Before writing a track on a disc, the CD recorder must adjust the amount of power applied to the writing laser to an optimum level for each individual disc. The optimum calibration area is reserved for this purpose.

    Program Memory Area: (PMA) On a recordable disc, an area which "temporarily" contains the Table of Contents information when tracks are written in a session that is not yet closed.

    Premastering: The process of preparing data to be recorded onto a compact disc. This includes dividing the data into sectors and recording those sectors with the appropriate header (address) and error correction information. In the case of recordable CD systems, premastering and mastering are done in one operation, resulting in a ready-to-read compact disc.

    Random Erase: The ability to erase a single file at a time from a CD-Re-Writable disc, freeing up disc space for immediate re-use, just as you would do on a hard or floppy disk.

    Recordable Disc: The media used in recordable CD systems. The blank disc is made of a bottom layer of polycarbonate, with a preformed track spiral which the recording laser follows when inscribing information onto the disc. A translucent layer of recordable material is laid on top of the polycarbonate, then a reflective layer (gold or silver colored). On top there is a thin layer of lacquer and sometimes a printed label. The standard recordable disc is "write-once"—data written to it cannot be erased, although it is possible to add data in a later session. For erasable/rewritable discs, see CD-RW.

    Sampling: Measurement of an analogue signal (such as an audio or video signal) at regular intervals. The result of the measurement can be converted into a digital signal that can be electronically enhanced, edited or processed.

    Small Computer System Interface: (SCSI, pronounced "scuzzy") An interface that allows up to seven peripheral devices to be linked to a single controller. It is a standard method for connecting peripheral devices (such as printers, scanners and CD-ROM drives) to a computer. A group of peripherals linked in series to a single SCSI port is called a daisy-chain.

    Track: Every time you write to CD, you will create at least one track, which is preceded by a gap. Any session may contain one or more tracks. Multiple tracks within a session may be of the same or of different types—for example, a mixed-mode disc contains data and audio tracks—though it is more common for multiple tracks within a single session to be all audio tracks.

    WAV: Audio file format for IBM-compatible PCs, widely used to distribute sounds over the Internet. WAV files, which contain a digitized recording of a sound, bear the suffix .wav—hence the name WAV file.

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