The MP3 standard divides the frequency spectrum into 576 frequency
bands and compresses each band independently. The human ear is
good at hearing mid-range pitch noises, but no so good at high
or low pitched noises. These can be heard - but not well enough
for the details to be accurately distinguished. These bands can
therefore be heavily compressed without any noticeable affect on
overall sound quality using a technique known as perceptual coding.
Where two sounds occur at the same time, MP3 records only the one
that will actually be picked up by the ear. Similarly, a quiet
sound immediately following a loud one can be removed, since this
wouldn't be picked up anyway. Sounds are also compressed in stereo
- if a sound is identical on both stereo channels, it's only stored
once - but it appears on both channels when the MP3 file is decompressed
and played.
Additionally, MP3 adds a modified Discrete Cosine Transform (DCT)
that implements a filter bank, increasing the frequency resolution
18 times higher than that of layer 2. The result in real terms
is that MP3 allows compression of CD-quality audio files by a factor
of 12 with little loss in quality. About one minute's worth of
CD-quality audio can be compressed to about one megabyte of data
- so a typical 4-minute CD track can be stored in a file of between
3.5MB and 5MB. An MP3 file - they use the file extension .mp3 -
can also contain information about the file itself in a tag. The
tag can contain things like the artist's name, a graphic (usually
the CD cover art), a URL for further information, the song's lyrics,
the genre, etc.
In the mid-1990s students at US college campuses began to use
MP3 technology to trade recordings between themselves - and it
quickly became part of everyday campus life. It was only slowly
emerging into the mainstream - until the Recording Industry Association
of America (RIAA) decided to sue Diamond Multimedia over its distribution
of a Korean invention called the Rio in the autumn of 1998. This
Sony Walkman-like device was essentially an MP3 storage device
capable of playing up to an hour of MP3-coded music. The original
suit failed to prevent the Rio coming to market and, following
an appeal, the case was finally thrown out in June of 1999, - the
court finding that the Rio did not qualify as a "digital audio
recording device" and was therefore not subject to the restrictions
of the US 1992 Audio Home Recording Act. What the ill-conceived
lawsuit did succeed in doing was drawing national attention to
MP3 which, almost overnight, metamorphosising it from an underground
movement among Internet-savvy technophiles to a pop culture phenomenon.
Most MP3 files will have been produced from material originating
on an audio CD. This is a two-stage process, the first involving
the conversion of tracks from the CD-DA digital audio format to
WAV format. This step is crucially important, and unavoidable.
There are some programs that can produce an MP3 directly from CD
audio, but they accomplish this by performing an audio extraction
from the CD as the initial step in the process. The task is performed
by specialised programs known as CD-Rippers. The CD-Ripper reads
the tracks of an audio CD digitally and writes them to hard disk
as WAV files. A 4-minute track occupies around 40-50MB in WAV format,
so the conversion of an entire CD requires a large amount of hard
disk space.
The second stage in the process is to convert the .wav files to
.mp3 format. This step also involves the use of specialised software,
and the programs that perform this task are known as MP3 Encoders.
MP3 files can be produced using a variety of compression rates,
allowing users to choose their optimal mix of quantity and quality.
Typically, the following options are available:
"CD quality" - compressed at 12:1 at rates of between
128 Kbit/s at the low end and up to 192 Kbit/s at the high end
" Near-CD quality" - compressed at around 18:1, and
" FM Radio Quality" (Real Audio), be compressed 70:1 at a rate of 64
Kbit/s.
The majority of the MP3 files available on the Internet are encoded at
44kHz and 128 Kbit/s - a bitrate which results in a good quality/size
ratio MP3 file. Encoding at 192 Kbit/s will produce a superquality result
- but at the cost of a considerably larger file size. Tracks recorded
at 64 Kbit/s and below are sampled at 22kHz. The reverse process - converting
MP3 files to CD audio tracks - also involves two discrete stages. The
decoding of an MP3 file to a WAV file is performed by a specialised program
known as an MP3 Decoder. Getting the WAV file to CD is a function of
the various specialised applications that exist for creating CDRs or
CD-RWs, such as Easy CD Creator or WinonCD.
Notwithstanding Diamond's success in the US courts, there are
issues concerning the use of MP3 technology. Whilst the British
Phonographic Industry (BPI) maintain that it is illegal to make
copies of a CD/tape/record even if it is for your own use, this
is "unenforceable" under UK law and in reality the practice
is widespread. Downloading licensed MP3 files from the Internet
is perfectly legal, but it is illegal to encode MP3s and trade
them with others unless this is done with the express permission
of the copyright holder of the music. There are many legal tracks
in MP3 format available freely on the Internet that have the permission
of their copyright holders - mostly by unknown artists looking
for free publicity. However, it's generally accepted that the vast
majority of MP3 music files are illegal - they are unlicensed recordings
of copyrighted work - and though there are some major artists who
have sought to promote their music over the Internet using MP3,
this has invariably been met with opposition. Interestingly, shortly
after its courtroom success, Diamond appeared to be making moves
to pacify the record labels with the announcement that the new
model will feature anti-piracy software to prevent unauthorised
copying of MP3 files and be upgradeable, via the Internet, to play
whatever standard was ultimately recommended by the Secure Digital
Music Initiative (SDMI).
One company that is unlikely to be making an MP3 player in the
near future is Sony, the inventor of MiniDisc (MD), which has been
the emerging digital audio recording standard of the late 1990s.
The Rio is both lighter and smaller than most MD players, however,
and has the additional advantage of containing no moving parts.
This means that no matter how roughly handled, unlike CD or MD,
the music won't skip a beat. The Rio also exerts less of a power
drain than laser-based products, yielding a claimed 12 hours from
a single alkaline battery.
The first Rio device came to market towards the end of 1998, bundled
with conversion software capable of digitally extracting CD audio
and creating 64-, 80-, or 128 Kbit/s MP3 files. The upper and lower
rates equate to 33 minutes of FM quality and 66 minutes of CD quality
capacity respectively, from the device's 32MB of internal memory.
Storage capacity can be expanded, up to 64MB, via an add-in SmartMedia
flash memory card. Mid-1999 - following the rejection of the RIAA's
lawsuit and the acquisition of Diamond by graphics-chip manufacturer
S3 - saw the Rio business spun-off to a newly formed RioPort division
and the announcement of a new model providing double the on-board
memory of the earlier model, expandable to 96MB. The incorporation
of IBM's 340MB microdrive unit - 1in in size and weighing only
16-grams - into subsequent Rios boosted capacity to up to six hours
of near-CD quality MP3 music.
In 2000 a number of players appeared - both portable and designed
to complement home hi-fi systems - that handled both conventional
CDs and recordable CDs containing MP3-encoded tracks. Whilst these
may not have been "skip-free", this was more than compensated
for by their massive, 10-hour capacity. If there had been any doubt
about MP3's acceptance into the mainstream before, they were removed
by the participation of consumer giants such as Philips Electronics
in this marketplace.
MP3 may have been a phenomenon of the late 1990s, but it will
almost certainly be eclipsed early in the new millennium. Since
its development in 1995 a number of new formats have emerged -
many of which give even better compression and comparable quality.
AAC (Advanced Audio Compression), for example, can produce files
that are 30% to 40% smaller than MP3 files, whilst retaining their
level of quality.
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