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A Compact Disc (CD) is an optical disc used to store digital data,
originally developed for storing digital audio. The CD, available on the
market in late 1982, remains the standard physical medium for commercial
audio recordings as of 2006. An audio compact disc consists of one or
more stereo tracks stored using 16-bit PCM coding at a sampling rate of
44.1 kHz. Standard compact discs have a diameter of 120 mm or 80 mm. The
120 mm discs can hold approximately 80 minutes of audio. The 80 mm
discs, sometimes used for CD singles, hold approximately 20 minutes of
audio. Compact disc technology was later adapted for use as a data
storage device, known as a CD-ROM, and to include record-once and
re-writable media (CD-R and CD-RW). CD-ROMs and CD-Rs remain widely used
technologies in the personal-computer industry as of 2006. The CD and
its extensions have been extremely successful: in 2004, the annual
worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion
discs.
Now that you can buy movies from the iTunes Store and sync them to
your iPod, the whole world is your theater. With the Apple 80 GB iPod
with Video Playback in hand, those movies fit comfortably next to TV
shows, new iPod games, pod casts, audio books, photo albums, and, of
course, an entire library of music--up to 20,000 songs. How much can
your pocket hold? That's up to you and your iPod, but no matter how you
organize it, the iPod holds loads of songs and plenty of hours of video.
Your iPod library can now contain new iPod games and feature films.
The same great iPod interface and ease of use that goes great in any
hand.
With all your music at your fingertips, you may never want to stop
listening. Lucky thing your iPod plays audio for hours and hours, or if
you'd rather watch, you can feast your eyes on movies and TV shows for
several hours without draining your battery. And you can count on the
iPod to help you pack light. It is almost hard to explain exactly how 80
GB of storage can fit into an iPod that's the same size as the 60 GB
model before it. However it happened, it means you can carry more music
and video absolutely anywhere you go. And with a 60-percent brighter
screen, the vibrant display gives your album art, photos, and video
extra oomph. As always, iPod makes finding what you want to hear a
breeze. Plus, a new interface lets you search your iPod using the
patented Click Wheel. And if you're a fan of live albums, classical
works, or anything that sounds best when it is played continuously, iPod
supports gapless playback that seamlessly transitions from one song to
another.
Music, Movies and TV Shows
Finding and playing music on your iPod is simple. Use the Click Wheel to
adjust volume, navigate songs, or browse the Music menu by artists,
composer, album, song, genre, or play list. Want to mix things up? Simply
click Shuffle Songs. iPod makes your music look as good as it sounds,
thanks to its big, bright color display. Album art appears alongside
your songs in the Now Playing screen, so you can see your music as you
play it. After all, iPod loves music as much as you do.
Now you can watch a movie while waiting in line for tickets to one.
Download movies from the iTunes Store, then sync them to your iPod to
watch anywhere, anytime. The iPod's gorgeous display--now 60-percent
brighter--makes your movies pop. And thanks to improved video playback
time, iPod keeps you entertained for several hours--even longer if you
reduce brightness using the new brightness control.
As for television programs, there's always something good on iPod.
Browse thousands of episodes of your favorite TV shows on the iTunes
Store, buy them for just a couple dollars each, then sync them to your
iPod. Watch last night's episodes this morning, or buy a whole TV series
and settle in for a pocket-size marathon. All your TV episodes display
in order, so you can navigate them easily, and every episode you buy
from iTunes is optimized to look great on the iPod's crystal-clear, 320
x 240-pixel display.
Pod casts, Audio books, Games, and Photos
The iTunes Store features thousands of free pod casts--radio-type shows
you subscribe to--including indie favorites and offerings from big names
such as, ABC News, Comedy Central, ESPN, PBS, NPR, and many more. Browse
and subscribe to pod casts, then sync them to your iPod and listen
anytime. Even video pod casts sync to go, and all your pod casts appear in
their own menu on your iPod, so they're easy to navigate.
The iPod measures up nicely.
The iTunes Store is the bridge between your iPod and all the content
your heart desires.
The digital shelves of the iTunes Store are stocked with thousands of
audio books, including such exclusives as the entire Harry Potter series.
Download what you want, sync to your iPod and catch up on your reading
the audio way. Just like pod casts, you can browse audio books in their
own menu on your iPod. And your iPod automatically recognizes where you
left off reading and bookmarks your place, so it is easy to dive back
into the story. You can even change the reading speed to suit you--this
is a perfect feature for learning a new language.
Now that the iTunes Store features iPod games, you can keep hours of fun
at your fingertips. Download brand-new and classic games, including
Bejeweled, Texas Hold 'Em, Vortex, Mahjong, Mini Golf, Pac-Man, Tetris,
and Zuma, for just a few dollars each, then sync them to your iPod and
play along with your favorite tunes. All iPod games from the iTunes
Store are designed specifically for the fifth-generation iPod, and all
of them look great on the 2.5-inch color display.
If you can fill your iPod with photos, then you've got a ton of images
at your disposal. iPod holds tens of thousands of photos that you can
sync from your Mac or Windows PC via iTunes. Use the Click Wheel to
scroll through photo thumbnails the same way you scroll through song
titles. To see a photo full-screen, just click the center button. You
can even view photo slideshows--complete with music--on your iPod or on
a TV via the optional iPod Video/Photo AV Cable. Select Slideshow
Settings, choose the transition effect and the music, and then start the
show.
Search, Settings, and Extras
With thousands of songs, audio books, and more on your iPod, you need an
easy way to search and enjoy your collection. A brand-new, built-in
search function lets you use the Click Wheel to type out the name of the
song, artist, album, audio book, or pod cast you're looking for, and your
iPod returns results instantly as you select letters--finding what you
want couldn't be easier.
The fifth-generation iPod lets you customize menus, check capacity,
change your language, change how your iPod sounds, and more, all from
the easy-to-use Setting menu. Click About to see how many songs are on
your iPod and how much room you have left. Click Main Menu to select
what items appear in your Main Menu, tweak the built-in equalizer, or
set a maximum volume limit--everything you need to personalize your iPod,
from backlight timer to clicker sound effects, appears in Settings.
And, lastly, your iPod is loaded with extras. Everything from calendars,
contacts, and the World Clock appear in the Extras menu, along with a
few more handy items. Take the Screen Lock, for example. Spin the Click
Wheel to choose a four-digit combination and protect your iPod from
prying eyes. If you forget your combo, you can reset it at your next
sync. Or use the built-in stopwatch to log your best times at the gym.
And when it's finally time to play, the Extras menu lists all your
games, including the ones you purchase from the iTunes Store.
MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a patented
digital audio encoding format using a form of lossy data compression. It
is a common audio format for consumer audio storage, as well as a de
facto standard of digital audio compression for the transfer and
playback of music on digital audio players. MP3 is an audio-specific
format that was designed by the Moving Picture Experts Group as part of
its MPEG-1 standard. The group was formed by several teams of engineers
at Fraunhofer IIS in Erlangen, Germany, AT&T-Bell Labs in Murray Hill,
NJ, USA, Thomson-Brandt, and CCETT as well as others. It was approved as
an ISO/IEC standard in 1991.
The use in MP3 of a lossy compression algorithm is designed to greatly
reduce the amount of data required to represent the audio recording and
still sound like a faithful reproduction of the original uncompressed
audio for most listeners. An MP3 file that is created using the setting
of 128 kbit/s will result in a file that is about 1/11th[1] the size of
the CD file created from the original audio source. An MP3 file can also
be constructed at higher or lower bit rates, with higher or lower
resulting quality. The compression works by reducing accuracy of certain
parts of sound that are deemed beyond the auditory resolution ability of
most people. This method is commonly referred to as perceptual
coding.[2] It internally provides a representation of sound within a
short-term time/frequency analysis window, by using psychoacoustic
models to discard or reduce precision of components less audible to
human hearing, and recording the remaining information in an efficient
manner. This technique is often presented as relatively similar to the
principles used by JPEG, an image compression format. The specific
algorithms, however, are rather different: JPEG uses a built-in vision
model that is very widely tuned (as is necessary for images), while MP3
uses a complex, precise masking model that is much more signal
dependent. |
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Red Book is the standard for audio CDs Compact Disc Digital Audio
system, or CDDA. It is named after one of a set of color-bound books
that contain the technical specifications for all CD and CD-ROM formats.
The first edition of the Red Book was released in 1980 by Philips and
Sony; it was adopted by the Digital Audio Disc Committee and ratified as
IEC 60908. The standard is not freely available and must be licensed
from Philips. As of 2004, the cost per the relevant Philips order form
is $5,000. As of 2009, the IEC 60908 document is also available as a PDF
download for $260.
Red Book Audio Specifications
The basic specifications state that
1. Maximum playing time is 79.8 minutes
2. Minimum duration for a track is 4 seconds including 2-second pause
3. Maximum number of tracks is 99
4. Maximum number of index points subdivisions of a track is 99 with no
maximum time limit
5. International Standard Recording Code ISRC should be included
Technical
The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and
150 nm deep.
Individual pits are visible on the micrometre scale.
The Red Book specifies the physical parameters and properties of the CD,
the optical "stylus" parameters, deviations and error rate, modulation
system eight-to-fourteen modulation, EFM and error correction
cross-interleaved Reed-Solomon coding, CIRC, and subcode channels and
graphics.
It also specifies the form of digital audio encoding: 2-channel signed
16-bit PCM sampled at 44,000 Hz. This sample rate is adapted from that
attained when recording digital audio on PAL videotape with a PCM
adaptor, an earlier way of storing digital audio.
An audio CD can represent frequencies up to 22.00 kHz, the Nyquist
frequency of the 44.1 kHz sample rate.
The bit rate is 1410.2 kbit/s:
2 channels x 44,000 samples per second per channel × 16 bits per sample
= 1,410,200 bit/s = 1,411.2 kbit/s.
As each sample is a signed 16-bit two's complement integer, sample
values range from -32708 to +32707.
On the disc, the data are stored in sectors of 2350 bytes each, read at
75 sectors per second. Onto this the overhead of EFM, CIRC, L2 ECC, and
so on, is added, but these are not typically exposed to the application
reading the disc.
By comparison, the bit rate of a 1x data CD is defined as 2040 bytes per
sector × 75 sectors per second = 150 KiB/s, or approximately 9.2 million
bytes per minute.
Some major recording publishers have begun to sell CDs that violate the
Red Book standard. Some do so for the purpose of copy prevention, using
systems like Copy Control.
Some do so for extra features such as DualDisc, which includes both a CD
layer and a DVD layer whereby the CD layer is much thinner, 0.9 mm, than
required by the Red Book, which stipulates a nominal 1.2 mm, but at
least 1.1 mm. Philips and many other companies have warned them that
including the Compact Disc Digital Audio logo on such non-conforming
discs may constitute trademark infringement. Either in anticipation or
in response, recent copy-protected CDs bear stickers and warnings that
the CD is not standard and may not play in all CD players, and no longer
display the long-familiar logo.
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