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iPod® Glossary

Ralph Graves is one of Crutchfield's blog editors, and part of the company's social media team. He writes about home audio/video gear, specializing in Apple-related and wireless technologies. Ralph holds a master's degree in music composition, and his works have been released on various labels. He's served as product manager for an independent classical and world music label, produced several recordings, and worked extensively in public broadcasting. Since 1984 he's hosted a weekly classical music program on WTJU, and is also active as a blogger and podcaster.

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Click on a letter below to jump to that section of the glossary.



AAC (Advanced Audio Coding)
A compression format for digital audio. AAC is a newer, more advanced form of compression than the MP3 format. According to some listening tests, AAC files encoded at lower bit rates (like 96 Kbps) sound as good as, or better than, MP3s encoded at higher bit rates (like 128 kbps) despite their notably smaller size.

The current version of the AAC codec was developed as part of the MPEG4 standard. (See our MPEG definition for more on this family of audio/video compression standards.) AAC is the audio format used by Apple in their iTunes® Store. Files may appear on your system with the ".m4a" filename extension.

An accelerometer measures motion and gravitational effects. In an iPod, it's used to detect screen orientation to display a portrait view when the player's held vertically, and a widescreen view when the player's held horizontally. It triggers the shuffle mode in an iPod nano when the player's shaken. The accelerometer in the iPod touch lets you control game play by tilting and tipping the player.

AIFF (Audio Interchange File Format)
An audio format for Macintosh® operating systems commonly used for storing uncompressed, CD-quality sound (similar to WAV files for Windows-based PCs).

Apple Lossless
Apple Lossless Encoding (also known as Apple Lossless, Apple Lossless Audio Codec or ALE) is an audio codec developed by Apple Computer that provides full, uncompressed CD-quality audio in about half the space of the original file.

The term "app" is short for application. Some members of the Apple family of devices, such as the iPhone, iPod Touch, and iPad can be customized with apps purchased from the iTunes Store. An app is usually a small, simple, single-function program, such as a display for weather forecasts, or headline news. Some allow access to online content. Others give the device additional functionality, such as an app that uses the player's accelerometer to turn it into a level. There are currently over 220,000 apps available from the iTunes Store, with more being added daily.

A digital file format for spoken word files purchased from the website. Audible files are available at four compression rates — Audible 1, 2, 3, and 4 — with 4 being the least compressed and 1 being the most compressed. iPods are compatible with files encoded in Audible formats 2 through 4.

Auxiliary input
An input that enables you to connect an iPod (or any other audio device) to a receiver. The input can be either minijack or RCA.

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Bit rate
With audio compression, the average amount of data required to store one second of music (expressed in kilobits per second, or Kbps). Some codecs like MP3, and AAC allow files to be encoded at different bit rates. Generally, as bit rate decreases, so does the sound quality of the resulting file, as well as the amount of memory required to store it.

Brand-name stereo iPod adapters
An adapter that lets you connect your iPod to your brand-name (or aftermarket) car stereo (vs. a factory stereo iPod adapter). The type of adapter you choose depends upon whether your car stereo includes an auxiliary input. Use our iCarStereosm tool to see the adapters that work with your iPod and your car stereo.

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Cassette adapter
This accessory lets you listen to your iPod through the cassette player in your car. It connects to the iPod's headphone output.

Click Wheel
Introduced in 2004, this is the type of control used by iPod nanos and iPod classics (as well as the now discontinued iPod minis). The ingenious Click Wheel incorporates the Menu, Fast-Forward, Rewind, and Play/Pause buttons within the wheel itself, so you can scroll through songs and perform those functions, all from one control.

Cover Flow
Cover Flow is a graphic user interface used for navigation in the iPod touch. The player's touchscreen presents album artwork flowing past in a three-dimensional fashion, as if the albums were swiveling on a rotating rack. Sensors in the touchscreen follow the motion of your finger and go either forward or backwards through the albums accordingly. iTunes has a similar interface that can be operated with your mouse. The iPod classic and iPod nano also have a version of Cover Flow that's operated by the player's Click Wheel.

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A cradle for the iPod that connects to a computer for charging the battery and transferring songs and video. Most docks connect to your computer via USB 2.0.

An iPod dock features a multi-pin plug that goes into the base of your player, identical to the one on your player's provided charging cable. You can use the Dock to simplify any kind of connection: the Dock accepts an AC line and can be used as a stand-alone charger. Many docks let you connect your player to your audio/video system through some combination of composite video, S-video, or component video, and stereo minijack or stereo RCA audio connectors.

[Shop our selection of iPod/iPhone docks.]

Dock connector
The port on an iPod that connects it to a Dock, or to a special cable that allows battery charging and music transfer when connected to a computer.

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Factory stereo iPod adapters
An adapter that lets you connect your iPod to your factory car stereo. Most factory stereo iPod adapters will charge the iPod and allow you to navigate playlists with your car stereo controls (usually including steering wheel controls). Use our iCarStereosm tool to see the adapters that work with your iPod and your car stereo.

Also known as IEEE 1394 or i.LINK®, FireWire is an extremely fast (up to 400 megabits per second), two-way digital connection used between a computer and an iPod. Newer iPods do not offer FireWire connectivity, but some older generation models accept it in addition to USB.

Flash memory
A form of digital storage developed in 1988 for use in personal computers and PC peripherals, flash memory gets its name because sections of memory cells within the microchip are erased in one simultaneous action, or "flash." Today, flash memory is used in portable MP3 players like the iPod shuffle, as well as in handhelds/PDAs, digital cameras, and for storing digital still pictures in digital camcorders. Because it has no moving parts, flash memory is completely immune to skipping when it's used for audio storage.

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A feature of iTunes that creates playlists based on a selected track, generated from music stored in your iTunes library. Genius learns your preferences and how you relate songs by following your listening patterns. It then uses those patterns along with other track information such as artist, genre, etc., to create its playlist.

The more you use iTunes, the more accurately Genius can anticipate your preferences. When you update Genius to the iTunes store, that information is added anonymously to that of everyone else who updated to the iTunes database. This accumulated data allows the Genius feature to make increasingly intelligent recommendations.

This feature is available in the current versions of the iPod nano, iPod touch, iPod classic, and iPhone. Everytime you sync your player, Genius information stored on your device is updated. If you use the Genius button when your player isn't docked, the progam simply creates its playlists from the songs stored on your device.

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Hard drive
A hard drive — just like the one inside your computer, only smaller — is the type of memory used by the iPod classic and iPod touch to store music and data. A larger hard drive means that you can save more music, photos, or information to your iPod. Because it has moving parts, a hard drive theoretically can skip while playing music; however, the iPod's 25-minute skip protection minimizes this.

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Apple's tablet computer. The iPad features a large 9.7 diagonal touchscreen, with a virtual keyboard. The iPod has built-in Wi-Fi and can be used with AT&T's 3G network for Internet browsing. The iPad can store and play videos, music, and games. It also has an accelerometer to change screen orientation and activate Cover Flow. According to Apple, the iPad bridges the gap between a smart phone and a netbook computer.

Apple's mobile phone. The iPhone uses motion-sensing touchscreen with a virtual keyboard. The iPhone has Internet connectivity, and can be customized with a wide variety of apps. Like the iTouch, the iPhone can store and play music and videos. It uses Cover Flow, has a built-in GPS tracker, and a motion-sensing accelerometer allows for control by tilting the device. The current model is known as the iPhone 4.

iPod classic®
A full-sized version of the iPod equipped with a color LCD, now properly known as the "iPod classic." It can play movies and other videos, display photos, as well as play music and games. The current version available is the third generation model (see our handy chart for more information on iPod generations). It is available in black and white and with 160GB of storage capacity.

iPod nano®
Smaller and more colorful than the iPod classic, the iPod nano is a popular choice for on-the-go listening. The current version available is the sixth generation model (see our handy chart for more information on iPod generations). The iPod nano comes in 8GB and 16GB versions and is available in several colors. The iPod nano runs off of flash memory so it's 100% skip-free.

iPod shuffle®
The iPod shuffle is the tiniest iPod available. Like the nano, it features flash memory for skip-free playback on the go. The current version available is the fourth generation model (see our handy chart for more information on iPod generations). The iPod shuffle is available in either silver or black, with 4GB of memory.

iPod touch®
Modeled on Apple's iPhone, the iPod touch shares many of the same features. It uses a motion-sensing touchscreen rather than a Click Wheel, allowing it to have several virtual buttons for various kinds of control. The screen also allows for fast browsing through Cover Flow.

The iPod touch is Wi-Fi enabled, which lets you browse the Internet, check email, download applications from iTunes, and more when you're at a Wi-Fi hot spot or have a Wi-Fi connection. A motion-sensing accelerometer allows for control by tilting the device. The current iPod touch is the fourth generation model (see our handy chart for more information on iPod generations).

Compatible with both Mac and PC, iTunes is the combination jukebox/music download software that Apple includes with the iPod. It allows easy transfer of music, TV shows, movies, podcasts, games, and other content to your iPod from your computer. It also serves as the source for the iTunes Apps Store, which sells applications for the iPhone and iPod touch.

iTunes tagging
A process that lets you select the song you're listening to on an HD Radio™ station and save it for purchasing at a later time. (See our article on HD Radio to learn how digital HD Radio is different from regular AM and FM.)

To do iTunes tagging, you need a docking iPod, an audio/video component with an HD Radio tuner, iPod dock and "Tag" button; and a local radio station broadcasting an HD Radio signal that has enabled tagging.

As you're listening to a station broadcasting a tag-enabled HD Radio signal, press the "Tag" button when you hear a song you like. The component saves the song information (but not the song itself) in its memory. The information automatically transfers to your iPod when you dock it to the component. The next time you sync your iPod to your computer, your tagged selections appear as a list in iTunes, giving you the option of buying them through the iTunes Store. The purchased tracks are then downloaded to your PC's iTunes library, and copied to your iPod.

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MP3 (MPEG-1, Audio Layer 3)
The most popular codec for storing and transferring music. Though it employs a "lossy" compression system which removes frequencies judged to be essentially inaudible, MP3 still manages to deliver near-CD sound quality in a file that's only about a tenth or twelfth the size of a corresponding uncompressed WAV file. When creating an MP3 file, varying amounts of compression can be selected, depending on the desired file size and sound quality. For more info on this topic, see our article on the MP3 format.

One of the most commonly used codecs for storing and transferring video. MPEG-4 compresses audio and video content into manageable file sizes, especially for portable devices such as iPods. MPEG-4 video files usually have an ".mp4" or .m4v" filename extension.

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The QuickTime® video format is Apple's proprietary variant of the MPEG-4 codec. Like MPEG-4, QuickTime compresses and audio and video content for more efficient storage on portable devices, such as iPods. QuickTime players come bundled with iTunes. QuickTime video files usually have a ".qt" or ".mov" filename extension.

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See iTunes tagging

The touchscreen is currently found on the iPod touch. Initially developed for Apple's iPhone, the touchscreen is actually a multi-touch screen. The screen can process several touch points simultaneously to better accurately interpret hand motion and respond accordingly.

Touch Wheel
Used by earlier generations of the iPod, this control is a wheel that lets you scroll through songs. Unlike the later Click Wheel control, the Touch Wheel does not incorporate the Menu, Fast-Forward, Rewind, and Play/Pause buttons.

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USB port
USB (Universal Serial Bus) is a "plug and play" interface between a computer and your iPod (and other devices, including digital cameras, joysticks, keyboards, and printers). The new USB 2.0 standard transmits data at 480 Mbps. That kind of speed makes USB 2.0 suitable for transferring demanding files like full-motion video, etc. Fortunately, all USB 2.0 devices are backwards-compatible with existing USB 1.1 devices.

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WAV (Waveform audio format)
A standard audio format for Windows operating systems, often used for storing high-quality, uncompressed sound. WAV files can contain CD-quality (44.1 KHz/16-bit) audio signals. However, CD-quality WAV files require relatively large amounts of memory — roughly 10 MB per minute of music.

Wi-Fi is a wireless protocol developed to allow various kinds of devices to talk to each other. Cellular phones use this kind of connectivity, as do home wireless computer networks. The iPod touch is also one such Wi-Fi enabled device. Many shops, hotels and other businesses offer "open" Wi-Fi hot spots — places where you can access the Internet through your wireless device without needing a password or special software.

Wired FM modulator
A wired FM modulator can connect the iPod to any car stereo, and requires permanent installation. It offers good sound quality, though it does not allow you to charge the iPod's battery or control playback functions through your car stereo. Use our iCarStereosm tool to see wired FM modulators that work with your iPod.

Wireless FM transmitter
A wireless FM transmitter lets you listen to your iPod through your car's FM radio. It offers acceptable sound quality and typically does not require permanent installation. Use our iCarStereosm tool to see wireless transmitters that work with your iPod.

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