Audio and Music Gadgets

1. 5 Types of Microphones
2. Headphone Earmuffs
3. Headphone Hats
4. Noise-canceling Headphones
5. Portable Audio Studios
6. Portable media Centres
7. Tape Recorders
8. The Reactable
9. What causes that howling sound inPA Systems?
   

What causes that howling sound in PA systems?

A simple PA (public address) system consists of a microphone, an amplifier and one or more speakers. Whenever you have those three components, you have the potential for feedback. Feedback occurs when the sound from the speakers makes it back into the microphone and is re-amplified and sent through the speakers again, like this:

Imagine, for example, that you place the microphone in front of the speaker as shown. Now you tap on the microphone. The sound of the tap goes through the amplifier, comes out the speaker, re-enters the microphone, etc. This loop happens so quickly that it creates its own frequency, which we hear as a howling sound. The distance between the mike and the speakers has a lot to do with the frequency of the howling, because that distance controls how quickly the sound can loop through the system.

You can actually try this out on your computer if your computer has speakers and a microphone. In Windows, you need to enable the microphone and speakers using the volume control (which you can access by double clicking on the speaker icon in the system tray).

Make sure that in this dialog the microphone and speakers are not muted and are at maximum volume (if the microphone control is not visible, select it in Properties). If you have it set up right, you should be able to tap the microphone and hear it in the speakers. Now place the microphone near the speakers and turn up the speaker volume until you hear the feedback. Try changing the distance between the mike and speakers and see what effect that has on things. Be sure not to try this at 2 a.m. when other family members are sleeping, and also be sure to put the dog out...

If you are setting up a sound system and want to avoid feedback, there are a few general rules that can help you avoid the problem:

• Make sure the speakers are in front of the microphone and pointing away from the microphone. If the speakers are behind the microphone, then feedback is nearly guaranteed.
• Use a unidirectional microphone.
• Place the microphone close to the person who is speaking/performing.
• If you have access to an equalizer, dampen the frequencies where feedback is occurring.

The reactable

The reactable is a new music synthesizer that works by placing, moving and arranging blocks on top of a table to generate different sounds.

Simple blocks are a common symbol of childhood creativity, curiosity and intelligence. Placing building blocks next to or on top of each other allows children to let their imagination run wild and create any number of structures on a playroom floor. If letters, pictures or colors are added to the blocks, children can add words, patterns and other arrangements into their designs.

If we add a table under those blocks, the building process all of a sudden becomes much more collaborative. Although we typically think of a table as a simple object -- one that's useful, but maybe a little static -- it's actually yet another important symbol. Tables can be a fun space, a place where people gather to exchange conversation, ideas and work. Many elementary schools choose to sit classmates around larger, round tables instead of individual tables to encourage cooperation and group work. Tables aren't just for child's play, of course: Experienced architects draw out plans for major construction projects on top of tables, and artists might use tables to construct larger pieces of art.

­Taking the two basic concepts of blocks and tables, four graduate students from the Univesitat Pompeu Fabra in Barcelona, Spain, added music to the mix and designed something called the reactable. The reactable is essentially a music synthesizer, and if you hear it played, it sounds similar to a lot of modern electronic dance music. The difference between the reactable and a typical synthesizer, however, is that participants manipulate sound with blocks on a round table. By rotating or moving the blocks on the table, a person (or several people) can tweak a variety of sounds, beats and notes, creating an electronic soundscape.

In addition to the ease with which you can maniupulate sound, there's also a visual element: The table has a translucent blue surface that lights up with dynamic animations that highlight the musical changes. For musicians and spectators alike, the reactable is a musical instrument that's not only fun to listen to, but fun to watch as well.

Reactable Basics

Icelandic singer Björk performs at the Sydney Opera House in Sydney, Australia, during her world tour in support of her album "Volta." If you look closely at the video screen in the photo, the image is of a DJ tweaking blocks on the reactable.

Although it's bright and flashy on the outside, the reactable is, at its most basic, a music synthesizer, a musical instrument that electronically manipulates notes and tempos, bending and shaping the properties of sound waves. These manipulations create interesting noises and variations on musical notes that musicians can't easily make with regular acoustic instruments like pianos or guitars. By turning a knob on a keyboard synthesizer while holding down a note, for instance, the user can make the pitch of a note bend and waver, making eerie electronic sounds that swell up and down.

­When four students from the Univesitat Pompeu Fabra -- Sergi Jordà, Martin Kaltenbrunner, Günter Geiger and Marcos Alonso -- set out to design the reactable, they did so while keeping a few basic principles in mind. They wanted the instrument to be collaborative: Even though it's possible for one person to play alone, the table is round and allows many people to gather around and interact with the instrument's several blocks. The reactable should also be intuitive and easy to learn, yet challenging to listen to and play. If someone were to walk up to the table without a set of instructions or any guidance, that person should be able to pick up the basics fairly quickly. In other words, anyone, from inexperienced or novice players to seasoned DJs, has the ability to make the reactable sound and look cool, according to its makers.

Björk and the reactable on Tour The reactable has gained popularity over the years through demonstrations at festivals and museums, and it's won several awards, including an Ars Electronica Golden Nica and the Premi de la Cuitat de Barcelona (Barcelona City Award) in 2007. But the technology received its biggest boost when Icelandic musician Björk saw a video demonstration on YouTube. She decided to take the synthesizer and a DJ who could play one on her tour promoting her 2007 album, "Volta," and the reactable became an important visual element to her shows

In the team's words, the reactable is a "novel multi-user electro-acoustic musical instrument with a tabletop tangible user interface" . While it's a bit of a mouthful, the phrase explains the instrument nicely. The reactable is, of course, a multi-user instrument -- a certain number of people stand around the object and, using their hands, create sound by manipulating the blocks. It takes a certain amount of skill to learn, but with enough practice, it's possible to play with ease. Although it's somewhat of an umbrella term, any music that is "electro-acoustic" refers to music that's been produced with the use of electricity. In the case of the reactable, all sound coming from the synthesizer is electronic, and therefore electro-acoustic. The tabletop refers, of course, to the device's surface, and the fact that it's a "tangible user interface" simply means players can manipulate objects by using their hands, twisting and moving the blocks like knobs on a traditional synthesizer.

Once those blocks are placed on the table's surface, what do they do? And how do you know which block is which?

Reactable Objects

When you place one side of an object onto the reactable's surface, it's like pressing a button on a synthesizer and letting a noise or a beat loop over and over again. But just putting down one block would miss the point of the reactable -- there are several types of blocks, with different shapes and sides, and where you place one in relation to another affects the outcome of the music.

The position of each object on the reactable's tabletop surface affects the outcome of the music, giving players a seemingly endless amount of choices.

­There are six different blocks, each with a unique shape and function. Square objects are sound generators -- rotating a generator changes the frequency, and dragging your finger around an animated circle can increase or decrease its amplitude (how loud or soft the sound is), much like controlling the volume on an old television set. A sound can also be cut by making a "cutting" gesture to the line that connects the object with the center of the table, and you can turn it back on by touching the animated circle again.

Squares with rounded edges are sound filters, which process sounds by adding different effects. They perform the same thing a ­guitar pedal might, adding flange, fuzz or feedback-like resonance to the sounds the instrument would normally produce. If you had a sound generator giving off a steady, even tone, adding a sound filter next to it would distort the sound to make it more interesting.

Circular objects are controllers, sending control data to the objects closest to it. This will change the frequency of the sound wave -- for instance, you could either have a steady, flowing sound that goes on cleanly and uninterrupted, or you could vary the frequency and give it more of a wah-wah shape.

Control filters (octagonal, or eight-sided) and audio mixers (pentagonal, or five-sided) are more geometrically complex, and their jobs are in fact a bit more complex. The two types act as samplers and mixers, allowing musicians to create intricate melody loops and lines that harmonize and change shape and key.

Global objects, which are hemispheric, are unique in that they have their own field, which is also in the shape of a circle, that affects every object that falls within that field. They typically provide a metronome, or keep time, for any object they affect or act as a tonalizer, correcting notes created by the sound generators and filters.

Under the reactable Table: reacTIVision

The position of each object on the reactable's tabletop surface is analyzed by the computer vision software underneath known as reacTIVision.

To analyze the positions of the blocks in relation to each other, the reactable uses a computer vision (CV) system located under the tabletop surface. The CV setup is completely hidden within the machine and consists mainly of two important tools -- a camera and a projector.

Both the camera and projector point up toward the bottom of the tabletop, but they each serve a different purpose. The camera, which runs on a special vision engine called reacTIVision, looks up at the blocks and analyzes several factors:

• ­Which sides of the blocks are facing down on the table
• Where the blocks are in relation to the table's center
• Where the blocks are in relation to other blocks
• How the blocks are positioned around their own axis
• Any other tangible adjustments made on the table's surface that might alter pitch, filters and so forth

The reacTIVision engine takes all of these positions into account, analyzes the space and sends the information to a connection manager, which does two things simultaneously. First, it passes the reacTIVision's information to an audio synthesizer, which creates the sounds the musicians are attempting to play and pumps the music out to an output source. At the same time, the connection manager sends that same information to the projector, which also points up toward the underside of the tabletop. This projector isn't taking in information like the reacTIVision camera; instead, it paints the animations onto the blue, translucent tabletop, providing the players and spectators with the appropriate visual cues to match the music coming out.

The students who made the reactable give demonstrations at music festivals, conferences and museums fairly often, so if you want to see a live performance, check the reactable's Web site for upcoming appearances. Of course, if you want to buy one for yourself, there are plans to bring the reactable to the market. (Unfortunately, no one has mentioned a price tag.) If all else fails, you could always check out Björk on tour if she still happens to favor the synthesizer and stops by your area.

Tape Recorders

Magnetic recording is a backbone technology of the electronic age. It is a fundamental way for permanently storing information.

• In the audio realm, magnetic tape (in the form of compact cassettes) is a popular way of distributing music. People either buy tapes pre-recorded with material, or make their own tapes from CDs.
• In the video realm, video tape is used widely both in the broadcast industry and at home to store material for later viewing on VCRs.
• In the computer realm, magnetic recording is used on floppy disks, hard disks and magnetic tape as the main method for data storage.

In this article, we will look at magnetic recording. We'll focus on cassette tapes and tape recorders, but the same technology applies to any form of magnetic recording. You will learn that the reason why magnetic recording is so popular is because it an easy and inexpensive technology with good medium-term (10 to 20 years) storage characteristics.

The Tape

There are two parts to any audio magnetic recording system: the recorder itself (which also acts as the playback device) and the tape it uses as the storage medium.

The tape itself is actually very simple. It consists of a thin plastic base material, and bonded to this base is a coating of ferric oxide powder. The oxide is normally mixed with a binder to attach it to the plastic, and it also includes some sort of dry lubricant to avoid wearing out the recorder.

Iron oxide (FeO) is the red rust we commonly see. Ferric oxide (Fe₂O₃) is another oxide of iron. Maghemite or gamma ferric oxide are common names for the substance.

This oxide is a ferromagnetic material, meaning that if you expose it to a magnetic field it is permanently magnetized by the field. That ability gives magnetic tape two of its most appealing features:

• You can record anything you want instantly and the tape will remember what you recorded for playback at any time.
• You can erase the tape and record something else on it any time you like.

These two features are what make tapes and disks so popular -- they are instant and they are easily changed.

Audio tapes have gone through several format changes over the years.

• The original format was not tape at all, but actually was a thin steel wire. The wire recorder was invented in 1900 by Valdemar Poulsen.
• German engineers perfected the first tape recorders using oxide tapes in the 1930s. Tapes originally appeared in a reel-to-reel format. See this page for a picture of an early reel-to-reel recorder.
• Reel-to-reel tapes were common until the compact cassette or "cassette tape" took hold of the market. The cassette was patented in 1964 and eventually beat out 8-track tapes and reel-to-reel to become the dominant tape format in the audio industry.

If you look inside a compact cassette, you will find that it is a fairly simple device. There are two spools and the long piece of tape, two rollers and two halves of a plastic outer shell with various holes and cutouts to hook the cassette into the drive. There is also a small felt pad that acts as a backstop for the record/playback head in the tape player. In a 90-minute cassette, the tape is 443 feet (135 meters) long.

The Tape Recorder

The simplest tape recorders are very simple indeed, and everything from a Walkman to a high-end audiophile deck embodies that fundamental simplicity.

The basic idea involves an electromagnet that applies a magnetic flux to the oxide on the tape. The oxide permanently "remembers" the flux it sees. A tape recorder's record head is a very small, circular electromagnet with a small gap in it, like this:

This electromagnet is tiny -- perhaps the size of a flattened pea. The electromagnet consists of an iron core wrapped with wire, as shown in the figure. During recording, the audio signal is sent through the coil of wire to create a magnetic field in the core. At the gap, magnetic flux forms a fringe pattern to bridge the gap (shown in red), and this flux is what magnetizes the oxide on the tape. During playback, the motion of the tape pulls a varying magnetic field across the gap. This creates a varying magnetic field in the core and therefore a signal in the coil. This signal is amplified to drive the speakers.

In a normal cassette player, there are actually two of these small electromagnets that together are about as wide as one half of the tape's width. The two heads record the two channels of a stereo program, like this:

When you turn the tape over, you align the other half of the tape with the two electromagnets.

When you look inside a tape recorder, you generally see something like this:

At the top of this picture are the two sprockets that engage the spools inside the cassette. These sprockets spin one of the spools to take up the tape during recording, playback, fast forward and reverse. Below the two sprockets are two heads. The head on the left is a bulk erase head to wipe the tape clean of signals before recording. The head in the center is the record and playback head containing the two tiny electromagnets. On the right are the capstan and the pinch roller, as seen below:

The capstan revolves at a very precise rate to pull the tape across the head at exactly the right speed. The standard speed is 1.875 inches per second (4.76 cm per second). The roller simply applies pressure so that the tape is tight against the capstan.

Tape Types and Bias

Most higher-end tape decks have controls like those below for different tape formulations and bias.

Most higher-quality tapes tell you their formulation by stating a type. There are four types of tape in common use today:

• Type 0 - This is the original ferric-oxide tape. It is very rarely seen these days.
• Type 1 - This is standard ferric-oxide tape, also referred to as "normal bias."
• Type 2 - This is "chrome" or CrO₂ tape. The ferric-oxide particles are mixed with chromium dioxide.
• Type 4 - This is "metal" tape. Metallic particles rather than metal-oxide particles are used in the tape.

Sound quality improves as you go from one type to the next, with metal tapes having the best sound quality. A normal tape deck cannot record onto a metal tape -- the deck must have a setting for metal tapes in order to record onto them. Any tape player can play a metal tape, however.

The controls on the tape deck let you match the recording bias and signal strength to the type of tape you are using so that you get the best sound possible.

Bias is a special signal that is applied during recording. The first tape recorders simply applied the raw audio signal to the electromagnet in the head. This works, but produces a lot of distortion on low-frequency sounds. A bias signal is a 100-kilohertz signal that is added to the audio signal. The bias moves the signal being recorded up into the "linear portion" of the tape's magnetization curve. This movement means that the tape reproduces the sound recorded on it more faithfully. Several of the links on the next page go into this topic in detail, and also cover Dolby noise-reduction systems.

Portable Media Centers

In our increasingly mobile society, portability is king. Thanks to easy-to-transport, high-tech products such as cell phones, laptops, personal data assistants and portable MP3 players, many of the tasks that can be accomplished at home on a personal computer can now be done on the road.

The iriver PMC-140 has a 40-GB storage capacity.

With portable media centers, you can store and access nearly all of your digital entertainment files on a single, lightweight unit about the size of a paperback novel. They can handle recorded television programs, movies, home videos, music and digital photos. You can even connect a portable media center to a television or stereo using the A/V-out jack when portability isn't necessary.

In this article, you'll learn about the storage capacity and wide array of advanced features available in portable media centers.

Storage Capacity and File Types
Windows Mobile-based portable media centers currently feature 20-GB or 40-GB storage capacities and can store and play not only music and photos, but also video content. A portable media center with a 40-GB hard disk can hold up to 160 hours of video, up to 10,000 songs or tens of thousands of digital photographs. Archos currently offers non-Windows portable video player/recorders with similar capabilities to the Windows PMCs, but Archos' players feature up to 100 GB (400 hours of video) of storage.

File Types
Windows Mobile-based portable media centers support a wide variety of different file types, including the following:

• Microsoft Windows Media Video and Microsoft Photo Story files (.wmv and .asf) at a resolution of 320x240 pixels and a bit rate that is less than 800 kilobytes per second (Kbps)
• Microsoft Windows Media Audio files (.wma)
• MP3 audio files (.mp3)
• JPEG image files (.jpg, .jpeg, .jpe, .jfif)
• Microsoft Recorded TV Show files (.dvr-ms)
• MPEG movie files (.mpeg, .mpg, mpe, .m1v, .mp2v, and .mpeg2)
• Microsoft Windows Video files (.avi)
• Microsoft Windows Audio files (.wav)

Windows Media Player 10 has the built-in capacity to convert oversized Windows Media Video files and JPEG pictures into a format and size that the PMC can handle. Windows Mobile-based portable media centers are not compatible with iTunes music files.

Adding Music and Video to a PMC

Using Windows Media 10, you can transfer files from a personal computer to a portable media center through a USB 2.0 cable. Windows PMCs will accept the following types of files from a home computer or laptop:

• Music copied from a CD
• Pictures from a digital camera
• Home movies from a digital video camera
• TV shows recorded on a computer running Windows XP Media Center Edition or other personal video recorder programs
• Videos downloaded from the Internet

The Samsung Yepp YH-999 PMC can store 20 GB of music, movies and photos.

Portable media centers can also play premium downloaded digital music and video from various online services. It should be noted, however, that DVDs you own cannot be transferred to the device because of copyright restrictions.

Transferring Files
Files can be transferred from a personal computer to a portable media center using Windows Media Player 10. If the portable media center cannot support a particular file size or format, Windows Media Player 10 will automatically convert the file to a type and size supported by the device. You can set up Windows Media Player 10 to sync the type of media you want every time you connect a portable media center to your PC.

The file-synchronization process using Windows Media Player 10 is fairly straightforward:

1. Install Windows Media Player 10 on your PC.
2. Use the USB 2.0 cable that came with your PMC to connect the portable media center to your PC.
3. Windows Media Player automatically detects that a portable device is attached and asks whether you would like to sync the device using Windows Media Player.
4. Click OK to run through the setup.
5. The Sync Wizard opens and gives you the opportunity to configure the sync settings. Accept the default settings if they look good to you, and click Finish.*
6. If a Security Upgrade Required dialog box appears, click OK to accept the upgrade.
7. Windows Media Player syncs all selected audio, video, recorded TV and image files to the portable media center, including album art for CDs. Windows Media Player may convert some files into an appropriate format for playback on your portable media center. Syncing takes anywhere from a few seconds to several hours, depending on the number and size of files.**
8. When synchronization is complete, the "Items to synchronize" panel will show the number of items that have been synchronized.
9. Unplug the cable. The device returns to the home screen.

*If you like, you can change the sync settings in Windows Media Player so that only specific types of media files (e.g., music files or photos) will sync each time you connect the portable media center to your PC. To change the sync settings in Windows Media Player, click the Sync tab, and then click the Sync Settings button. The new dialog box that appears allows you to choose the files that you want to sync when you connect the portable media center to your PC. The default setting automatically syncs all available media files.

**File conversion may be necessary for some audio and video files to make them compatible with your portable media center. To adjust media file-conversion settings, go to Tools>Options in Windows Media Player 10. The dialog that displays conversion settings is on the Devices tab. To speed up the sync process for large files, you can choose to allow Windows Media Player to convert audio and video files during computer downtime.

Windows-based Portable Media Centers

There are three major brands of Windows Media-based portable media centers currently on the market:

Creative Zen Portable Media Center

• Manufacturer: Creative Labs
• Storage capacity: 20 GB
• Dimensions: 5.67 x 3.18 x 1.06 inches (14.4 x 8.1 x 2.7 cm)
• Display size: 3.8 inches (9.7 cm)
• Resolution: 320x240
• Weight: 11.3 ounces (320 grams)
• Battery life: Up to 22 hours continuous audio playtime or up to seven hours continuous video playtime
• Price: MSRP $499

Creative Zen 20-GB Portable Media Center

iriver PMC-120 (20 GB) and PMC-140 (40 GB)

• Manufacturer: iriver
• Storage capacity: 20 GB or 40 GB
• Dimensions: 5.6 x 3.3 x 1.2 inches (14.2 x 8.4 x 3.0 cm)
• Display size: 3.5 inches (8.9 cm)
• Resolution: 320x240
• Weight: 45 ounces (1.3 kg)
• Battery life: Up to 14 hours continuous audio playtime or up to five hours continuous video playtime
• Price: MSRP $499 or MSRP $649

iriver PMC-120

Samsung Yepp YH-999 Portable Media Center

• Manufacturer: Samsung
• Storage capacity: 20 GB
• Dimensions: 3.82 x 4.21 x 0.83 inches (9.6 x 10.6 x 2.1 cm)
• Display size: 3.5 inches (8.9 cm)
• Resolution: 320x240
• Weight: 8 ounces (227 grams)
• Battery life: Up to 12 hours continuous audio playtime or up to three hours continuous video playtime
• Price: MSRP $499

  Samsung Yepp YH-999 PMC

  
  

  Alternatives to Windows Media Players

  There are also non-Windows-based portable media players currently available -- for example, the Archos AV420 (20 GB), AV480 (80 GB) and the new AV4100 (100 GB) Pocket Video Recorders.

  Photo courtesy Consumer Guide Products Archos AV420 Pocket Video Recorder

  One advantage of the Archos players is the dramatic increase in capacity. Another major advantage is that television programs and movies can be recorded directly from TV, VCR or cable/satellite; with Windows Mobile-based portable media centers, a PC running Windows XP Media Center must serve as an intermediary in the video transfer process. A downside to the Archos players is that you don't have the benefit of Window's Mobile's incredibly simple, automatic file-sync process.

  A robust challenger in the portable media player arena is the Sony PlayStation Portable (PSP). The PSP is a lightweight, pocket-size gaming device that utilizes a broad range of digital content. The PSP features a 16:9 widescreen display, USB 2.0 and 802.11b WiFi LAN connectivity and the ability to play games, video and MP3 audio.

  In addition, there is increased competition between Windows Media-based portable media centers and Apple iPod media players. Apple's latest iPod supports up to 150 hours of video and is available in 30 and 60 GB models. Apple already has network deals to provide downloadable TV shows, and it is in talks with TiVo to allow for coordination between home DVRs and iPods.

  The Future of Portable Media
  Will portable media centers be a hit with today's on-the-go consumers? Only time will tell. Although Windows-based portable media centers are larger and heavier than MP3 players such as the Apple iPod, they offer larger screens, a familiar Windows-based interface and more diverse media content. The future promises more video and audio content designed specifically for portable media centers. Some of these new features include the following:

• TiVoToGo - With this new feature, TiVo subscribers will be able to transfer television programs to a Windows XP-based PC. Then, they can use Windows Media Player 10 to transfer their favorite shows to a portable media center.

• MSN video downloads, including videos from CNBC, MSNBC, Fox Sports and Food Network - These videos, which are stored in a Windows Media Player 10 library, can be easily synchronized with portable media centers.

• MTV, VH1, CMT and Comedy Central programming for portable media centers, including news content and musical performances

If portable media centers prove popular with consumers, we can expect to see even greater storage capacity and sleeker and lighter designs.

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Portable Audio Studios

Just a couple of decades ago, if a band wanted to record an album, it only had a few options. Some artists would rent time in a professional recording studio filled with expensive equipment. Others would invest in personal recording studios, either building new structures or converting existing ones into studio space. Building a personal studio can be very expensive, and the space has to be large enough to hold all the equipment needed to produce high quality recordings.

Recording Technology Image Gallery

Traditional recording studios include large mixing boards and other bulky equipment.

Today, computers and advanced technology make creating a personal recording studio more accessible and affordable. And unlike the large recording studios of the past, you can take these on the road with you. Some bands, like They Might Be Giants, record many of their live performances and make them available to purchase later. The recording studio has gone portable.

Not only can musicians and audio engineers carry around their own recording studios, they can more easily afford their own equipment. A professional recording studio might cost tens of thousands of dollars to construct and bring online. A portable studio can cost a fraction of that. Still, you get what you pay for. If a band chooses to skimp on certain equipment, it might find that the recordings it produces aren't of the best quality.

Magnetic tape recorders served as early portable recording studios.

Recording on the Go In a way, portable studios aren't a new thing. The cassette tape made it possible for just about anyone to make a recording. A musician with a tape deck and a microphone could record a few tracks on his or her own. But such a simple setup gives musicians very few options. A state-of-the-art portable studio gives musicians much more control over the finished product.

The components of a port­able studio are very similar to a traditional recording studio's equipment. But a portable studio tends to assign multiple production tasks to a single device so that only a few pieces of equipment handle the same duties as a studio full of gear. And just because a studio is portable doesn't mean you can pop it into your pocket. Depending on the components involved, a portable studio might require an audio engineer a few trips back to the van to carry it all inside.

What kind of equipment would you find in a portable studio? Keep reading to find out.
­

Portable Audio Studio Hardware

The most important piece of equipment in any portable studio is the digital audio workstation (DAW), also known as a computer. Depending on the software on the computer, a DAW could act as a recording device, mixer and sequencer. By handling so many tasks, a good DAW reduces the need for additional equipment.

A simple portable recording studio.

Handling audio files requires a lot of computer horsepower, particularly if you're mixing lots of channels. For that reason, it's important to choose a computer with a fast microprocessor. For a while, it seemed like Mac computers would always reign supreme in the world of media computing. But some audio engineers say that the differences between Mac and PC performance are negligible. As long as the computer you pick has a powerful CPU and a large, fast hard drive, you're in good shape.

Channels and Mixing

You've probably heard terms like 4-channel or 16-channel devices. What does that mean? In general, it means the equipment can accept a certain number of individual input devices when recording. A 4-channel device can accept four inputs, for example. In recording, each channel remains separate from the other channels. That's where a mixer comes in. Audio engineers use mixers to tweak each channel before combining all inputs into a single recording.

Another piece of the portable studio setup is the audio interface. While many computers have input and output ports and sound cards, they aren't always capable of recording or playing back professional-quality sound. For that reason, many engineers who set up portable studios rely on additional audio interface devices. These devices range in size from a handheld gadget to a machine the size of a hefty VCR.

Audio interface devices usually have multiple input and output ports. Many have both analog and digital ports, which covers all musical instruments and microphones. Some also act as analog-to-digital converters (ADCs). That means the device can accept an analog signal and then digitize it. It converts sound into information that a computer can manipulate.

Analog signals are continuous waves that vary in frequency and amplitude. An analog audio signal's frequency corresponds to the sound's pitch. The wave's amplitude represents the sound's volume. Digital signals aren't continuous. Instead, a digital signal is a series of snapshots called samples. The number of times a computer takes a snapshot of an analog signal per second is the sampling rate. Higher sampling rates translate into smoother, more natural sound.

©2008 HowStuffWorks
An analog sound wave is continuous.

Not all audio interfaces are also ADCs. Some audio engineers might prefer to use a dedicated ADC, then run the signal coming from the ADC through the audio interface and into the DAW. Either way, the audio interface carries the signal to the DAW. Audio engineers use the DAW to manipulate individual channels and mix the sound into a final track.

The Rest of the Gear

Audio experts like eSessions.com CEO Gina Fant-Saez suggest audio engineers purchase an external hard drive to augment their DAWs. That's because computer hard drives tend to record more slowly than external hard drives. To record audio reliably, you need a hard drive that can spin at faster speeds . Other hardware an audio engineer needs to complete a portable studio includes:

• Headphones
• Microphones
• Speakers
• Cables

The DAW might be the most important hardware component in a portable studio, but it's useless without the right software. Keep reading to learn about the applications audio engineers use to produce music.

Portable Audio Studio Software

Even a powerful DAW is useless without the right software. There are several music studio software packages on the market. Some provide audio engineers with a full suite of functions ranging from mixing and recording to adding effects like echo and reverb. They also range in price -- some are several hundred dollars and others are available free of charge. Most of these software packages provide the same basic set of functions. These include equalizing, editing and mixing. Let's look at each of these in turn.

The Pro Tools suite of software simulates many of the functions of a traditional recording studio.

In audio production, equalizing refers to tweaking the frequency levels on an audio signal. A good software package should allow engineers to do this to individual input channels as well as the overall mix. The software includes an interface known as an equalizer. Equalizers divide frequencies into segments called bands and usually range from 20 hertz (Hz) to 20 kilohertz (kHz), the range of human hearing. By tweaking the intensity levels for the frequency range of an audio signal, an engineer can emphasize or deemphasize certain pitches.

Methods for editing and mixing tracks vary from one software package to another. In general, most packages let you manipulate sections of a track or mix together multiple recordings to create the best final edit. Many packages allow you to cut, copy and paste sections of a track into a new format. Think your chorus should come in a bit earlier? No problem. Use the software's interface to shift it up a few measures.

Editing and mixing can also give engineers other options, such as adjusting the volume of particular channels or sections of the track, fading sound in or out or shifting sound so that it pans from one set of speakers to another.

Sequencers

In music, a sequencer is a device or software application designed to manipulate computer-generated audio. A sequencer makes it possible to mix signals from analog equipment with computer-generated sounds. Many audio engineering software packages include a sequencer application.

One important task audio engineering software handles is working with MIDI data. MIDI stands for Musical Instrument Digital Interface, and is the standard by which computers, electronic musical instruments and other digital devices share musical information. MIDI isn't a music file -- it's a series of digital instructions that tell digital devices how to create a specific sound. Most audio engineering software can edit and mix MIDI data with other recorded audio formats.

How to Set up a Portable Audio Studio

Let's imagine that we have the opportunity to put together a robust portable audio studio. Which equipment do we choose? Which software packages are good choices? How much is it going to cost?

Assuming we aren't going to try and retrofit a current computer system, we'll have to start from scratch. Right from the start we have a choice: PC or Mac? There are several software applications available for both kinds of computers. There are PC and Mac laptops that have the horsepower we need to run an audio studio. The choice usually comes down to personal preference. Some people think that the best choice for people with little computer experience is the Mac, which as a reputation for being user friendly. Let's go with that -- we'll choose a MacBook Pro as our digital audio workstation.

MacBook laptop computers are a popular choice for audio production beginners.

To supplement the computer, we'll need an external hard drive. This is where we'll store recorded audio. By porting storage to an external drive, we free up the computer's resources to handle all the applications we'll be using when producing music. Audio files can be very large, so it's important to choose a hard drive with a lot of space. For example, we could choose the G-Tech G-Drive Q, which has 500 gigabytes worth of storage.

What about the software? We could go with a free software package like Audacity, but that means giving up on some features. For example, as of this writing, Audacity can't edit or mix MIDI data. We could use GarageBand, a popular Mac audio sequencer and audio processor. But compared with other software packages, it just doesn't offer a lot of features. If we want a really robust studio, we'll need something like Pro Tools from Digidesign. Applications like Pro Tools give engineers more control and options when working with sound files.

Once we settle on the software, it's time to think about audio interfaces. Not all audio interfaces are compatible with every software package. That's why we chose our software package first. So the first step in choosing an audio interface device is to make sure it will work with our DAW's software. Let's assume we're using Pro Tools and need a device with at least two analog inputs. Digidesign offers the Mbox 2, which not only has this capability but also comes with a copy of Pro Tools software.

The Mbox 2 is an audio interface that you can connect to a PC or Mac.

On top of this, we'll need to invest in cables, microphones, headphones and speakers. If we want to produce music using the MIDI standard, we'll probably also need to buy a MIDI keyboard controller. While it's important not to skimp on these items if we want high quality sound, we won't necessarily have to break the bank either. Let's assume we pick reliable but affordable hardware.

The cost for the studio would break down like this:

• DAW: our Macbook Pro would cost around $2,500
• Hard drive: the G-Tech drive retails for $230
• Software and audio interface: The Mbox 2 retails for $495 and comes with a copy of Pro Tools software
• Other hardware: Reliable cables, headphones, speakers and a keyboard would cost about $800

The total cost for this studio is $4,025. While that's a healthy chunk of change, it's much less expensive than a traditional recording studio. We could always cut corners and choose more moderately-priced equipment and software, but it's true that you get what you pay for. If money is no object, we could spare no expense and buy the best equipment available. Then you'd really see a hefty bill.

Noise-canceling Headphones

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Bose was the first company to introduce noise-canceling headphones.

One man's noise is another man's music, but no matter what your taste, ambient noise is the enemy. Luckily, there's a piece of audio equipment designed especially to maximize your listening experience, keeping ambient noise out without sacrificing your music's sound quality. That piece of equipment is the headphone, and in this article, we're going to look at how headphones, especially noise-canceling headphones, work.

On a 1978 flight to Europe, Amar Bose, the founder of Bose Corporation, put on a pair of airline-supplied headphones, only to find that the roar of the jet engines prevented him from enjoying the audio.He started making calculations right there on the plane to see if it was possible to use the headphones themselves as a noise-reducing agent. Bose introduced the first noise-canceling headphones a decade later.

­ In order to understand headphones, you must first understand sound waves. You can check out How Speakers Work for some information, but we're also going to provide a brief introduction here.

When most people think of waves, they think of water waves, like you'd seen in an ocean or lake. A shallow water wave is an example of a transverse wave, which causes a disturbance in a medium perpendicular to the direction of the advancing wave. You can see this relationship in the illustration below. The illustration also shows how waves form crests and troughs. The distance between any two crests (or any two troughs) is the wavelength, while the height of a crest (or the depth of a trough) is the amplitude. Frequency refers to the number of crests or troughs that pass a fixed point per second.

Sound waves have many of the same characteristics as water waves, but they are longitudinal waves, created by a mechanical vibration in a medium that produces a series of compressions and rarefactions in a medium. When you pluck a guitar string, for instance, it begins to vibrate. The vibrating string first pushes against air molecules (the medium), then pulls away. This results in an area where all of the air molecules are pressed together and, right beside it, an area where air molecules are spread far apart. As these compressions and rarefactions move from one point to another, they form a longitudinal wave, with the disturbance in the medium moving parallel to the direction of the wave itself.

Longitudinal waves have the same basic characteristics as transverse waves. A compression corresponds to a crest, and a rarefaction corresponds to a trough. The distance between two compressions, then, is the wavelength, while the amount the medium compressed is the amplitude. Frequency refers to the number of compressions that pass a fixed point per second.

­

­For sound waves, amplitude determines the intensity, or loudness, of the sound. Frequency determines the pitch, with higher frequencies producing higher pitch notes and lower frequencies producing lower pitch notes. The brain is able to interpret these characteristics of sound, but before that can happen, the sound waves must be detected by a sense organ. That, of course, is the ear's job. To learn more about how the ear detects and interprets sound, check out How Hearing Works.

Electrostatic and Dynamic Transducers

Music versus Noise As the introduction to this article suggests, differentiating music and noise can be a subjective matter. But scientists make a clear distinction. Music is sound with a reproducible, distinct waveform. Noise refers to random and unpredictable waveforms. And white noise is the most complex type of noise because it contains many different frequencies, all possessing equal intensity.

To hear what's recorded on a record, cassette, CD, DVD or MP3 player, data stored on the medium must be converted into sound waves. This requires that the stored information be turned into an electrical signal, which then must pass through a transducer to convert the transverse electrical wave into a longitudinal sound wave that the ear can interpret. Speakers play the role of transducers in audio systems. They can be located far away from the listener's ear, however.

Headphones were developed specifically to solve this problem. Headphones are essentially speakers held over the ear by a band or wire worn on the head. They are categorized by the type of transducer technology use and by their construction. Let's look first at electrostatic headphones.

Electrostatic Headphones
Electrostatic headphones take advantage of a phenomenon that most people know as static electricity. When an object becomes charged, it either gains or loses electrons. An object that gains electrons is negatively charged; an object that loses electrons is positively charged. Objects with like charge experience repulsive forces, while oppositely-charged object experience attraction. These forces are known as electrostatic forces.

To create these forces in electrostatic headphones, a thin diaphragm -- a flexible sheet made of paper, plastic or metal -- is suspended between two metal grids or electrodes. When an audio signal is applied, varying attractions are created along the grids. This pushes part of the diaphragm toward one grid and pulls part toward the opposing grid. The resulting vibrations in the diaphragm produce the sound waves that are eventually detected by the ear.

Dynamic Headphones
Electrodynamic (or dynamic, for short) headphones are made of three functional parts -- a voice coil, a permanent magnet and a cone-like diaphragm. The narrow end of the cone is attached to the voice coil and actually generates the sound waves. It does this by vibrating rapidly in response to the vibrating voice coil, much the same way the three bones of the ear vibrate in response to the movement of the eardrum.

The vibration of the voice coil is made possible by two fundamental properties of magnetism:

• Identical magnetic poles repel each other, while opposite poles attract
• Electric current flowing through a coil of wire produces a magnetic field, with the direction of current flow determining the polarity of the magnetic field

When a voice coil is placed within the unchanging magnetic field of a permanent magnet, these two properties are realized. Switching the electrical signal that is pumped into the coil causes the North and South poles to switch back and forth very rapidly. As the North and South poles of the voice coil's magnetic field switch, they are attracted and then repelled as they interact with the permanent magnet. Because the permanent magnet is fixed and the voice coil isn't, the latter vibrates and transmits these vibrations to the diaphragm.

Headphone Styles

Dynamic headphones are the most common type of headphone, so let's take a closer look at the three basic earpiece designs.

Supra-aural headphones, also known as on-ear, open-back or open-air headphones, sit lightly on or over the ear. The ear cups are generally softly padded and rotate freely to enhance fit and reduce pressure points. Because they sit on the ear, on-ear headphones leak sound into the external environment and allow ambient noise in.

Supra-aural headphones

Circumaural headphones

Circumaural headphones, also known as around-ear or closed-back headphones, completely enclose the listener's ears. Because they form an airtight seal, they block out external noise without leaking sound to the outside. This improves sound quality, but circumaural headphones tend to be heavier and less comfortable.

In-ear headphones come in two styles: ear buds and canal headphones. Ear buds are worn in the opening of the ear, while canal headphones are seated in the canal itself, forming an airtight seal. Sound quality tends to be excellent with in-ear headphones, although this is dependent on how well they fit in the listener's ear. For this reason, canal headphones, which fit tightly in the ear like earplugs, are often preferred by musicians or others wanting superior sound quality.

In-ear, canal-style headphones are used often by musicians and others desiring superior sound quality.

Noise-canceling Headphones

Bose was the first company to introduce noise-canceling headphones.

Unfortunately for music lovers, many types of ambient sounds can interfere with or even block the sounds coming through their headphones. If you have ever tried to listen to a CD or MP3 player on a plane, then you know the problem well: The roar of the engines makes it difficult to hear what's being piped through the speakers -- even when those speakers are situated in or on your ear. Fortunately, noise-canceling headphones can provide a more enjoyable listening experience.

Noise-canceling headphones come in either active or passive types. Technically speaking, any type of headphone can provide some passive noise reduction. That's because the materials of the headphones themselves block out some sound waves, especially those at higher frequencies. The best passive noise-canceling headphones, however, are circum-aural types that are specially constructed to maximize noise-filtering properties. That means they are packed with layers of high-density foam or other sound-absorbing material, which makes them heavier than normal headphones. The tradeoff of all that extra weight is a reduction in noise of about 15 to 20 decibels (dB). But considering jet engines create 75 to 80 dB of noise inside the aircraft cabin, passive models have some serious limitations. That's where active noise-canceling headphones come in.

Decibel Defined A decibel (dB) is a measure of sound intensity. The dB scale is logarithmic, meaning that a change of 10 dB represents a tenfold change in loudness. So, a sound measuring 30 dB is 10 times louder than a sound measuring 20 dB.

Active noise-canceling headphones can do everything that passive ones can do -- their very structure creates a barrier that blocks high-frequency sound waves. They also add an extra level of noise reduction by actively erasing lower-frequency sound waves. How do noise-canceling headphones accomplish this? They actually create their own sound waves that mimic the incoming noise in every respect except one: the headphone's sound waves are 180 degrees out of phase with the intruding waves.

If you look at the illustration below, you can see how this works. Notice that the two waves -- the one coming from the noise-canceling headphone and the one associated with the ambient noise -- have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out, a phenomenon known as destructive interference. The result: the listener can focus on the sounds he wants to hear.

Of course, several components are required to achieve this effect:

• Microphone - A microphone placed inside the ear cup "listens" to external sounds that cannot be blocked passively.
• Noise-canceling circuitry - Electronics, also placed in the ear cup, sense the input from the microphone and generate a "fingerprint" of the noise, noting the frequency and amplitude of the incoming wave. Then they create a new wave that is 180 degrees out of phase with the waves associated with the noise.
• Speaker - The "anti-sound" created by the noise-canceling circuitry is fed into the headphones' speakers along with the normal audio; the anti-sound erases the noise by destructive interference, but does not affect the desired sound waves in the normal audio.
• Battery - The term "active" refers to the fact that energy must be added to the system to produce the noise-canceling effect. The source of that energy is a rechargeable battery.

Using these components, noise-canceling headphones are able to provide an additional reduction in noise of 20 decibels. That means about 70 percent of ambient noise is effectively blocked, making noise-canceling headphones ideal for airline and train travel, open office environments or any other location with a high level of background noise.

While noise-canceling headphones do a good job distinguishing between the audio a wearer wants to hear and the background noise he or she wants to keep out, some people say that they compromise sound quality by muffling sounds. Users can also experience a change in air pressure, although ports built into the ear cup are meant to vent air trapped behind the speakers.

In spite of these tradeoffs, many people would never go back to normal audio headphones. That's because noise-canceling headphones do more than reduce noise. They also help alleviate fatigue when traveling, which can result from exposure to low-frequency noise for an extended period of time. You can even use noise-canceling headphones if you don't want to listen to another audio source but do want to cancel out background noise. And a little bit of quiet can be music to anyone's ears.

Headphone Hats

A headphone hat will handle a bad hair day and keep you jamming along to your favorite playlist.

These days, many of us don't go anywhere without several different portable pieces of technology in tow. Seriously -- what would we do without our cell phones? How would we call, text, e-mail, Twitter, search the Internet and take photos while we're out grocery shopping? And what about that portable DVD player? It's a lifesaver on long car and plane rides. Our laptops come with us everywhere and have replaced notepads and pens on college campuses around the world. And then, there are all the options we have for music. Walk down any city street and it's more than likely the majority of passers-by will be walking to the beat of their favorite tunes.

But what can an avid music lover do when the winter winds bring frostbite to uncovered ears and the need to bundle up takes precedent to jamming along with your latest play list? Try sorting through the many options available in the headphone hat market.

Headphone hats are exactly what they sound like -- hats with attachable headphones. This way, you can keep your music turned up and keep your head protected from the harsh elements of winter. In fact, these hats aren't meant just for warmth. For a few years, baseball style caps with radio hook-ups have been available for your listening pleasure. Long before the days of MP3 players, headphone hats were available for tape players, portable CD sets and more.

Try looking around online to read about the many options you have. While this seems like a sporty product, you'd be surprised by the wide array of manufacturers. Big box stores can offer you great deals and your favorite clothing store at the mall may have a variety in interesting or stylish patterns. Expect to pay anywhere from $10 for a basic hat and headphone pairing, up to about $200 for the most technologically advanced hat you can find.

Mechanics of Headphone Hats

There's nothing too complicated about the engineering of a headphone hat. The hat can come in baseball styles for regular wear and warmer styles for winter weather. Like a normal set of headphones, there will be two speakers either connected across the top of your head by some sort of band, or secured to the sides of the hat. The speakers are connected by a cable that leads to a universal plug. This plug should fit into most headphone jacks, so you can use your hat with your MP3 player, your cell phone, your computer and so on.

Most styles allow you the convenience of being able to remove the headphones from the hat. This way, you can throw your hat in the washing machine, and you'll have a spare pair of headphones if you need them. Because of this ease, if you lose the headphones, you may be able to replace them with a pair similar in size and design.

Headphone Earmuffs

Now you can stay warm and keep the tunes flowing by getting yourself a pair of headphone earmuffs.

That four-mile jog is so much harder in the winter. The single digits on the thermometer are less than motivational. The one thing that usually helps pump you up, your MP3 player, is still carefully tucked in your room because the thought of those ear bud headphones that feel like ice against your ears is too much to handle on this cold morning. If only you didn't have to choose between your ear bud headphones and your earmuffs.

Well, you're in luck -- now you can stay warm and keep the tunes flowing by getting yourself a pair of headphone earmuffs.

As MP3 players and other portable music gadgets have become practically ubiquitous, it has become necessary to make them as usable as possible, no matter what the temperature is. So, the ever-expanding need for multipurpose gear has created a new branch in the headphone industry. Headphone earmuffs are exactly what you think they are -- headphones inside a pair of earmuffs.

­With everyone from the big box chains to outdoor stores and fashion shops selling the product, you should be able to find a pair that fits your style and budget. They come in a variety of styles and colors and range in price from $10 for a basic pair up to around $200 for a top of the line model. Most of the time, you can expect the average earmuff headphone set to run about $30. Try using the Internet in your search for the best deals and customer reviews.

Mechanics of Headphone Earmuffs

Paving the Way Where would we be today without the innovative thinking behind the Sony Walkman? July 1, 1979 marked the birth of a new way of enjoying music when Sony introduced one of its most famous products. Although it was originally called the "Discman," this musical breakthrough soon became known as the Walkman. Before its production, cars and home stereos were your only options, so the Walkman made music portable for the first time. These days, iPods and other MP3 players have basically made the groundbreaking Walkman obsolete, but who knows if we would have stumbled upon this technology without the foundation Sony laid .

It shouldn't be too hard to imagine headphone earmuffs, after all, just imagine a pair of old-school style headphones -- the kind many club DJs sport. If you can't conjure an image, think of Oreo-sized pads covering two small speakers, attached by a thin, adjustable metal strip -- and it all fits on your head like a pair of earmuffs. Since earmuffs are shaped quite similarly, it's not that far fetched that the two items could be fused into one convenient gadget.

The mechanics involved are about as simple as you would expect. You start with a standard headphone set up. There are two ear cups, each containing a speaker, a headband, a wire connecting the two speaker ear cups and a universal plug that will fit into a variety of different technological accessories .

The headphones are covered in a warm, soft fabric, as if they have their own winter jacket. Sometimes a thin layer of fabric is placed over the speakers, and other times the earmuffs just form a tube around the speakers to protect your ears from the cold. Like most of the earmuffs you've come across, they're usually collapsible and just like the headphones you've used, they're adjustable.

5 Types of Microphones

microphones

Sound is an amazing thing. All of the different sounds that we hear are caused by minute pressure differences in the air around us. What's amazing about it is that the air transmits those pressure changes so well, and so accurately, over relatively long distances.

If you have read the HowStuffWorks article How CDs Work, you learned about the very first microphone. It was a metal diaphragm attached to a needle, and this needle scratched a pattern onto a piece of metal foil. The pressure differences in the air that occurred when you spoke toward the diaphragm moved the diaphragm, which moved the needle, which was recorded on the foil. When you later ran the needle back over the foil, the vibrations scratched on the foil would then move the diaphragm and recreate the sound. The fact that this purely mechanical system works shows how much energy the vibrations in the air can have!

All modern microphones are trying to accomplish the same thing as the original, but do it electronically rather than mechanically. A microphone wants to take varying pressure waves in the air and convert them into varying electrical signals. There are five different technologies commonly used to accomplish this conversion.

1: Carbon Microphones

The oldest and simplest microphone uses carbon dust. This is the technology used in the first telephones and is still used in some telephones today. The carbon dust has a thin metal or plastic diaphragm on one side. As sound waves hit the diaphragm, they compress the carbon dust, which changes its resistance. By running a current through the carbon, the changing resistance changes the amount of current that flows

2: Dynamic Microphones

A dynamic microphone takes advantage of electromagnet effects. When a magnet moves past a wire (or coil of wire), the magnet induces current to flow in the wire. In a dynamic microphone, the diaphragm moves either a magnet or a coil when sound waves hit the diaphragm, and the movement creates a small current.

3: Ribbon Microphones

In a ribbon microphone, a thin ribbon is suspended in a magnetic field. Sound waves move the ribbon which changes the current flowing through it.

4: Condensor Microphones

A condenser microphone is essentially a capacitor, with one plate of the capacitor moving in response to sound waves. The movement changes the capacitance of the capacitor, and these changes are amplified to create a measurable signal. Condenser microphones usually need a small battery to provide a voltage across the capacitor.

5: Crystal Microphones

Certain crystals change their electrical properties as they change shape (see How Quartz Watches Work for one example of this phenomenon). By attaching a diaphragm to a crystal, the crystal will create a signal when sound waves hit the diaphragm.

As you can see, just about every technology imaginable has been harnessed to convert sound waves into electrical signals. The one thing they all have in common is the diaphragm, which collects the sound waves and creates movement in whatever technology is being used to create the signal.

High-Tech Gadgets

1. UPS Bar Codes
2. RFID
3. Psychotechnology
4. Facial Recognition System
5. Energy-efficient Electronics
6. Electronic Ink
7. Anti-shoplifting Devices
   

UPC Bar Codes

UPC codes were first used in grocery stores.

If you go look in your refrigerator or pantry right now, you will find that just about every package you see has a UPC bar code printed on it. In fact, nearly every item that you purchase from a grocery store, department store and mass merchandiser has a UPC bar code on it somewhere.

Have you ever wondered where these codes come from and what they mean? In this article, we will solve this mystery so that you can decode any UPC code you come across.

"UPC" stands for Universal Product Code. UPC bar codes were originally created to help grocery stores speed up the checkout process and keep better track of inventory, but the system quickly spread to all other retail products because it was so successful.

UPCs originate with a company called the Uniform Code Council (UCC). A manufacturer applies to the UCC for permission to enter the UPC system. The manufacturer pays an annual fee for the privilege. In return, the UCC issues the manufacturer a six-digit manufacturer identification number and provides guidelines on how to use it. You can see the manufacturer identification number in any standard 12-digit UPC code. The UPC symbol has two parts:

• The machine-readable bar code
• The human-readable 12-digit UPC number

The manufacturer identification number is the first six digits of the UPC number -- 639382 in the image above. The next five digits -- 00039 -- are the item number. A person employed by the manufacturer, called the UPC coordinator, is responsible for assigning item numbers to products, making sure the same code is not used on more than one product, retiring codes as products are removed from the product line, etc.

In general, every item the manufacturer sells, as well as every size package and every repackaging of the item, needs a different item code. So a 12-ounce can of Coke needs a different item number than a 16-ounce bottle of Coke, as does a 6-pack of 12-ounce cans, a 12-pack, a 24-can case, and so on. It is the job of the UPC coordinator to keep all of these numbers straight!

The last digit of the UPC code is called a check digit. This digit lets the scanner determine if it scanned the number correctly or not. Here is how the check digit is calculated for the other 11 digits, using the code 63938200039 from "The Teenager's Guide to the Real World" example shown above:

1. Add together the value of all of the digits in odd positions (digits 1, 3, 5, 7, 9 and 11).
   6 + 9 + 8 + 0 + 0 + 9 = 32

2. Multiply that number by 3.
   32 * 3 = 96

3. Add together the value of all of the digits in even positions (digits 2, 4, 6, 8 and 10).
   3 + 3 + 2 + 0 + 3 = 11

4. Add this sum to the value in step 2.
   96 + 11 = 107

5. Take the number in Step 4. To create the check digit, determine the number that, when added to the number in step 4, is a multiple of 10.
   107 + 3 = 110

   The check digit is therefore 3.

Each time the scanner scans an item, it performs this calculation. If the check digit it calculates is different from the check digit it reads, the scanner knows that something went wrong and the item needs to be rescanned.­

How is the Price Determined?

As you can see, there is no price information encoded in a bar code. When the scanner at the checkout line scans a product, the cash register sends the UPC number to the store's central POS (point of sale) computer to look up the UPC number. The central computer sends back the actual price of the item at that moment.

This approach allows the store to change the price whenever it wants, for example to reflect sale prices. If the price were encoded in the bar code, prices could never change. On the other hand, not encoding a fixed price gives the store an easy way to rip off customers. When you hear about "scanner fraud" in the news, that is what the newsperson is talking about. It is incredibly easy for a store to mistakenly or purposefully overprice an item.

One thing you will notice if you start looking at UPC codes in detail is that the big manufactures have manufacturer IDs with lots of zeros in them. Here are a few:

• Post - 043000
• General Mills - 016000
• Del Monte - 024000
• Quaker Oats - 030000

Here is the bar code from a 3-liter bottle of Diet Coke:

You can see that Coke's manufacturer ID is 049000. However, if you look at can of Coke or most 2-liter bottles, you will find that the UPC code is much shorter -- only eight digits total. Here's the bar code from a 2-liter bottle of Sprite:

These short bar codes are called zero-suppressed numbers. There's a set of rules around forming zero-suppressed numbers from full numbers, but the basic idea is to leave out a set of four digits, all zeros. In the case of the Sprite UPC code, the 049 at the beginning is the first three digits of Coke's 049000 manufacturer ID. The 551 is the item number for this bottle of Sprite, shortened from 00551. The zero in the second-to-last digit is the fourth digit from Coke's manufacturer ID. The final digit is the normal check digit. The main reason for having zero-suppressed numbers is to create smaller bar codes for small product packages like 12-ounce cans.

The first digit of the manufacturer's identification number is special. It is called the number system character. The following table shows you what different number system characters mean:

0	Standard UPC number (must have a zero to do zero-suppressed numbers)
1	Reserved
2	Random-weight items (fruits, vegetables, meats, etc.)
3	Pharmaceuticals
4	In-store marking for retailers (A store can set up its own codes, but no other store will understand them.)
5	Coupons
6	Standard UPC number
7	Standard UPC number
8	Reserved
9	Reserved

Here is an example of a pharmaceutical bar code (number system character 3), this one from a 4-ounce bottle of Selsun Blue dandruff shampoo:

Here is an example of in-store marking (number system character 4), in this case from a $10 Toys R Us gift certificate:

Since Toys R Us is the only store that will ever use this bar code -- it's the only place where the gift certificate can be redeemed -- Toys R Us made up its own UPC code for the gift certificate and used number system 4 so it could do that.

What is a Coupon Code?

The coupon code is interesting (number system character 5). If you have ever wondered how the scanner can read a coupon and reject it if you haven't bought the product, here's your explanation. Here is the UPC code from a box of Post Honey Nut Shredded Wheat:

Here is the coupon for the same product:

You can see that the coupon's bar code starts with a 5 to indicate that it is a coupon. The 43000 is Post's manufacturer ID. The next three digits (186) are called the family code. The next two digits (70) are a value code. The final digit is the normal check digit.

The family code and value code are set up arbitrarily by the UPC coordinator for the manufacturer. It must be done that way because a coupon will often be usable for a whole family of products. For example, a coupon might be good for four different kinds of soap made by the same manufacturer. In the same way, the value code represents the value of the coupon arbitrarily. The manufacturer sends the retailer the data that tells the retailer's computer exactly which products fit the family code, and exactly how much to take off. When the coupon is scanned, the POS computer:

1. Decodes the family code
2. Checks to make sure the customer purchased an item from the family
3. Decodes the value code
4. Sends the discount back to the cash register

Can I Decode the Bars?

So let's say you would like to decode the actual bars in the bar code and map them to numbers. This is something that will make you cross-eyed, but it can be done.

First of all, look at any 12-digit bar code. It is made up of black bars and white spaces between the bars. Assume that the thinnest bar or space that you see (for example, the first bar on the left) can be called "one unit wide." The bars and spaces can therefore be seen to have proportional widths of one, two, three or four units. If you look at any bar code you can see examples of these four widths.

The start of any bar code is "1-1-1." That is, starting at the left you find a one-unit-wide black bar followed by a one-unit-wide white space followed by a one-unit-wide black bar (bar-space-bar). Following the start code, the digits are encoded like this:

     0 = 3-2-1-1
    1 = 2-2-2-1
    2 = 2-1-2-2
    3 = 1-4-1-1
    4 = 1-1-3-2
    5 = 1-2-3-1
    6 = 1-1-1-4
    7 = 1-3-1-2
    8 = 1-2-1-3
    9 = 3-1-1-2

(Something to notice: All of these encodings seem to add up to 7.)

So let's take this barcode as an example:

The code embedded in the bars is 043000181706:

• The bar code starts with the standard start code of 1-1-1 (bar-space-bar).
• The zero is 3-2-1-1 (space-bar-space-bar).
• The four is 1-1-3-2 (space-bar-space-bar).
• The three is 1-4-1-1 (space-bar-space-bar).
• The next three zeros are 3-2-1-1 (space-bar-space-bar).
• In the middle there is a standard 1-1-1-1-1 (space-bar-space-bar-space), which is important because it means the numbers on the right are optically inverted!
• The one is 2-2-2-1 (bar-space-bar-space).
• The eight is 1-2-1-3 (bar-space-bar-space).
• The one is 2-2-2-1 (bar-space-bar-space).
• The seven is 1-3-1-2 (bar-space-bar-space).
• The zero is 3-2-1-1 (bar-space-bar-space).
• The six is 1-1-1-4 (bar-space-bar-space).
• The stop character is a 1-1-1 (bar-space-bar).

Have fun decoding those 12-digit bar codes!